                       Kea Administrator Reference Manual

   This is the reference guide for Kea version 1.0.0.

   Copyright (c) 2010-2015 Internet Systems Consortium, Inc.

   Abstract

   Kea is an open source implementation of the Dynamic Host Configuration
   Protocol (DHCP) servers, developed and maintained by Internet Systems
   Consortium (ISC).

   This is the reference guide for Kea version 1.0.0. The most up-to-date
   version of this document (in PDF, HTML, and plain text formats), along
   with other documents for Kea, can be found at http://kea.isc.org/docs.

   --------------------------------------------------------------------------

   Table of Contents

   1. Introduction

                1.1. Supported Platforms

                1.2. Required Software at Run-time

                1.3. Kea Software

   2. Quick start

                2.1. Quick start guide for DHCPv4 and DHCPv6 services

                2.2. Running Kea servers directly

   3. Installation

                3.1. Packages

                3.2. Install Hierarchy

                3.3. Building Requirements

                3.4. Installation from Source

                             3.4.1. Download Tar File

                             3.4.2. Retrieve from Git

                             3.4.3. Configure before the build

                             3.4.4. Build

                             3.4.5. Install

                3.5. Selecting the Configuration Backend

                3.6. DHCP Database Installation and Configuration

                             3.6.1. Building with MySQL Support

                             3.6.2. Building with PostgreSQL support

   4. Kea Database Administration

                4.1. Databases and Database Version Numbers

                4.2. The kea-admin Tool

                4.3. Supported Databases

                             4.3.1. memfile

                             4.3.2. MySQL

                             4.3.3. PostgreSQL

                             4.3.4. Limitations related to the use of the SQL
                             databases

   5. Kea configuration

                5.1. JSON configuration backend

                             5.1.1. JSON syntax

                             5.1.2. Simplified Notation

   6. Managing Kea with keactrl

                6.1. Overview

                6.2. Command Line Options

                6.3. The keactrl Configuration File

                6.4. Commands

                6.5. Overriding the Server Selection

   7. The DHCPv4 Server

                7.1. Starting and Stopping the DHCPv4 Server

                7.2. DHCPv4 Server Configuration

                             7.2.1. Introduction

                             7.2.2. Lease Storage

                             7.2.3. Hosts Storage

                             7.2.4. Interface configuration

                             7.2.5. Issues with unicast responses to
                             DHCPINFORM

                             7.2.6. IPv4 Subnet Identifier

                             7.2.7. Configuration of IPv4 Address Pools

                             7.2.8. Standard DHCPv4 options

                             7.2.9. Custom DHCPv4 options

                             7.2.10. DHCPv4 Vendor Specific Options

                             7.2.11. Nested DHCPv4 Options (Custom Option
                             Spaces)

                             7.2.12. Unspecified parameters for DHCPv4 option
                             configuration

                             7.2.13. Stateless Configuration of DHCPv4
                             clients

                             7.2.14. Client Classification in DHCPv4

                             7.2.15. Configuring DHCPv4 for DDNS

                             7.2.16. Next Server (siaddr)

                             7.2.17. Echoing Client-ID (RFC 6842)

                             7.2.18. Using Client Identifier and Hardware
                             Address

                7.3. Host reservation in DHCPv4

                             7.3.1. Address reservation types

                             7.3.2. Conflicts in DHCPv4 reservations

                             7.3.3. Reserving a hostname

                             7.3.4. Reserving specific options

                             7.3.5. Fine Tuning IPv4 Host Reservation

                7.4. Server Identifier in DHCPv4

                7.5. How the DHCPv4 Server Selects a Subnet for the Client

                             7.5.1. Using a Specific Relay Agent for a Subnet

                             7.5.2. Segregating IPv4 Clients in a Cable
                             Network

                7.6. Duplicate Addresses (DHCPDECLINE support)

                7.7. Statistics in DHCPv4 server

                7.8. Management API for the DHCPv4 server

                7.9. Supported DHCP Standards

                7.10. DHCPv4 Server Limitations

   8. The DHCPv6 Server

                8.1. Starting and Stopping the DHCPv6 Server

                8.2. DHCPv6 Server Configuration

                             8.2.1. Introduction

                             8.2.2. Lease Storage

                             8.2.3. Interface selection

                             8.2.4. IPv6 Subnet Identifier

                             8.2.5. Unicast traffic support

                             8.2.6. Subnet and Address Pool

                             8.2.7. Subnet and Prefix Delegation Pools

                             8.2.8. Standard DHCPv6 options

                             8.2.9. Custom DHCPv6 options

                             8.2.10. DHCPv6 vendor specific options

                             8.2.11. Nested DHCPv6 options (custom option
                             spaces)

                             8.2.12. Unspecified parameters for DHCPv6 option
                             configuration

                             8.2.13. IPv6 Subnet Selection

                             8.2.14. Rapid Commit

                             8.2.15. DHCPv6 Relays

                             8.2.16. Relay-Supplied Options

                             8.2.17. Client Classification in DHCPv6

                             8.2.18. Configuring DHCPv6 for DDNS

                8.3. Host reservation in DHCPv6

                             8.3.1. Address/prefix reservation types

                             8.3.2. Conflicts in DHCPv6 reservations

                             8.3.3. Reserving a hostname

                             8.3.4. Reserving specific options

                             8.3.5. Fine Tuning IPv6 Host Reservation

                8.4. Server Identifier in DHCPv6

                8.5. Stateless DHCPv6 (Information-Request Message)

                8.6. Support for RFC 7550

                8.7. Using specific relay agent for a subnet

                8.8. Segregating IPv6 clients in a cable network

                8.9. MAC/Hardware addresses in DHCPv6

                8.10. Duplicate Addresses (DECLINE support)

                8.11. Statistics in DHCPv6 server

                8.12. Management API for the DHCPv6 server

                8.13. Supported DHCPv6 Standards

                8.14. DHCPv6 Server Limitations

   9. Lease Expiration in DHCPv4 and DHCPv6

                9.1. Lease Reclamation

                9.2. Configuring Leases Reclamation

                9.3. Configuring Lease Affinity

                9.4. Default Configuration Values for Leases Reclamation

                9.5. Reclaiming Expired Leases with Command

   10. The DHCP-DDNS Server

                10.1. Starting and Stopping the DHCP-DDNS Server

                10.2. Configuring the DHCP-DDNS Server

                             10.2.1. Global Server Parameters

                             10.2.2. TSIG Key List

                             10.2.3. Forward DDNS

                             10.2.4. Reverse DDNS

                             10.2.5. Example DHCP-DDNS Server Configuration

                10.3. DHCP-DDNS Server Limitations

   11. The LFC process

                11.1. Overview

                11.2. Command Line Options

   12. Client Classification

                12.1. Client Classification Overview

                12.2. Using Vendor Class Information In Classification

                12.3. Using Expressions In Classification

                             12.3.1. Substring

                12.4. Configuring Classes

                12.5. Configuring Subnets With Class Information

                12.6. Using Classes

                12.7. Classes and Hooks

   13. Hooks Libraries

                13.1. Introduction

                13.2. Configuring Hooks Libraries

   14. Statistics

                14.1. Statistics Overview

                14.2. Statistics Lifecycle

                14.3. Commands for Manipulating Statistics

                             14.3.1. statistic-get command

                             14.3.2. statistic-reset command

                             14.3.3. statistic-remove command

                             14.3.4. statistic-get-all command

                             14.3.5. statistic-reset-all command

                             14.3.6. statistic-remove-all command

   15. Management API

                15.1. Data syntax

                15.2. Using control channel

                15.3. Commands supported by both DHCPv4 and DHCPv6 servers

                             15.3.1. leases-reclaim command

                             15.3.2. list-commands command

                             15.3.3. shutdown command

   16. libdhcp++ library

                16.1. Interface detection and Socket handling

   17. Logging

                17.1. Logging Configuration

                             17.1.1. Loggers

                             17.1.2. Output Options

                             17.1.3. Example Logger Configurations

                17.2. Logging Message Format

                17.3. Logging During Kea Startup

   18. Frequently Asked Questions

                18.1. Generic Frequently Asked Questions

                             18.1.1. Where did the Kea name came from?

                             18.1.2. Feature X is not supported yet. When/if
                             will it be available?

                18.2. Frequently Asked Questions about DHCPv4

                             18.2.1. I set up a firewall, but the Kea server
                             still receives the traffic. Why?

                18.3. Frequently Asked Questions about DHCPv6

                             18.3.1. Kea DHCPv6 doesn't seem to get incoming
                             traffic. I checked with tcpdump (or other
                             traffic capture software) that the incoming
                             traffic is reaching the box. What's wrong?

   19. Acknowledgments

   List of Tables

   7.1. List of standard DHCPv4 options

   7.2. List of standard DHCPv4 options (continued)

   7.3. List of standard DHCP option types

   7.4. Default FQDN Flag Behavior

   7.5. DHCPv4 Statistics

   8.1. List of standard DHCPv6 options

   8.2. List of experimental DHCPv6 options

   8.3. Default FQDN Flag Behavior

   8.4. DHCPv6 Statistics

   10.1. Our example network

   10.2. Forward DDNS Domains Needed

   10.3. Reverse DDNS Domains Needed

   12.1. List of Classification Values

   12.2. List of Classification Expressions

                            Chapter 1. Introduction

   Table of Contents

   1.1. Supported Platforms

   1.2. Required Software at Run-time

   1.3. Kea Software

   Kea is the next generation of DHCP software developed by ISC. It supports
   both DHCPv4 and DHCPv6 protocols along with their extensions, e.g. prefix
   delegation and dynamic updates to DNS.

   Kea was initially developed as a part of the BIND 10 framework. In early
   2014, ISC made the decision to discontinue active development of BIND 10
   and continue development of Kea as standalone DHCP software.

   This guide covers Kea version 1.0.0.

1.1. Supported Platforms

   Kea is officially supported on Red Hat Enterprise Linux, CentOS, Fedora
   and FreeBSD systems. It is also likely to work on many other platforms:
   builds have been tested on (in no particular order) Debian GNU/Linux 6 and
   unstable, Ubuntu 9.10, NetBSD 5, Solaris 10 and 11, FreeBSD 7 and 8,
   CentOS Linux 5.3, MacOS 10.6 and 10.7, and OpenBSD 5.1. Non supported
   systems (especially non-Linux) are likely to have issues with directly
   connected DHCPv4 clients.

   There are currently no plans to port Kea to Windows platforms.

1.2. Required Software at Run-time

   Running Kea uses various extra software which may not be provided in the
   default installation of some operating systems, nor in the standard
   package collections. You may need to install this required software
   separately. (For the build requirements, also see Section 3.3, "Building
   Requirements".)

     * Kea supports two crypto libraries: Botan and OpenSSL. Only one of them
       is required to be installed during compilation. Kea uses the Botan
       crypto library for C++ (http://botan.randombit.net/), version 1.8 or
       later. As an alternative to Botan, Kea can use the OpenSSL crypto
       library (http://www.openssl.org/). It requires a version with SHA-2
       support.
     * Kea uses the log4cplus C++ logging library
       (http://log4cplus.sourceforge.net/). It requires at least log4cplus
       version 1.0.3.
     * In order to store lease information in a MySQL database, Kea requires
       MySQL headers and libraries. This is an optional dependency in that
       Kea can be built without MySQL support.
     * In order to store lease information in a PostgreSQL database, Kea
       requires PostgreSQL headers and libraries. This is an optional
       dependency in that Kea can be built without PostgreSQL support.

1.3. Kea Software

   Kea is modular. Part of this modularity is accomplished using multiple
   cooperating processes which, together, provide the server functionality.
   The following software is included with Kea:

     * keactrl -- Tool to start, stop, reconfigure, and report status for the
       Kea servers.
     * kea-dhcp4 -- DHCPv4 server process. This process responds to DHCPv4
       queries from clients.
     * kea-dhcp6 -- DHCPv6 server process. This process responds to DHCPv6
       queries from clients.
     * kea-dhcp-ddns -- DHCP-DDNS process. This process acts as an
       intermediary between the DHCP servers and DNS server. It receives name
       update requests from the DHCP servers and sends DNS Update messages to
       the DNS servers.
     * kea-admin -- A tool useful for database backend maintenance (creating
       new database, checking versions, upgrading etc.)
     * kea-lfc -- This process removes redundant information from the files
       used to provide persistent storage for the memfile data base backend.
       The service is written to run as a stand alone process. While it can
       be started externally it should be started by the Kea DHCP servers.
     * perfdhcp -- DHCP benchmarking tool which simulates multiple clients to
       test both DHCPv4 and DHCPv6 servers performance.

   The tools and modules are covered in full detail in this guide. In
   addition, manual pages are also provided in the default installation.

   Kea also provides C++ libraries and programmer interfaces for DHCP. These
   include detailed developer documentation and code examples.

                             Chapter 2. Quick start

   Table of Contents

   2.1. Quick start guide for DHCPv4 and DHCPv6 services

   2.2. Running Kea servers directly

   This quickly covers the standard steps for installing and deploying Kea.
   For further details, full customizations, and troubleshooting, see the
   respective chapters in the Kea guide.

2.1. Quick start guide for DHCPv4 and DHCPv6 services

    1. Install required run-time and build dependencies. See Section 3.3,
       "Building Requirements" for details.
    2. Download Kea source tarball from ISC.org downloads page or ISC ftp
       server.

    3. Extract the tarball. For example:

 $ tar xvzf kea-1.0.0.tar.gz

    4. Go into the source directory and run the configure script:

 $ cd kea-1.0.0
 $ ./configure [your extra parameters]

    5. Build it:

 $ make

    6. Install it (by default the installation prefix is /usr/local/, so you
       likely need root privileges for that step):

 # make install

    7. Edit the configuration file which by default is installed in
       [kea-install-dir]/etc/kea/kea.conf and contains configuration for all
       Kea services. Configuration choices for DHCPv4 and DHCPv6 services are
       described in Section 7.2, "DHCPv4 Server Configuration" and
       Section 8.2, "DHCPv6 Server Configuration", respectively.

    8. In order to start the DHCPv4 server in background, run the following
       command (as root):

 # keactrl start -s dhcp4

       Or run the following command to start DHCPv6 server instead:

 # keactrl start -s dhcp6

       Note that it is also possible to start both servers simultaneously:

 $ keactrl start

    9. Verify that Kea server(s) are running:

 # keactrl status

       If the server status is "inactive" may indicate a configuration error.
       Please check a log file (by default located in
       [kea-install-dir]/var/kea/kea.log) for the details of the error.

   10. If the server has been started successfully, test that it is
       responding to DHCP queries and that the client receives a
       configuration from the server; for example, use the ISC DHCP client.

   11. Stop running server(s):

 # keactrl stop

   For more system specific installation procedures, you may want to visit
   System specific notes, available on Kea homepage.

   The details of keactrl script usage can be found in Chapter 6, Managing
   Kea with keactrl.

2.2. Running Kea servers directly

   Kea servers can be started directly (without a need to use keactrl). To
   start DHCPv4 server run the following command:

 # kea-dhcp4 -c /path/to/your/kea4/config/file.json

   And, to start the DHCPv6 server run the following command:

 # kea-dhcp6 -c /path/to/your/kea6/config/file.json

                            Chapter 3. Installation

   Table of Contents

   3.1. Packages

   3.2. Install Hierarchy

   3.3. Building Requirements

   3.4. Installation from Source

                3.4.1. Download Tar File

                3.4.2. Retrieve from Git

                3.4.3. Configure before the build

                3.4.4. Build

                3.4.5. Install

   3.5. Selecting the Configuration Backend

   3.6. DHCP Database Installation and Configuration

                3.6.1. Building with MySQL Support

                3.6.2. Building with PostgreSQL support

3.1. Packages

   Some operating systems or software package vendors may provide
   ready-to-use, pre-built software packages for Kea. Installing a pre-built
   package means you do not need to install build-only prerequisites and do
   not need to make the software.

   FreeBSD ports, NetBSD pkgsrc, and Debian testing package collections
   provide all the prerequisite packages.

3.2. Install Hierarchy

   The following is the directory layout of the complete Kea installation
   (all directories paths are relative to the installation directory):

     * etc/kea/ -- configuration files.
     * include/ -- C++ development header files.
     * lib/ -- libraries.
     * sbin/ -- server software and commands used by the system
       administrator.
     * share/kea/ -- configuration specifications and examples.
     * share/doc/kea/ -- this guide, other supplementary documentation, and
       examples.
     * share/man/ -- manual pages (online documentation).
     * var/kea/ -- server identification, lease databases, and log files.

3.3. Building Requirements

   In addition to the run-time requirements (listed in Section 1.2, "Required
   Software at Run-time"), building Kea from source code requires various
   development include headers and program development tools.

  Note

   Some operating systems have split their distribution packages into a
   run-time and a development package. You will need to install the
   development package versions, which include header files and libraries, to
   build Kea from the source code.

   Building from source code requires the following software installed on the
   system:

     * Boost build-time headers (http://www.boost.org/). At least Boost
       version 1.35 is required. When header-only Boost error code is not
       available or wanted, the Boost system library is required too.

     * Botan (at least version 1.8) or OpenSSL.

     * log4cplus (at least version 1.0.3) development include headers.

     * A C++ compiler and standard development headers. Kea builds have been
       tested with GCC g++ 3.4.3, 4.1.2, 4.1.3, 4.2.1, 4.3.2, and 4.4.1;
       Clang++ 2.8; and Sun C++ 5.10.

     * The development tools "make".

   Visit the user-contributed wiki at
   http://kea.isc.org/wiki/SystemSpecificNotes for system-specific
   installation tips.

3.4. Installation from Source

   Kea is open source software written in C++. It is freely available in
   source code form from ISC as a downloadable tar file or via Kea Git code
   revision control service. (It may also be available in pre-compiled
   ready-to-use packages from operating system vendors.)

  3.4.1. Download Tar File

   The Kea release tarballs may be downloaded from:
   http://ftp.isc.org/isc/kea/ (using FTP or HTTP).

  3.4.2. Retrieve from Git

   Downloading this "bleeding edge" code is recommended only for developers
   or advanced users. Using development code in a production environment is
   not recommended.

  Note

   When building from source code retrieved via Git, additional software will
   be required: automake (v1.11 or later), libtoolize, and autoconf (2.59 or
   later). These may need to be installed.

   The latest development code (together with temporary experiments and
   un-reviewed code) is available via the Kea code revision control system.
   This is powered by Git and all the Kea development is public. The leading
   development is done in the "master" branch.

   The code can be checked out from git://git.kea.isc.org/kea:

 $ git clone git://git.kea.isc.org/kea

   The code checked out from the git repository doesn't include the generated
   configure script, Makefile.in files, nor their related build files. They
   can be created by running autoreconf with the --install switch. This will
   run autoconf, aclocal, libtoolize, autoheader, automake, and related
   commands.

  3.4.3. Configure before the build

   Kea uses the GNU Build System to discover build environment details. To
   generate the makefiles using the defaults, simply run:

 $ ./configure

   Run ./configure with the --help switch to view the different options. Some
   commonly-used options are:

   --prefix
           Define the installation location (the default is /usr/local).

   --with-boost-include
           Define the path to find the Boost headers.

   --with-boost-libs
           Specify Boost libraries to link with (this option exists only to
           provide a way to enforce such a list: usually this should not be
           used).

   --with-boost-lib-dir
           Specify the path to Boost libraries to link with (usually there
           should be no reason to specify this option).

   --with-botan-config
           Specify the path to the botan-config script to build with Botan
           for the crypto code.

   --with-gtest
           Enable the building of the C++ Unit Tests using the Google Test
           framework. Optionally this can define the path to the gtest header
           files and library. (If the framework is not already installed on
           your system, it can be downloaded from
           https://code.google.com/p/googletest.)

   --with-log4cplus
           Define the path to find the Log4cplus headers and libraries.

   --with-openssl
           Replace Botan by OpenSSL for the crypto library. The default is to
           try to find a working Botan then OpenSSL only if Botan is not
           found.

   --without-werror
           Disable the default use of the -Werror compiler flag so that
           compiler warnings do not result in build failures.

  Note

   For additional instructions concerning the building and installation of
   Kea for various databases, see Section 3.6, "DHCP Database Installation
   and Configuration". For additional instructions concerning the
   configuration backends, see Section 3.5, "Selecting the Configuration
   Backend".

   For example, the following command configures Kea to find the Boost
   headers in /usr/pkg/include, specifies that PostgreSQL support should be
   enabled, and sets the installation location to /opt/kea:

 $ ./configure \
       --with-boost-include=/usr/pkg/include \
       --with-dhcp-pgsql=/usr/local/bin/pg_config \
       --prefix=/opt/kea

   If you have some problems with building Kea using the header-only Boost
   error code or you'd like to use the Boost system library (e.g., located in
   /usr/pkg/lib):

 $ ./configure \
       --with-boost-libs=-lboost_system \
       --with-boost-lib-dir=/usr/pkg/lib

   If the configure fails, it may be due to missing or old dependencies.

   ./configure when it succeeds displays a report with the building
   parameters. This report is saved into config.report and embedded into
   executable binaries, e.g., kea-dhcp4.

  3.4.4. Build

   After the configure step is complete, build the executables from the C++
   code and prepare the Python scripts by running the command:

 $ make

  3.4.5. Install

   To install the Kea executables, support files, and documentation, issue
   the command:

 $ make install

   Do not use any form of parallel or job server options (such as GNU make's
   -j option) when performing this step: doing so may cause errors.

  Note

   The install step may require superuser privileges.

   If required, run ldconfig as root with /usr/local/lib (or with
   ${prefix}/lib if configured with --prefix) in /etc/ld.so.conf (or the
   relevant linker cache configuration file for your OS):

 $ ldconfig

  Note

   If you do not run ldconfig where it is required, you may see errors like
   the following:

               program: error while loading shared libraries: libkea-something.so.1:
               cannot open shared object file: No such file or directory


3.5. Selecting the Configuration Backend

   Kea 0.9 has introduced configuration backends that are switchable during
   the compilation phase. Only one backend, JSON, is currently supported.

   JSON
           JSON is the new default configuration backend that causes Kea to
           read JSON configuration files from disk. It does not require any
           framework and thus is considered more lightweight. It will allow
           dynamic on-line reconfiguration, but will lack remote capabilities
           (i.e. no RESTful API).

3.6. DHCP Database Installation and Configuration

   Kea stores its leases in a lease database. The software has been written
   in a way that makes it possible to choose which database product should be
   used to store the lease information. At present, Kea supports three
   database backends: MySQL, PostgreSQL and Memfile. To limit external
   dependencies, both MySQL and PostgreSQL support are disabled by default
   and only Memfile is available. Support for the optional external database
   backend must be explicitly included when Kea is built. This section covers
   the building of Kea with MySQL and/or PostgreSQL and the creation of the
   lease database.

  3.6.1. Building with MySQL Support

   Install MySQL according to the instructions for your system. The client
   development libraries must be installed.

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the MySQL database code, at the
   "configure" step (see Section 3.4.3, "Configure before the build"), do:

 ./configure [other-options] --with-dhcp-mysql

   Or specify the location of the MySQL configuration program "mysql_config"
   if MySQL was not installed in the default location:

 ./configure [other-options] --with-dhcp-mysql=path-to-mysql_config

   See Section 4.3.2.1, "First Time Creation of Kea Database" for details
   regarding MySQL database configuration.

  3.6.2. Building with PostgreSQL support

   Install PostgreSQL according to the instructions for your system. The
   client development libraries must be installed. Client development
   libraries are often packaged as "libpq".

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the PostgreSQL database code, at the
   "configure" step (see Section 3.4.3, "Configure before the build"), do:

 ./configure [other-options] --with-dhcp-pgsql

   Or specify the location of the PostgreSQL configuration program
   "pg_config" if PostgreSQL was not installed in the default location:

 ./configure [other-options] --with-dhcp-pgsql=path-to-pg_config

   See Section 4.3.3.1, "Manually Create the PostgreSQL Database and the Kea
   User" for details regarding PostgreSQL database configuration.

                     Chapter 4. Kea Database Administration

   Table of Contents

   4.1. Databases and Database Version Numbers

   4.2. The kea-admin Tool

   4.3. Supported Databases

                4.3.1. memfile

                4.3.2. MySQL

                4.3.3. PostgreSQL

                4.3.4. Limitations related to the use of the SQL databases

4.1. Databases and Database Version Numbers

   Kea stores leases in one of several supported databases. As future
   versions of Kea are released, the structure of those databases will
   change. For example, Kea currently only stores lease information: in the
   future, additional data - such as host reservation details - will also be
   stored.

   A given version of Kea expects a particular structure in the database. It
   ensures this by checking the version of the database it is using. Separate
   version numbers are maintained for backend databases, independent of the
   version of Kea itself. It is possible that the backend database version
   will stay the same through several Kea revisions. Likewise, it is possible
   that the version of backend database may go up several revisions during a
   Kea upgrade. Versions for each database are independent, so an increment
   in the MySQL database version does not imply an increment in that of
   PostgreSQL.

   Backend versions are specified in a major.minor format. The minor number
   is increased when there are backward compatible changes introduced. For
   example, the addition of a new index. It is desirable, but not mandatory
   to apply such a change; you can run on older database version if you want
   to. (Although, in the example given, running without the new index may be
   at the expense of a performance penalty.) On the other hand, the major
   number is increased when an incompatible change is introduced, for example
   an extra column is added to a table. If you try to run Kea software on a
   database that is too old (as signified by mismatched backend major version
   number), Kea will refuse to run: administrative action will be required to
   upgrade the database.

4.2. The kea-admin Tool

   To manage the databases, Kea provides the kea-admin tool. It is able to
   initialize a new database, check its version number, perform a database
   upgrade, and dump lease data to a text file.

   kea-admin takes two mandatory parameters: command and backend. Additional,
   non-mandatory options may be specified. Currently supported commands are:

     * lease-init -- Initializes a new lease database. Useful during first
       Kea installation. The database is initialized to the latest version
       supported by the version of the software.
     * lease-version -- Reports the lease database version number. This is
       not necessarily equal to the Kea version number as each backend has
       its own versioning scheme.
     * lease-upgrade -- Conducts a lease database upgrade. This is useful
       when upgrading Kea.
     * lease-dump -- Dumps the contents of the lease database (for MySQL or
       PostgreSQL backends) to CSV text file. The first line of the file
       contains the column names. This is meant to be used as a diagnostic
       tool that provides a portable, human-readable form of lease data.

   backend specifies the backend type. Currently supported types are:

     * memfile -- Lease information is stored on disk in a text file.
     * mysql -- Lease information is stored in a MySQL relational database.
     * pgsql -- Lease information is stored in a PostgreSQL relational
       database.

   Additional parameters may be needed, depending on your setup and specific
   operation: username, password and database name or the directory where
   specific files are located. See appropriate manual page for details (man 8
   kea-admin).

4.3. Supported Databases

  4.3.1. memfile

   There are no special initialization steps necessary for the memfile
   backend. During the first run, both kea-dhcp4 and kea-dhcp6 will create an
   empty lease file if one is not present. Necessary disk write permission is
   required.

    4.3.1.1. Upgrading Memfile Lease Files from an Earlier Version of Kea

   There are no special steps required to upgrade memfile lease files from an
   earlier version of Kea to a new version of Kea. During startup the servers
   will check the schema version of the lease files against their own. If
   there is a mismatch, the servers will automatically launch the LFC process
   to convert the files to the server's schema version. While this mechanism
   is primarily meant to ease the process of upgrading to newer versions of
   Kea, it can also be used for downgrading should the need arise. When
   upgrading, any values not present in the original lease files will be
   assigned appropriate default values. When downgrading, any data present in
   the files but not in the server's schema will be dropped. If you wish to
   convert the files manually, prior to starting the servers you may do so by
   running the LFC process yourself. See Chapter 11, The LFC process for more
   information.

  4.3.2. MySQL

   The MySQL database must be properly set up if you want Kea to store
   information in MySQL. This section can be safely ignored if you chose to
   store the data in other backends.

    4.3.2.1. First Time Creation of Kea Database

   If you are setting the MySQL database for the first time, you need to
   create the database area within MySQL and set up the MySQL user ID under
   which Kea will access the database. This needs to be done manually:
   kea-admin is not able to do this for you.

   To create the database:

    1. Log into MySQL as "root":

 $ mysql -u root -p
 Enter password:
 mysql>

    2. Create the MySQL database:

 mysql> CREATE DATABASE database-name;

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database tables:

 mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
 mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';

       (user-name and password are the user ID and password you are using to
       allow Keas access to the MySQL instance. All apostrophes in the
       command lines above are required.)

    4. At this point, you may elect to create the database tables.
       (Alternatively, you can exit MySQL and create the tables using the
       kea-admin tool, as explained below.) To do this:

 mysql> CONNECT database-name;
 mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql

       (path-to-kea is the location where you installed Kea.)

    5. Exit MySQL:

 mysql> quit
 Bye
 $

   If you elected not to create the tables in step 4, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init mysql -u database-user -p database-password -n database-name

   (Do not do this if you did create the tables in step 4.) kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin.)

    4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea

   Sometimes a new Kea version may use newer database schema, so there will
   be a need to upgrade the existing database. This can be done using the
   kea-admin lease-upgrade command.

   To check the current version of the database, use the following command:

 $ kea-admin lease-version mysql -u database-user -p database-password -n database-name

   (See Section 4.1, "Databases and Database Version Numbers" for a
   discussion about versioning.) If the version does not match the minimum
   required for the new version of Kea (as described in the release notes),
   the database needs to be upgraded.

   Before upgrading, please make sure that the database is backed up. The
   upgrade process does not discard any data but, depending on the nature of
   the changes, it may be impossible to subsequently downgrade to an earlier
   version. To perform an upgrade, issue the following command:

 $ kea-admin lease-upgrade mysql -u database-user -p database-password -n database-name

  4.3.3. PostgreSQL

   A PostgreSQL database must be set up if you want Kea to store lease and
   other information in PostgreSQL. This step can be safely ignored if you
   are using other database backends.

    4.3.3.1. Manually Create the PostgreSQL Database and the Kea User

   The first task is to create both the lease database and the user under
   which the servers will access it. A number of steps are required:

    1. Log into PostgreSQL as "root":

 $ sudo -u postgres psql postgres
 Enter password:
 postgres=#

    2. Create the database:

 postgres=# CREATE DATABASE database-name;
 CREATE DATABASE
 postgres=#

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database:

 postgres=# CREATE USER user-name WITH PASSWORD 'password';
 CREATE ROLE
 postgres=#
 postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
 GRANT
 postgres=#

    4. Exit PostgreSQL:

 postgres=# \q
 Bye
 $

    5. At this point you are ready to create the database tables. This can be
       done using the kea-admin tool as explained in the next section
       (recommended), or manually. To create the tables manually enter the
       following command. Note that PostgreSQL will prompt you to enter the
       new user's password you specified in Step 3. When the command
       completes you will be returned to the shell prompt. You should see
       output similar to following:

 $ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
 Password for user user-name:
 CREATE TABLE
 CREATE INDEX
 CREATE INDEX
 CREATE TABLE
 CREATE INDEX
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 INSERT 0 1
 INSERT 0 1
 COMMIT
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 COMMIT
 $

       (path-to-kea is the location where you installed Kea.)

       If instead you encounter an error like:

 psql: FATAL:  no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off

       ... you will need to alter the PostgreSQL configuration. Kea uses
       password authentication when connecting to the database and must have
       the appropriate entries added to PostgreSQL's pg_hba.conf file. This
       file is normally located in the primary data directory for your
       PostgreSQL server. The precise path may vary but the default location
       for PostgreSQL 9.3 on Centos 6.5 is:
       /var/lib/pgsql/9.3/data/pg_hba.conf.

       Assuming Kea is running on the same host as PostgreSQL, adding lines
       similar to following should be sufficient to provide
       password-authenticated access to Kea's database:

 local   database-name    user-name                                 password
 host    database-name    user-name          127.0.0.1/32           password
 host    database-name    user-name          ::1/128                password

       These edits are primarily intended as a starting point not a
       definitive reference on PostgreSQL administration or database
       security. Please consult your PostgreSQL user manual before making
       these changes as they may expose other databases that you run. It may
       be necessary to restart PostgreSQL in order for these changes to take
       effect.

    4.3.3.2. Initialize the PostgreSQL Database Using kea-admin

   If you elected not to create the tables manually, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init pgsql -u database-user -p database-password -n database-name

   Do not do this if you already created the tables in manually. kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin.)

    4.3.3.3. Upgrading a PostgreSQL Database from an Earlier Version of Kea

   Currently, PostgreSQL only supports Kea schema version 1.0 so no upgrades
   are available. As upgrades become available, kea-admin will support them.

  4.3.4. Limitations related to the use of the SQL databases

   The lease expiration time is stored in the SQL database for each lease as
   a timestamp value. Kea developers observed that MySQL database doesn't
   accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
   from the beginning of the epoch. At the same time, some versions of
   PostgreSQL do accept greater values but the value is altered when it is
   read back. For this reason the lease database backends put the restriction
   for the maximum timestamp to be stored in the database, which is equal to
   the maximum signed 32-bit number. This effectively means that the current
   Kea version can't store the leases which expiration time is later than
   2147483647 seconds since the beginning of the epoch (around year 2038).

                          Chapter 5. Kea configuration

   Table of Contents

   5.1. JSON configuration backend

                5.1.1. JSON syntax

                5.1.2. Simplified Notation

   Kea is designed to allow different methods by which it can be configured,
   each method being implemented by a component known as a configuration
   backend. At present, only one such backend is available, that allowing
   configuration by means of a JSON file.

5.1. JSON configuration backend

   JSON is the default configuration backend. It assumes that the servers are
   started from the command line (either directly or using a script, e.g.
   keactrl). The JSON backend uses certain signals to influence Kea. The
   configuration file is specified upon startup using the -c parameter.

  5.1.1. JSON syntax

   Configuration files for DHCPv4, DHCPv6 and DDNS modules are defined in an
   extended JSON format. Basic JSON is defined in RFC 4627. Kea components
   use a slightly modified JSON, in that they allow shell-style comments in
   the file: lines with the hash (#) character in the first column are
   comment lines and are ignored.

   The configuration file consists of a single object (often colloquially
   called a map) started with a curly bracket. It comprises the "Dhcp4",
   "Dhcp6", "DhcpDdns" and/or "Logging" objects. It is possible to define
   additional elements, but they will be ignored. For example, it is possible
   to define Dhcp4, Dhcp6 and Logging elements in a single configuration file
   that can be used to start both the DHCPv4 and DHCPv6 components. When
   starting, the DHCPv4 component will use Dhcp4 object to configure itself
   and the Logging object to configure logging parameters; it will ignore the
   Dhcp6 object.

   For example, a very simple configuration for both DHCPv4 and DHCPv6 could
   look like this:

 # The whole configuration starts here.
 {

 # DHCPv4 specific configuration starts here.
 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth0" ],
         "dhcp-socket-type": "raw"
     },
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "subnet4": [{
        "pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
        "subnet": "192.0.2.0/24"
     }],
     ...
 },
 # DHCPv4 specific configuration ends here.

 # DHCPv6 specific configuration starts here.
 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1" ]
     },
     "preferred-lifetime": 3000,
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "subnet6": [{
        "pools": [ { "pool": "2001:db8::/80" } ],
        "subnet": "2001:db8::/64"
     }],
     ...
 },
 # DHCPv6 specific configuration ends here.

 # Logger parameters (that could be shared among several components) start here.
 # This section is used by both the DHCPv4 and DHCPv6 servers.
 "Logging": {
    "loggers": [{
         "name": "*",
         "severity": "DEBUG"
     }],
     ...
 }
 # Logger parameters end here.

 # The whole configuration structure ends here.
 }

   More examples are available in the installed share/doc/kea/examples
   directory.

   To avoid repetition of mostly similar structures, examples in the rest of
   this guide will showcase only the subset of parameters appropriate for a
   given context. For example, when discussing the IPv6 subnets configuration
   in DHCPv6, only subnet6 parameters will be mentioned. It is implied that
   the remaining elements (the global map that holds Dhcp6, Logging and
   possibly DhcpDdns) are present, but they are omitted for clarity. Usually,
   locations where extra parameters may appear are denoted with an ellipsis.

  5.1.2. Simplified Notation

   It is sometimes convenient to refer to a specific element in the
   configuration hierarchy. Each hierarchy level is separated by a slash. If
   there is an array, a specific instance within that array is referenced by
   a number in square brackets (with numbering starting at zero). For
   example, in the above configuration the valid-lifetime in the Dhcp6
   component can be referred to as Dhcp6/valid-lifetime and the pool in the
   first subnet defined in the DHCPv6 configuration as Dhcp6/subnet6[0]/pool.

                      Chapter 6. Managing Kea with keactrl

   Table of Contents

   6.1. Overview

   6.2. Command Line Options

   6.3. The keactrl Configuration File

   6.4. Commands

   6.5. Overriding the Server Selection

6.1. Overview

   keactrl is a shell script which controls the startup, shutdown and
   reconfiguration of the Kea servers (kea-dhcp4, kea-dhcp6 and
   kea-dhcp-ddns). It also provides the means for checking the current status
   of the servers and determining the configuration files in use.

6.2. Command Line Options

   keactrl is run as follows:

 keactrl <command> [-c keactrl-config-file] [-s server[,server,..]]

   <command> is the one of the commands described in Section 6.4, "Commands".

   The optional -c keactrl-config-file switch allows specification of an
   alternate keactrl configuration file. (--ctrl-config is a synonym for -c.)
   In the absence of -c, keactrl will use the default configuration file
   [kea-install-dir]/etc/kea/keactrl.conf.

   The optional -s server[,server ...] switch selects the servers to which
   the command is issued. (--server is a synonym for -s.) If absent, the
   command is sent to all servers enabled in the keactrl configuration file.
   If multiple servers are specified, they should be separated by commas with
   no intervening spaces.

6.3. The keactrl Configuration File

   Depending on requirements, not all of the available servers need be run.
   The keactrl configuration file sets which servers are enabled and which
   are disabled. The default configuration file is
   [kea-install-dir]/etc/kea/keactrl.conf, but this can be overridden on a
   per-command basis using the -c switch.

   The contents of keactrl.conf are:

 # This is a configuration file for keactrl script which controls
 # the startup, shutdown, reconfiguration and gathering the status
 # of the Kea servers.

 # prefix holds the location where the Kea is installed.
 prefix=/usr/local

 # Location of Kea configuration file.
 kea_config_file=${prefix}/etc/kea/kea.conf

 # Location of Kea binaries.
 exec_prefix=${prefix}
 dhcp4_srv=${exec_prefix}/sbin/kea/kea-dhcp4
 dhcp6_srv=${exec_prefix}/sbin/kea/kea-dhcp6
 dhcp_ddns_srv=${exec_prefix}/sbin/kea/kea-dhcp-ddns

 # Start DHCPv4 server?
 dhcp4=yes

 # Start DHCPv6 server?
 dhcp6=yes

 # Start DHCP DDNS server?
 dhcp_ddns=yes

 # Be verbose?
 kea_verbose=no

   The dhcp4, dhcp6 and dhcp_ddns parameters set to "yes" configure keactrl
   to manage (start, reconfigure) all servers, i.e. kea-dhcp4, kea-dhcp6 and
   kea-dhcp-ddns. When any of these parameters is set to "no" the keactrl
   will ignore the corresponding server when starting or reconfiguring Kea.

   By default, Kea servers managed by keactrl are located in
   [kea-install-dir]/sbin. This should work for most installations. If the
   default location needs to be altered for any reason, the paths specified
   with the dhcp4_srv, dhcp6_srv and dhcp_ddns_srv parameters should be
   modified.

   The kea_verbose parameter specifies the verbosity of the servers being
   started. When kea_verbose is set to "yes" the logging level of the server
   is set to DEBUG. Otherwise, the default logging level is used.

  Note

   The verbosity for the server is set when it is started. Once started, the
   verbosity can be only changed by stopping the server and starting it again
   with the new value of the kea_verbose parameter.

6.4. Commands

   The following commands are supported by keactrl to perform specific
   operations on the Kea servers:

     * start - starts selected servers.
     * stop - stops all running servers.
     * reload - triggers reconfiguration of the selected servers by sending
       the SIGHUP signal to them.
     * status - returns the status of the servers (active or inactive) and
       the names of the configuration files in use.

   Typical output from keactrl when starting the servers looks similar to the
   following:

 $ keactrl start
 INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea.conf -d
 INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea.conf -d
 INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea.conf -d

   Kea's servers create PID files upon startup. These files are used by
   keactrl to determine whether or not a given server is running. If one or
   more servers are running when the start command is issued, the output will
   look similar to the following:

 $ keactrl start
 INFO/keactrl: kea-dhcp4 appears to be running, see: PID 10918, PID file: /usr/local/var/kea/kea.kea-dhcp4.pid.
 INFO/keactrl: kea-dhcp6 appears to be running, see: PID 10924, PID file: /usr/local/var/kea/kea.kea-dhcp6.pid.
 INFO/keactrl: kea-dhcp-ddns appears to be running, see: PID 10930, PID file: /usr/local/var/kea/kea.kea-dhcp-ddns.pid.

   During normal shutdowns these PID files are deleted. They may, however, be
   left over as remnants following a system crash. It is possible, though
   highly unlikely, that upon system restart the PIDs they contain actually
   refer to processes unrelated to Kea. This condition will cause keactrl to
   decide that the servers are running, when in fact they are not. In such a
   case the PID files as listed in the keactrl output must be manually
   deleted.

   The following command stops all servers:

 $ keactrl stop
 INFO/keactrl: Stopping kea-dhcp4...
 INFO/keactrl: Stopping kea-dhcp6...
 INFO/keactrl: Stopping kea-dhcp-ddns...

   Note that the stop will attempt to stop all servers regardless of whether
   they are "enabled" in the keactrl.conf. If any of the servers are not
   running, an informational message is displayed as in the stop command
   output below.

 $ keactrl stop
 INFO/keactrl: kea-dhcp4 isn't running.
 INFO/keactrl: kea-dhcp6 isn't running.
 INFO/keactrl: kea-dhcp-ddns isn't running.

   As already mentioned, the reconfiguration of each Kea server is triggered
   by the SIGHUP signal. The reload command sends the SIGHUP signal to the
   servers that are enabled in the keactrl configuration file and are
   currently running. When a server receives the SIGHUP signal it re-reads
   its configuration file and, if the new configuration is valid, uses the
   new configuration. A reload is executed as follows:

 $ keactrl reload
 INFO/keactrl: Reloading kea-dhcp4...
 INFO/keactrl: Reloading kea-dhcp6...
 INFO/keactrl: Reloading kea-dhcp-ddns...

   If any of the servers are not running, an informational message is
   displayed as in the reload command output below.

 $ keactrl stop
 INFO/keactrl: kea-dhcp4 isn't running.
 INFO/keactrl: kea-dhcp6 isn't running.
 INFO/keactrl: kea-dhcp-ddns isn't running.

  Note

   Currently keactrl does not report configuration failures when the server
   is started or reconfigured. To check if the server's configuration
   succeeded the Kea log must be examined for errors. By default, this is
   written to the syslog file.

   Sometimes it is useful to check which servers are running. The status
   reports this, typical output looking like:

 $ keactrl status
 DHCPv4 server: active
 DHCPv6 server: inactive
 DHCP DDNS: active
 Kea configuration file: /usr/local/etc/kea/kea.conf
 keactrl configuration file: /usr/local/etc/kea/keactrl.conf

6.5. Overriding the Server Selection

   The optional -s switch allows the selection of the servers to which
   keactrl command is issued. For example, the following instructs keactrl to
   stop the kea-dhcp4 and kea-dhcp6 servers and leave the kea-dhcp-ddns
   server running:

 $ keactrl stop -s dhcp4,dhcp6

   Similarly, the following will only start the kea-dhcp4 and kea-dhcp-ddns
   servers and not kea-dhcp6.

 $ keactrl start -s dhcp4,dhcp_ddns

   Note that the behavior of the -s switch with the start and reload commands
   is different to its behavior with the stop command. On start and reload,
   keactrl will check if the servers given as parameters to the -s switch are
   enabled in the keactrl configuration file: if not, the server will be
   ignored. For stop however, this check is not made: the command is applied
   to all listed servers, regardless of whether they have been enabled in the
   file.

   The following keywords can be used with the -s command line option:

     * dhcp4 for kea-dhcp4.
     * dhcp6 for kea-dhcp6.
     * dhcp_ddns for kea-dhcp-ddns.
     * all for all servers (default).

                          Chapter 7. The DHCPv4 Server

   Table of Contents

   7.1. Starting and Stopping the DHCPv4 Server

   7.2. DHCPv4 Server Configuration

                7.2.1. Introduction

                7.2.2. Lease Storage

                7.2.3. Hosts Storage

                7.2.4. Interface configuration

                7.2.5. Issues with unicast responses to DHCPINFORM

                7.2.6. IPv4 Subnet Identifier

                7.2.7. Configuration of IPv4 Address Pools

                7.2.8. Standard DHCPv4 options

                7.2.9. Custom DHCPv4 options

                7.2.10. DHCPv4 Vendor Specific Options

                7.2.11. Nested DHCPv4 Options (Custom Option Spaces)

                7.2.12. Unspecified parameters for DHCPv4 option
                configuration

                7.2.13. Stateless Configuration of DHCPv4 clients

                7.2.14. Client Classification in DHCPv4

                7.2.15. Configuring DHCPv4 for DDNS

                7.2.16. Next Server (siaddr)

                7.2.17. Echoing Client-ID (RFC 6842)

                7.2.18. Using Client Identifier and Hardware Address

   7.3. Host reservation in DHCPv4

                7.3.1. Address reservation types

                7.3.2. Conflicts in DHCPv4 reservations

                7.3.3. Reserving a hostname

                7.3.4. Reserving specific options

                7.3.5. Fine Tuning IPv4 Host Reservation

   7.4. Server Identifier in DHCPv4

   7.5. How the DHCPv4 Server Selects a Subnet for the Client

                7.5.1. Using a Specific Relay Agent for a Subnet

                7.5.2. Segregating IPv4 Clients in a Cable Network

   7.6. Duplicate Addresses (DHCPDECLINE support)

   7.7. Statistics in DHCPv4 server

   7.8. Management API for the DHCPv4 server

   7.9. Supported DHCP Standards

   7.10. DHCPv4 Server Limitations

7.1. Starting and Stopping the DHCPv4 Server

   It is recommended that the Kea DHCPv4 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     * -p port - specifies UDP port the server will listen on. This is only
       useful during testing, as the DHCPv4 server listening on ports other
       than default DHCPv4 ports will not be able to handle regular DHCPv4
       queries.
     * -v - prints out Kea version and exits.
     * -V - prints out Kea extended version with additional parameters and
       exits.
     * -W - prints out Kea configuration report and exits.

   The -V command returns the versions of the external libraries dynamically
   linked.

   The -W command describes the environment used to build Kea. This command
   displays a copy of the config.report file produced by ./configure that is
   embedded in the executable binary.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/dhcp4/.libs/kea-dhcp4.

 strings path/kea-dhcp4 | sed -n 's/;;;; //p'

   When running in a console, the server can be shut down by pressing ctrl-c.
   It detects the key combination and shuts down gracefully.

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file.

   Since the DHCPv4 server opens privileged ports, it requires root access.
   Make sure you run this daemon as root.

   During startup the server will attempt to create a PID file of the form:
   [localstatedir]/[conf name].kea-dhcp4.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP4_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

7.2. DHCPv4 Server Configuration

  7.2.1. Introduction

   This section explains how to configure the DHCPv4 server using the Kea
   configuration backend. (Kea configuration using any other backends is
   outside of scope of this document.) Before DHCPv4 is started, its
   configuration file has to be created. The basic configuration is as
   follows:

 {
 # DHCPv4 configuration starts in this line
 "Dhcp4": {

 # First we set up global values
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp4.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.1 - 192.0.2.200" }
             ]
         }
     ]

 # DHCPv4 configuration ends with this line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example and their format. Subsequent sections of this chapter go
   into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration consists of one or more objects. In
   this specific example, we have only one object called Dhcp4. This is a
   simplified configuration, as usually there will be additional objects,
   like Logging or DhcpDns, but we omit them now for clarity. The Dhcp4
   configuration starts with the "Dhcp4": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp4 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that the
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may also require moving the comma. The second caveat is that
   it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv4 configuration elements, the very first few elements
   define some global parameters. valid-lifetime defines for how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   renew-timer and rebind-timer are values that define T1 and T2 timers that
   govern when the client will begin the renewal and rebind procedures. Note
   that renew-timer and rebind-timer are optional. If they are not specified
   the client will select values for T1 and T2 timers according to the RFC
   2131.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually, lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example -- type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters follow, a
   trailing comma is present.

   Finally, we need to define a list of IPv4 subnets. This is the most
   important DHCPv4 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet4 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At a minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pools (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet4 parameter would be specified and
   separated by commas. For example, to define three subnets, the following
   syntax would be used:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24"
     },
     {
         "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
         "subnet": "192.0.3.0/24"
     },
     {
         "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
         "subnet": "192.0.4.0/24"
     }
 ]

   After all parameters are specified, we have two contexts open: global and
   Dhcp4, hence we need two closing curly brackets to close them. In a real
   life configuration file there most likely would be additional components
   defined such as Logging or DhcpDdns, so the closing brace would be
   followed by a comma and another object definition.

  7.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are three database backends available: memfile (which is
   the default backend), MySQL and PostgreSQL.

    7.2.2.1. Memfile, Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 7.2.2.2,
   "Lease Database Configuration" describes this option. In typical smaller
   deployments though, the server will use a CSV file rather than a database
   to store lease information. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp4/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list presents the remaining, not mandatory parameters, which can
   be used to configure the Memfile backend.

     * persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     * name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases4.csv" .
     * lfc-interval: specifies the interval in seconds, at which the server
       (Memfile backend) will perform a lease file cleanup (LFC), which
       removes the redundant (historical) information from the lease file and
       effectively reduces the lease file size. The cleanup process is
       described in more detailed fashion further in this section. The
       default value of the lfc-interval is 0, which disables the LFC.

   The example configuration of the Memfile backend is presented below:

 "Dhcp4": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases4.csv",
         "lfc-interval": 1800
     }
 }

   This configuration selects the /tmp/kea-leases4.csv as the storage for
   lease information and enables persistence (writing lease updates to this
   file). It also configures the backend perform the periodic cleanup of the
   lease files, executed every 30 minutes.

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time when
   the server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not supersede the existing client's lease, as it
   would require the lookup of the specific lease entry, but simply appends
   the new lease information at the end of the lease file. The previous lease
   entries for the client are not removed. When the server loads leases from
   the lease file, e.g. at the server startup, it assumes that the latest
   lease entry for the client is the valid one. The previous entries are
   discarded. This means that the server can re-construct the accurate
   information about the leases even though there may be many lease entries
   for each client. However, storing many entries for each client results in
   bloated lease file and impairs the performance of the server's startup and
   reconfiguration, as it needs to process larger number of lease entries.

   The lease file cleanup removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   renewals are, the lesser value of the lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But, this implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server, which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for completing
   the cleanup before the new cleanup is triggered.

   The LFC is performed by a separate process (in background) to avoid
   performance impact on the server process. In order to avoid the conflicts
   between the two processes both using the same lease files, the LFC process
   operates on the copy of the original lease file, rather than on the lease
   file used by the server to record lease updates. There are also other
   files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located on the Kea wiki:
   http://kea.isc.org/wiki/LFCDesign.

    7.2.2.2. Lease Database Configuration

  Note

   Lease database access information must be configured for the DHCPv4
   server, even if it has already been configured for the DHCPv6 server. The
   servers store their information independently, so each server can use a
   separate database or both servers can use the same database.

   Lease database configuration is controlled through the
   Dhcp4/lease-database parameters. The type of the database must be set to
   "memfile", "mysql" or "postgresql", e.g.

 "Dhcp4": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the leases must be set: this is the
   name used when the lease database was created (see Section 4.3.2.1, "First
   Time Creation of Kea Database" or Section 4.3.3.1, "Manually Create the
   PostgreSQL Database and the Kea User").

 "Dhcp4": { "lease-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system to the DHCPv4 server, the
   database host name must also be specified (although it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp4": { "lease-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv4 server. In this case, set the value to the empty
   string:

 "Dhcp4": { "lease-database": { "host" : "", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp4": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

  7.2.3. Hosts Storage

  Note

   This feature did not undergo the regular system level testing conducted by
   ISC. As such, please treat it as experimental.

   Kea is also able to store information about host reservations in the
   database. Hosts database configuration uses the same syntax as lease
   database. In fact, Kea server opens independent connections for each
   purpose, be it lease or hosts information. This gives the solution most
   flexibility. Kea can be used to keep leases and host reservations
   separately, but can also point to the same database. Currently the only
   supported hosts database type is MySQL.

   Please note that usage of hosts storage is optional. User can define all
   host reservations in the configuration file. That is the recommended way
   if the number of reservations is small. However, with the number of
   reservations growing it's more convenient to use host storage. Please note
   that both storages (configuration file and MySQL) can be used together. If
   hosts are defined in both places, the definitions from configuration file
   are checked first and external storage is checked later, if necessary.

   All hosts leases issued by the server are stored in the hosts database.
   Currently there is only one available backend: MySQL. Other host backends
   will become available in future Kea versions.

    7.2.3.1. IPv4 Hosts Database Configuration

   Hosts database configuration is controlled through the
   Dhcp4/hosts-database parameters. If enabled, the type of the database must
   be set to "mysql". Other hosts backends may be added in later Kea
   versions.

 "Dhcp4": { "hosts-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the leases must be set: this is the
   name used when the lease database was created (see Section 4.3.2.1, "First
   Time Creation of Kea Database").

 "Dhcp4": { "hosts-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system to the DHCPv4 server, the
   database host name must also be specified (although it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp4": { "hosts-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv4 server. In this case, set the value to the empty
   string:

 "Dhcp4": { "hosts-database": { "host" : "", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp4": { "hosts-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

  7.2.4. Interface configuration

   The DHCPv4 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration tells the server
   to listen on all available interfaces:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 },


   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   explicit interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this form of usage will only be used when it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

   Some deployments of the DHCP servers require that the servers listen on
   the interfaces with multiple IPv4 addresses configured. In these
   situations, the address to use can be selected by appending an IPv4
   address to the interface name in the following manner:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]
     },
     ...
 }


   If it is desired that the server listens on multiple IPv4 addresses
   assigned to the same interface, multiple addresses can be specified for
   this interface as in the example below:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth1/10.0.0.2" ]
     },
     ...
 }


   Alternatively, if the server should listen on all addresses for the
   particular interface, an interface name without any address should be
   specified.

   Kea supports responding to directly connected clients which don't have an
   address configured on the interface yet. This requires that the server
   injects the hardware address of the destination into the data link layer
   of the packet being sent to the client. The DHCPv4 server utilizes the raw
   sockets to achieve this, and builds the entire IP/UDP stack for the
   outgoing packets. The down side of raw socket use, however, is that
   incoming and outgoing packets bypass the firewalls (e.g. iptables). It is
   also troublesome to handle traffic on multiple IPv4 addresses assigned to
   the same interface, as raw sockets are bound to the interface and advanced
   packet filtering techniques (e.g. using the BPF) have to be used to
   receive unicast traffic on the desired addresses assigned to the
   interface, rather than capturing whole traffic reaching the interface to
   which the raw socket is bound. Therefore, in the deployments where the
   server doesn't have to provision the directly connected clients and only
   receives the unicast packets from the relay agents, it is desired to
   configure the DHCP server to utilize the IP/UDP datagram sockets, instead
   of raw sockets. The following configuration demonstrates how this can be
   achieved:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "dhcp-socket-type": "udp"
     },
     ...
 }


   The dhcp-socket-type specifies that the IP/UDP sockets will be opened on
   all interfaces on which the server listens, i.e. "eth1" and "eth3" in our
   case. If the dhcp-socket-type is set to raw, it configures the server to
   use raw sockets instead. If the dhcp-socket-type value is not specified,
   the default value raw is used.

   Using UDP sockets automatically disables the reception of broadcast
   packets from directly connected clients. This effectively means that the
   UDP sockets can be used for relayed traffic only. When using the raw
   sockets, both the traffic from the directly connected clients and the
   relayed traffic will be handled. Caution should be taken when configuring
   the server to open multiple raw sockets on the interface with several IPv4
   addresses assigned. If the directly connected client sends the message to
   the broadcast address all sockets on this link will receive this message
   and multiple responses will be sent to the client. Hence, the
   configuration with multiple IPv4 addresses assigned to the interface
   should not be used when the directly connected clients are operating on
   that link. To use a single address on such interface, the
   "interface-name/address" notation should be used.

  Note

   Specifying the value raw as the socket type, doesn't guarantee that the
   raw sockets will be used! The use of raw sockets to handle the traffic
   from the directly connected clients is currently supported on Linux and
   BSD systems only. If the raw sockets are not supported on the particular
   OS, the server will issue a warning and fall back to use the IP/UDP
   sockets.

  7.2.5. Issues with unicast responses to DHCPINFORM

   The use of UDP sockets has certain benefits in deployments where the
   server receives only relayed traffic. These benefits are mentioned in the
   Section 7.2.4, "Interface configuration". From the administrator's
   perspective it is often desired to be able to configure the system's
   firewall to filter out the unwanted traffic, and the use of UDP sockets
   facilitates it. However, the administrator must also be aware of the
   implications related to filtering certain types of traffic as it may
   impair the DHCP server's operation.

   In this section we are focusing on the case when the server receives the
   DHCPINFORM message from the client via a relay. According to the RFC 2131,
   the server should unicast the DHCPACK response to the address carried in
   the 'ciaddr' field. When the UDP socket is in use, the DHCP server relies
   on the low level functions of an operating system to build the data link,
   IP and UDP layers of the outgoing message. Typically, the OS will first
   use ARP to obtain the client's link layer address to be inserted into the
   frame's header, if the address is not cached from a previous transaction
   that the client had with the server. When the ARP exchange is successful,
   the DHCP message can be unicast to the client, using the obtained address.

   Some system administrators block ARP messages in their network, which
   causes issues for the server when it responds to the DHCPINFORM messages,
   because the server is unable to send the DHCPACK if the preceding ARP
   communication fails. Since the OS is entirely responsible for the ARP
   communication and then sending the DHCP packet over the wire, the DHCP
   server has no means to determine that the ARP exchange failed and the DHCP
   response message was dropped. Thus, the server does not log any error
   messages when the outgoing DHCP response is dropped. At the same time, all
   hooks pertaining to the packet sending operation will be called, even
   though the message never reaches its destination.

   Note that the issue described in this section is not observed when the raw
   sockets are in use, because, in this case, the DHCP server builds all the
   layers of the outgoing message on its own and does not use ARP. Instead,
   it inserts the value carried in the 'chaddr' field of the DHCPINFORM
   message into the link layer.

   Server administrators willing to support DHCPINFORM messages via relays
   should not block ARP traffic in their networks or should use raw sockets
   instead of UDP sockets.

  7.2.6. IPv4 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with their
   respective subnets. When a subnet identifier is not specified for a subnet
   being configured, it will be automatically assigned by the configuration
   mechanism. The identifiers are assigned from 1 and are monotonically
   increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, something that may have unexpected
   consequences. It is planned to implement a mechanism to preserve
   auto-generated subnet ids in a future version of Kea. However, the only
   remedy for this issue at present is to manually specify a unique
   identifier for each subnet.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  7.2.7. Configuration of IPv4 Address Pools

   The essential role of DHCPv4 server is address assignment. The server has
   to be configured with at least one subnet and one pool of dynamic
   addresses to be managed. For example, assume that the server is connected
   to a network segment that uses the 192.0.2.0/24 prefix. The Administrator
   of that network has decided that addresses from range 192.0.2.10 to
   192.0.2.20 are going to be managed by the Dhcp4 server. Such a
   configuration can be achieved in the following way:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10 - 192.0.2.20" }
             ],
             ...
         }
     ]
 }

   Note that subnet is defined as a simple string, but the pools parameter is
   actually a list of pools: for this reason, the pools definition is
   enclosed in square brackets, even though only one range of addresses is
   specified in this example.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 192.0.2.64/26 should be also be
   managed by the server. It could be written as 192.0.2.64 to 192.0.2.127.
   Alternatively, it can be expressed more simply as 192.0.2.64/26. Both
   formats are supported by Dhcp4 and can be mixed in the pool list. For
   example, one could define the following pools:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10-192.0.2.20" },
                 { "pool": "192.0.2.64/26" }
             ],
             ...
         }
     ],
     ...
 }

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible. White space in pool definitions is
   ignored, so spaces before and after the hyphen are optional. They can be
   used to improve readability.

   The server may be configured to serve more than one subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
             ...
         },
         {
             "subnet": "192.0.3.0/24",
             "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
             ...
         },
         {
             "subnet": "192.0.4.0/24",
             "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
             ...
         }
     ]
 }

   When configuring a DHCPv4 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) and the last (typically broadcast address) address from
   that pool. In the aforementioned example of pool 192.0.3.0/24, both
   192.0.3.0 and 192.0.3.255 addresses may be assigned as well. This may be
   invalid in some network configurations. If you want to avoid this, please
   use the "min-max" notation.

  7.2.8. Standard DHCPv4 options

   One of the major features of the DHCPv4 server is to provide configuration
   options to clients. Most of the options are sent by the server, only if
   the client explicitly requests them using the Parameter Request List
   option. Those that do not require being requested using the Parameter
   Request List option are commonly used options, e.g. "Domain Server", and
   options which require special behavior, e.g. "Client FQDN" is returned to
   the client if the client has included this option in its message to the
   server.

   The Table 7.1, "List of standard DHCPv4 options" comprises the list of the
   standard DHCPv4 options, whose values can be configured using the
   configuration structures described in this section. This table excludes
   the options which require special processing and thus cannot be configured
   with some fixed values. The last column of this table specifies which
   options can be sent by the server even when they are not requested in the
   Parameter Request list option, and which are sent only when explicitly
   requested. These options are marked with the values 'true' and 'false'
   respectively.

   The following example shows how to configure the addresses of DNS servers,
   which is one of the most frequently used options. Options specified in
   this way are considered global and apply to all configured subnets.

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
            "csv-format": true,
            "data": "192.0.2.1, 192.0.2.2"
         },
         ...
     ]
 }

   The name parameter specifies the option name. For a list of currently
   supported names, see Table 7.1, "List of standard DHCPv4 options" below.
   The code parameter specifies the option code, which must match one of the
   values from that list. The next line specifies the option space, which
   must always be set to "dhcp4" as these are standard DHCPv4 options. For
   other option spaces, including custom option spaces, see Section 7.2.11,
   "Nested DHCPv4 Options (Custom Option Spaces)". The next line specifies
   the format in which the data will be entered: use of CSV (comma separated
   values) is recommended. The sixth line gives the actual value to be sent
   to clients. Data is specified as normal text, with values separated by
   commas if more than one value is allowed.

   Options can also be configured as hexadecimal values. If csv-format is set
   to false, option data must be specified as a hexadecimal string. The
   following commands configure the domain-name-servers option for all
   subnets with the following addresses: 192.0.3.1 and 192.0.3.2. Note that
   csv-format is set to false.

 "Dhcp4": {
     "option-data": [
         {
             "name": "domain-name-servers",
             "code": 6,
             "space": "dhcp4",
             "csv-format": false,
             "data": "C0 00 03 01 C0 00 03 02"
         },
         ...
     ],
     ...
 }

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 7.2.12,
   "Unspecified parameters for DHCPv4 option configuration".

   It is possible to specify or override options on a per-subnet basis. If
   clients connected to most of your subnets are expected to get the same
   values of a given option, you should use global options: you can then
   override specific values for a small number of subnets. On the other hand,
   if you use different values in each subnet, it does not make sense to
   specify global option values (Dhcp4/option-data), rather you should set
   only subnet-specific values (Dhcp4/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 192.0.2.3.

 "Dhcp4": {
     "subnet4": [
         {
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   The currently supported standard DHCPv4 options are listed in Table 7.1,
   "List of standard DHCPv4 options" and Table 7.2, "List of standard DHCPv4
   options (continued)". The "Name" and "Code" are the values that should be
   used as a name in the option-data structures. "Type" designates the format
   of the data: the meanings of the various types is given in Table 7.3,
   "List of standard DHCP option types".

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option time-servers
   allows the specification of more than one IPv4 address, so allowing
   clients to obtain the addresses of multiple NTP servers.

   The Section 7.2.9, "Custom DHCPv4 options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea does not provide a definition yet. In order to use such options, a
   server administrator must create a definition as described in
   Section 7.2.9, "Custom DHCPv4 options" in the 'dhcp4' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism will allow any option format as it has no
   means to validate the format at the moment.

   Table 7.1. List of standard DHCPv4 options

   +-------------------------------------------------------------------------+
   |                             |      |              |        |Returned if |
   |            Name             | Code |     Type     | Array? |    not     |
   |                             |      |              |        | requested? |
   |-----------------------------+------+--------------+--------+------------|
   |time-offset                  |  2   |    int32     | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |routers                      |  3   | ipv4-address |  true  |    true    |
   |-----------------------------+------+--------------+--------+------------|
   |time-servers                 |  4   | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |name-servers                 |  5   | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |domain-name-servers          |  6   | ipv4-address |  true  |    true    |
   |-----------------------------+------+--------------+--------+------------|
   |log-servers                  |  7   | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |cookie-servers               |  8   | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |lpr-servers                  |  9   | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |impress-servers              |  10  | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |resource-location-servers    |  11  | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |boot-size                    |  13  |    uint16    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |merit-dump                   |  14  |    string    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |domain-name                  |  15  |     fqdn     | false  |    true    |
   |-----------------------------+------+--------------+--------+------------|
   |swap-server                  |  16  | ipv4-address | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |root-path                    |  17  |    string    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |extensions-path              |  18  |    string    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |ip-forwarding                |  19  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |non-local-source-routing     |  20  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |policy-filter                |  21  | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |max-dgram-reassembly         |  22  |    uint16    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |default-ip-ttl               |  23  |    uint8     | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |path-mtu-aging-timeout       |  24  |    uint32    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |path-mtu-plateau-table       |  25  |    uint16    |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |interface-mtu                |  26  |    uint16    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |all-subnets-local            |  27  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |broadcast-address            |  28  | ipv4-address | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |perform-mask-discovery       |  29  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |mask-supplier                |  30  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |router-discovery             |  31  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |router-solicitation-address  |  32  | ipv4-address | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |static-routes                |  33  | ipv4-address |  true  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |trailer-encapsulation        |  34  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |arp-cache-timeout            |  35  |    uint32    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |ieee802-3-encapsulation      |  36  |   boolean    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |default-tcp-ttl              |  37  |    uint8     | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |tcp-keepalive-interval       |  38  |    uint32    | false  |   false    |
   |-----------------------------+------+--------------+--------+------------|
   |tcp-keepalive-garbage        |  39  |   boolean    | false  |   false    |
   +-------------------------------------------------------------------------+

   Table 7.2. List of standard DHCPv4 options (continued)

   +-------------------------------------------------------------------------+
   |                           |    |                     |      |Returned if|
   |           Name            |Code|        Type         |Array?|    not    |
   |                           |    |                     |      |requested? |
   |---------------------------+----+---------------------+------+-----------|
   |nis-domain                 | 40 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |nis-servers                | 41 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |ntp-servers                | 42 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |vendor-encapsulated-options| 43 |        empty        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |netbios-name-servers       | 44 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |netbios-dd-server          | 45 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |netbios-node-type          | 46 |        uint8        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |netbios-scope              | 47 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |font-servers               | 48 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |x-display-manager          | 49 |    ipv4-address     | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |dhcp-option-overload       | 52 |        uint8        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |dhcp-message               | 56 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |dhcp-max-message-size      | 57 |       uint16        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |vendor-class-identifier    | 60 |       binary        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |nwip-domain-name           | 62 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |nwip-suboptions            | 63 |       binary        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |tftp-server-name           | 66 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |boot-file-name             | 67 |       string        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |user-class                 | 77 |       binary        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |client-system              | 93 |       uint16        | true |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |client-ndi                 | 94 |record (uint8, uint8,|false |   false   |
   |                           |    |       uint8)        |      |           |
   |---------------------------+----+---------------------+------+-----------|
   |uuid-guid                  | 97 |   record (uint8,    |false |   false   |
   |                           |    |       binary)       |      |           |
   |---------------------------+----+---------------------+------+-----------|
   |subnet-selection           |118 |    ipv4-address     |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |domain-search              |119 |       binary        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |vivco-suboptions           |124 |       binary        |false |   false   |
   |---------------------------+----+---------------------+------+-----------|
   |vivso-suboptions           |125 |       binary        |false |   false   |
   +-------------------------------------------------------------------------+

   Table 7.3. List of standard DHCP option types

   +------------------------------------------------------------------------+
   |     Name     |                         Meaning                         |
   |--------------+---------------------------------------------------------|
   | binary       | An arbitrary string of bytes, specified as a set of     |
   |              | hexadecimal digits.                                     |
   |--------------+---------------------------------------------------------|
   | boolean      | Boolean value with allowed values true or false         |
   |--------------+---------------------------------------------------------|
   | empty        | No value, data is carried in suboptions                 |
   |--------------+---------------------------------------------------------|
   | fqdn         | Fully qualified domain name (e.g. www.example.com)      |
   |--------------+---------------------------------------------------------|
   | ipv4-address | IPv4 address in the usual dotted-decimal notation (e.g. |
   |              | 192.0.2.1)                                              |
   |--------------+---------------------------------------------------------|
   | ipv6-address | IPv6 address in the usual colon notation (e.g.          |
   |              | 2001:db8::1)                                            |
   |--------------+---------------------------------------------------------|
   | record       | Structured data that may comprise any types (except     |
   |              | "record" and "empty")                                   |
   |--------------+---------------------------------------------------------|
   | string       | Any text                                                |
   |--------------+---------------------------------------------------------|
   | uint8        | 8 bit unsigned integer with allowed values 0 to 255     |
   |--------------+---------------------------------------------------------|
   | uint16       | 16 bit unsigned integer with allowed values 0 to 65535  |
   |--------------+---------------------------------------------------------|
   | uint32       | 32 bit unsigned integer with allowed values 0 to        |
   |              | 4294967295                                              |
   +------------------------------------------------------------------------+

  7.2.9. Custom DHCPv4 options

   Kea supports custom (non-standard) DHCPv4 options. Assume that we want to
   define a new DHCPv4 option called "foo" which will have code 222 and will
   convey a single unsigned 32 bit integer value. We can define such an
   option by using the following entry in the configuration file:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 222,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp4",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The false value of the array parameter determines that the option does NOT
   comprise an array of "uint32" values but rather a single value. Two other
   parameters have been left blank: record-types and encapsulate. The former
   specifies the comma separated list of option data fields if the option
   comprises a record of data fields. This should be non-empty if the type is
   set to "record". Otherwise it must be left blank. The latter parameter
   specifies the name of the option space being encapsulated by the
   particular option. If the particular option does not encapsulate any
   option space it should be left blank. Note that the above set of comments
   define the format of the new option and do not set its values.

   The name, code and type parameters are required, all others are optional.
   The array default value is false. The record-types and encapsulate default
   values are blank (i.e. ""). The default space is "dhcp4".

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "code": 222,
             "space": "dhcp4",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv4-address etc): it is possible to define an option
   comprising a number of existing primitives. Assume we want to define a new
   option that will consist of an IPv4 address, followed by an unsigned 16
   bit integer, followed by a boolean value, followed by a text string. Such
   an option could be defined in the following way:

 "Dhcp4": {
     "option-def": [
         {
             "name": "bar",
             "code": 223,
             "space": "dhcp4",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The type is set to "record" to indicate that the option contains multiple
   values of different types. These types are given as a comma-separated list
   in the record-types field and should be those listed in Table 7.3, "List
   of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp4": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp4",
             "code": 223,
             "csv-format": true,
             "data": "192.0.2.100, 123, true, Hello World"
         }
     ],
     ...
 }

   csv-format is set to true to indicate that the data field comprises a
   command-separated list of values. The values in the data must correspond
   to the types set in the record-types field of the option definition.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future Kea versions will accept all those
   values for all boolean parameters.

  7.2.10. DHCPv4 Vendor Specific Options

   Currently there are two option spaces defined for the DHCPv4 daemon:
   "dhcp4" (for the top level DHCPv4 options) and
   "vendor-encapsulated-options-space", which is empty by default but options
   can be defined in it. Those options will be carried in the Vendor Specific
   Information option (code 43). The following examples show how to define an
   option "foo", with code 1, that consists of an IPv4 address, an unsigned
   16 bit integer and a string. The "foo" option is conveyed in a Vendor
   Specific Information option.

   The first step is to define the format of the option:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-encapsulated-options-space",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, string",
             "encapsulate": ""
         }
     ],
     ...
 }

   (Note that the option space is set to
   "vendor-encapsulated-options-space".) Once the option format is defined,
   the next step is to define actual values for that option:

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-encapsulated-options-space",
             "code": 1,
             "csv-format": true,
             "data": "192.0.2.3, 123, Hello World"
         }
     ],
     ...
 }

   We also include the Vendor Specific Information option, the option that
   conveys our sub-option "foo". This is required, else the option will not
   be included in messages sent to the client.

 "Dhcp4": {
     "option-data": [
         {
             "name": "vendor-encapsulated-options"
         }
     ],
     ...
 }

   Alternatively, the option can be specified using its code.

 "Dhcp4": {
     "option-data": [
         {
             "code": 43
         }
     ],
     ...
 }

  7.2.11. Nested DHCPv4 Options (Custom Option Spaces)

   It is sometimes useful to define completely new option space. This is the
   case when user creates new option in the standard option space ("dhcp4")
   and wants this option to convey sub-options. Since they are in a separate
   space, sub-option codes will have a separate numbering scheme and may
   overlap with the codes of standard options.

   Note that creation of a new option space when defining sub-options for a
   standard option is not required, because it is created by default if the
   standard option is meant to convey any sub-options (see Section 7.2.10,
   "DHCPv4 Vendor Specific Options").

   Assume that we want to have a DHCPv4 option called "container" with code
   222 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp4": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv4-address",
             "record-types": "",
             "array": false,
             "encapsulate ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv4 option with our desired code
   and specify that it should include options from the new option space:

 "Dhcp4": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 222,
             "space": "dhcp4",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the "encapsulate" field. The "type" field is set to "empty" to indicate
   that this option does not carry any data other than sub-options.

   Finally, we can set values for the new options:

 "Dhcp4": {
     "option-data": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "data": "192.0.2.3"
         },
         }
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "data": "Hello world"
         },
         {
             "name": "container",
             "code": 222,
             "space": "dhcp4"
         }
     ],
     ...
 }

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the "type" value
   would have to be set to "uint16" in the option definition. (Such an option
   would then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the "data" parameter -- which
   should be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  7.2.12. Unspecified parameters for DHCPv4 option configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values may be used. However, it is important
   to understand the implications of not specifying some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     * name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     * code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     * space - if the option space is unspecified it will default to 'dhcp4'
       which is an option space holding DHCPv4 standard options.
     * data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which spec allows
       for the length of 0. For such options, the data parameter may be
       omitted in the configuration.
     * csv-format - if this value is not specified and the definition for the
       particular option exists, the server will assume that the option data
       is specified as a list of comma separated values to be assigned to
       individual fields of the DHCP option. If the definition does not exist
       for this option, the server will assume that the data parameter
       contains the option payload in the binary format (represented as a
       string of hexadecimal digits). Note that not specifying this parameter
       doesn't imply that it defaults to a fixed value, but the configuration
       data interpretation also depends on the presence of the option
       definition. An administrator must be aware if the definition for the
       particular option exists when this parameter is not specified. It is
       generally recommended to not specify this parameter only for the
       options for which the definition exists, e.g. standard options.
       Setting csv-format to an explicit value will cause the server to
       strictly check the format of the option data specified.

  7.2.13. Stateless Configuration of DHCPv4 clients

   The DHCPv4 server supports the stateless client configuration whereby the
   client has an IP address configured (e.g. using manual configuration) and
   only contacts the server to obtain other configuration parameters, e.g.
   DNS servers' addresses. In order to obtain the stateless configuration
   parameters the client sends the DHCPINFORM message to the server with the
   "ciaddr" set to the address that the client is currently using. The server
   unicasts the DHCPACK message to the client that includes the stateless
   configuration ("yiaddr" not set).

   The server will respond to the DHCPINFORM when the client is associated
   with the particular subnet defined in the server's configuration. The
   example subnet configuration will look like this:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24"
             "option-data": [ {
                 "name": "domain-name-servers",
                 "code": 6,
                 "data": "192.0.2.200,192.0.2.201",
                 "csv-format": true,
                 "space": "dhcp4"
             } ]
         }
     ]
 }

   This subnet specifies the single option which will be included in the
   DHCPACK message to the client in response to DHCPINFORM. Note that the
   subnet definition does not require the address pool configuration if it
   will be used solely for the stateless configuration.

   This server will associate the subnet with the client if one of the
   following conditions is met:

     * The DHCPINFORM is relayed and the giaddr matches the configured
       subnet.
     * The DHCPINFORM is unicast from the client and the ciaddr matches the
       configured subnet.
     * The DHCPINFORM is unicast from the client, the ciaddr is not set but
       the source address of the IP packet matches the configured subnet.
     * The DHCPINFORM is not relayed and the IP address on the interface on
       which the message is received matches the configured subnet.

  7.2.14. Client Classification in DHCPv4

   The DHCPv4 server includes support for client classification. At the
   current time the capabilities of the classification process are limited
   but it is expected they will be expanded in the future. For a deeper
   discussion of the classification process see Chapter 12, Client
   Classification.

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. It is envisaged that client
   classification will be used for changing the behavior of almost any part
   of the DHCP message processing, including the assignment of leases from
   different pools, the assignment of different options (or different values
   of the same options) etc. In the current release of the software however,
   there are only three mechanisms that take advantage of client
   classification: subnet selection, assignment of different options, and,
   for cable modems, there are specific options for use with the TFTP server
   address and the boot file field.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario is cable
   networks. There are two classes of devices: the cable modem itself, which
   should be handed a lease from subnet A and all other devices behind the
   modem that should get a lease from subnet B. That segregation is essential
   to prevent overly curious users from playing with their cable modems. For
   details on how to set up class restrictions on subnets, see Section 12.5,
   "Configuring Subnets With Class Information".

   The process of doing classification is conducted in three steps. The first
   step is to assess an incoming packet and assign it to zero or more
   classes. The second step is to choose a subnet, possibly based on the
   class information. The third step is to assign options again possibly
   based on the class information.

   There are two methods of doing classification. The first is automatic and
   relies on examining the values in the vendor class options. Information
   from these options is extracted and a class name is constructed from it
   and added to the class list for the packet. The second allows you to
   specify an expression that is evaluated for each packet. If the result is
   true the packet is a member of the class.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

    7.2.14.1. Using Vendor Class Information in Classification

   The server checks whether an incoming packet includes the vendor class
   identifier option (60). If it does, the content of that option is
   prepended with "VENDOR_CLASS_" then it is interpreted as a class. For
   example, modern cable modems will send this option with value "docsis3.0"
   and as a result the packet will belong to class "VENDOR_CLASS_docsis3.0".

   For clients that belong to the VENDOR_CLASS_docsis3.0 class, the siaddr
   field is set to the value of next-server (if specified in a subnet). If
   there is a boot-file-name option specified, its value is also set in the
   file field in the DHCPv4 packet. For eRouter1.0 class, the siaddr is
   always set to 0.0.0.0. That capability is expected to be moved to an
   external hook library that will be dedicated to cable modems.

   This example shows a configuration using an automatically generated
   "VENDOR_CLASS_" class. The Administrator of the network has decided that
   addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed by
   the Dhcp4 server and only clients belonging to the docsis3.0 client class
   are allowed to use that pool.

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "VENDOR_CLASS_docsis3.0"
         }
     ],
     ...
 }

    7.2.14.2. Defining and Using Custom Classes

   The following example shows how to configure a class using an expression
   and a subnet making use of that class. This configuration defines the
   class named "Client_foo". It is comprised of all clients who's client ids
   (option 61) start with the string "foo". Members of this class will be
   given addresses from 192.0.2.10 to 192.0.2.20 and 192.0.2.1 and 192.0.2.2
   as their domain name servers. For a deeper discussion of the
   classification process see Chapter 12, Client Classification.

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "Client_foo"
         },
         ...
     ],
     ...
 }

  7.2.15. Configuring DHCPv4 for DDNS

   As mentioned earlier, kea-dhcp4 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2" ) to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (A records), reverse
       DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters for controlling the generation of NCRs for submission to D2
   are contained in the dhcp-ddns section of the kea-dhcp4 server
   configuration. The mandatory parameters for the DHCP DDNS configuration
   are enable-updates which is unconditionally required, and
   qualifying-suffix which has no default value and is required when
   enable-updates is set to true. The two (disabled and enabled) minimal DHCP
   DDNS configurations are:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     * "server-ip": "127.0.0.1"
     * "server-port": 53001
     * "sender-ip": ""
     * "sender-port": 0
     * "max-queue-size": 1024
     * "ncr-protocol": "UDP"
     * "ncr-format": "JSON"
     * "override-no-update": false
     * "override-client-update": false
     * "replace-client-name": false
     * "generated-prefix": "myhost"

    7.2.15.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp4 must be able to
   communicate with it. kea-dhcp4 uses the following configuration parameters
   to control how it communications with D2:

     * enable-updates - determines whether or not kea-dhcp4 will generate
       NCRs. By default, this value is false hence DDNS updates are disabled.
       To enable DDNS updates set this value to true:
     * server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * server-port - port on which D2 listens for requests. The default value
       is 53001.
     * sender-ip - IP address which kea-dhcp4 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp4 to select a
       suitable address.
     * sender-port - port which kea-dhcp4 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp4 to select a suitable port.
     * max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intention is to allow the kea-dhcp4
       server to continue lease operations without running the risk that its
       memory usage grows without limit. The default value is 1024.
     * ncr-protocol - socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     * ncr-format - packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to be running on the same machine as
   kea-dhcp4, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must be altered accordingly. For example, if
   D2 has been configured to listen on 192.168.1.10 port 900, the following
   configuration would be required:

 "Dhcp4": {
     "dhcp-ddns": {
         "server-ip": "192.168.1.10",
         "server-port": 900,
         ...
     },
     ...
 }

    7.2.15.2. When Does the kea-dhcp4 Server Generate DDNS Requests?

   kea-dhcp4 follows the behavior prescribed for DHCP servers in RFC 4702. It
   is important to keep in mind that kea-dhcp4 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are within the purview of D2 itself
   (Chapter 10, The DHCP-DDNS Server). This section describes when kea-dhcp4
   will generate NCRs and the configuration parameters that can be used to
   influence this decision. It assumes that the "enable-updates" parameter is
   true.

   In general, kea-dhcp4 will generate DDNS update requests when:

    1. A new lease is granted in response to a DHCP REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a DHCP RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made. The decision making
   involved when granting a new lease (the first case) is more involved and
   is discussed next.

   When a new lease is granted, kea-dhcp4 will generate a DDNS update request
   if the DHCP REQUEST contains either the FQDN option (code 81) or the Host
   Name option (code 12). If both are present, the server will use the FQDN
   option. By default kea-dhcp4 will respect the FQDN N and S flags specified
   by the client as shown in the following table:

   Table 7.4. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp4 will honor the
   client's wishes and generate a DDNS request to the DHCP-DDNS server to
   update only reverse DNS data. The parameter override-client-update can be
   used to instruct the server to override client delegation requests. When
   this parameter is true, kea-dhcp4 will disregard requests for client
   delegation and generate a DDNS request to update both forward and reverse
   DNS data. In this case, the N-S-O flags in the server's response to the
   client will be 0-1-1 respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp4.)

   To override client delegation, set the following values in your
   configuration file:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, override-no-update,
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp4 will generate a DDNS update request to
   kea-dhcp-ddns even if the client requests that no updates be done. The
   N-S-O flags in the server's response to the client will be 0-1-1.

   To override client delegation, the following values should be set in your
   configuration:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

   kea-dhcp4 will always generate DDNS update requests if the client request
   only contains the Host Name option. In addition it will include an FQDN
   option in the response to the client with the FQDN N-S-O flags set to
   0-1-0 respectively. The domain name portion of the FQDN option will be the
   name submitted to D2 in the DDNS update request.

    7.2.15.3. kea-dhcp4 name generation for DDNS update requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp4 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client in the DHCP REQUEST.

   The rules for determining the FQDN option are as follows:

    1. If configured to do, so ignore the DHCPREQUEST contents and generate a
       FQDN using a configurable prefix and suffix.

    2. If the DHCPREQUEST contains the client FQDN option, the candidate name
       is taken from there, otherwise it is taken from the Host Name option.
       The candidate name may then be modified:

         a. If the candidate name is a fully qualified domain name, use it.

         b. If the candidate name is a partial (i.e. unqualified) name then
            add a configurable suffix to the name and use the result as the
            FQDN.

         c. If the candidate name is a empty, generate a FQDN using a
            configurable prefix and suffix.

   To instruct kea-dhcp4 to always generate the FQDN for a client, set the
   parameter replace-client-name to true as follows:

 "Dhcp4": {
     "dhcp-ddns": {
         "replace-client-name": true,
         ...
     },
     ...
 }

   The prefix used in the generation of a FQDN is specified by the
   generated-prefix parameter. The default value is "myhost". To alter its
   value simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating a FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When generating a name, kea-dhcp4 will construct name of the format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if the lease address is 172.16.1.10, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-172-16-1-10.example.com.

  7.2.16. Next Server (siaddr)

   In some cases, clients want to obtain configuration from the TFTP server.
   Although there is a dedicated option for it, some devices may use the
   siaddr field in the DHCPv4 packet for that purpose. That specific field
   can be configured using next-server directive. It is possible to define it
   in the global scope or for a given subnet only. If both are defined, the
   subnet value takes precedence. The value in subnet can be set to 0.0.0.0,
   which means that next-server should not be sent. It may also be set to an
   empty string, which means the same as if it was not defined at all, i.e.
   use the global value.

 "Dhcp4": {
     "next-server": "192.0.2.123",
     ...,
     "subnet4": [
         {
             "next-server": "192.0.2.234",
             ...
         }
     ]
 }

  7.2.17. Echoing Client-ID (RFC 6842)

   The original DHCPv4 specification (RFC 2131) states that the DHCPv4 server
   must not send back client-id options when responding to clients. However,
   in some cases that confused clients that did not have MAC address or
   client-id; see RFC 6842. for details. That behavior has changed with the
   publication of RFC 6842. which updated RFC 2131. That update now states
   that the server must send client-id if the client sent it. That is the
   default behaviour that Kea offers. However, in some cases older devices
   that do not support RFC 6842. may refuse to accept responses that include
   the client-id option. To enable backward compatibility, an optional
   configuration parameter has been introduced. To configure it, use the
   following configuration statement:

 "Dhcp4": {
     "echo-client-id": false,
     ...
 }

  7.2.18. Using Client Identifier and Hardware Address

   DHCP server must be able to identify the client (distinguish it from other
   clients) from which it receives the message. There are many reasons why
   this identification is required and the most important ones are listed
   below.

     * When the client contacts the server to allocate a new lease, the
       server must store the client identification information in the lease
       database as a search key.
     * When the client is trying to renew or release the existing lease, the
       server must be able to find the existing lease entry in the database
       for this client, using the client identification information as a
       search key.
     * Some configurations use static reservations for the IP addresses and
       other configuration information. The server's administrator uses
       client identification information to create these static assignments.
     * In the dual stack networks there is often a need to correlate the
       lease information stored in DHCPv4 and DHCPv6 server for a particular
       host. Using common identification information by the DHCPv4 and DHCPv6
       client allows the network administrator to achieve this correlation
       and better administer the network.

   DHCPv4 makes use of two distinct identifiers which are placed by the
   client in the queries sent to the server and copied by the server to its
   responses to the client: 'chaddr' and 'client identifier'. The former was
   introduced as a part of the BOOTP specification and it is also used by
   DHCP to carry the hardware address of the interface used to send the query
   to the server (MAC address for the Ethernet). The latter is carried in the
   Client-identifier option, introduced in the RFC 2132.

   The RFC 2131 indicates that the server may use both of these identifiers
   to identify the client but the 'client identifier', if present, takes
   precedence over 'chaddr'. One of the reasons for this is that 'client
   identifier' is independent from the hardware used by the client to
   communicate with the server. For example, if the client obtained the lease
   using one network card and then the network card is moved to another host,
   the server will wrongly identify this host is the one which has obtained
   the lease. Moreover, the RFC 4361 gives the recommendation to use DUID
   (see DHCPv6 specification) carried as 'client identifier' when dual stack
   networks are in use, to provide consistent identification information of
   the client, regardless of the protocol type it is using. Kea adheres to
   these specifications and the 'client identifier' by default takes
   precedence over the value carried in 'chaddr' field when the server
   searches, creates, updates or removes the client's lease.

   When the server receives a DHCPDISCOVER or DHCPREQUEST message from the
   client, it will try to find out if the client already has a lease in the
   database and will hand out the existing lease rather than allocate a new
   one. Each lease in the lease database is associated with the 'client
   identifier' and/or 'chaddr'. The server will first use the 'client
   identifier' (if present) to search the lease. If the lease is found, the
   server will treat this lease as belonging to the client even if the
   current 'chaddr' and the 'chaddr' associated with the lease do not match.
   This facilitates the scenario when the network card on the client system
   has been replaced and thus the new MAC address appears in the messages
   sent by the DHCP client. If the server fails to find the lease using the
   'client identifier' it will perform another lookup using the 'chaddr'. If
   this lookup returns no result, the client is considered as not having a
   lease and the new lease will be created.

   A common problem reported by network operators is that bogus client
   implementations do not use stable client identifiers such as generating a
   new 'client identifier' each time the client connects to the network.
   Another well known case is when the client changes its 'client identifier'
   during the multi-stage boot process (PXE). In such cases, the MAC address
   of the client's interface remains stable and using 'chaddr' field to
   identify the client guarantees that the particular system is considered to
   be the same client, even though its 'client identifier' changes.

   To address this problem, Kea includes a configuration option which enables
   client identification using 'chaddr' only by instructing the server to
   disregard server to "ignore" the 'client identifier' during lease lookups
   and allocations for a particular subnet. Consider the following simplified
   server configuration:

 "Dhcp4": {
     ...
     "match-client-id": true,
     ...
     "subnet4": [
     {
         "subnet": "192.0.10.0/24",
         "pools": [ { "pool": "192.0.2.23-192.0.2.87" } ],
         "match-client-id": false
     },
     {
         "subnet": "10.0.0.0/8",
         "pools": [ { "pool": "10.0.0.23-10.0.2.99" } ],
     }
     ]
 }

   The match-client-id is a boolean value which controls this behavior. The
   default value of true indicates that the server will use the 'client
   identifier' for lease lookups and 'chaddr' if the first lookup returns no
   results. The false means that the server will only use the 'chaddr' to
   search for client's lease. Whether the DHCID for DNS updates is generated
   from the 'client identifier' or 'chaddr' is controlled through the same
   parameter accordingly.

   The match-client-id parameter may appear both in the global configuration
   scope and/or under any subnet declaration. In the example shown above, the
   effective value of the match-client-id will be false for the subnet
   192.0.10.0/24, because the subnet specific setting of the parameter
   overrides the global value of the parameter. The effective value of the
   match-client-id for the subnet 10.0.0.0/8 will be set to true because the
   subnet declaration lacks this parameter and the global setting is by
   default used for this subnet. In fact, the global entry for this parameter
   could be omitted in this case, because true is the default value.

   It is important to explain what happens when the client obtains its lease
   for one setting of the match-client-id and then renews when the setting
   has been changed. Let's first consider the case when the client obtains
   the lease when the match-client-id is set to true. The server will store
   the lease information including 'client identifier' (if supplied) and
   'chaddr' in the lease database. When the setting is changed and the client
   renews the lease the server will determine that it should use the 'chaddr'
   to search for the existing lease. If the client hasn't changed its MAC
   address the server should successfully find the existing lease. The
   'client identifier' associated with the returned lease is ignored and the
   client is allowed to use this lease. When the lease is renewed only the
   'chaddr' is recorded for this lease according to the new server setting.

   In the second case the client has the lease with only a 'chaddr' value
   recorded. When the setting is changed to match-client-id set to true the
   server will first try to use the 'client identifier' to find the existing
   client's lease. This will return no results because the 'client
   identifier' was not recorded for this lease. The server will then use the
   'chaddr' and the lease will be found. If the lease appears to have no
   'client identifier' recorded, the server will assume that this lease
   belongs to the client and that it was created with the previous setting of
   the match-client-id. However, if the lease contains 'client identifier'
   which is different from the 'client identifier' used by the client the
   lease will be assumed to belong to another client and the new lease will
   be allocated.

7.3. Host reservation in DHCPv4

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve specific, static
   address for exclusive use by a given client (host) - returning client will
   receive the same address from the server every time, and other clients
   will generally not receive that address. Note that there may be cases when
   the new reservation has been made for the client for the address being
   currently in use by another client. We call this situation a "conflict".
   The conflicts get resolved automatically over time as described in the
   subsequent sections. Once conflict is resolved, the client will keep
   receiving the reserved configuration when it renews.

   Another example when the host reservations are applicable is when a host
   that has specific requirements, e.g. a printer that needs additional DHCP
   options. Yet another possible use case is to define unique names for
   hosts. Although not all of the presented use cases are implemented yet,
   Kea software will support them in the near future.

   Hosts reservations are defined as parameters for each subnet. Each host
   has to be identified by its hardware/MAC address. There is an optional
   reservations array in the Subnet4 element. Each element in that array is a
   structure, that holds information about reservations for a single host. In
   particular, such a structure has to have an identifier that uniquely
   identifies a host. In DHCPv4 context, such an identifier is a hardware or
   MAC address. In most cases, also an address will be specified. It is
   possible to specify a hostname. Additional capabilities are planned.

  Note

   In Kea 1.0.0 it is only possible to create host reservations using
   client's hardware address. Host reservations by client identifier (or
   DUID) are not supported in this version of Kea. This capability will be
   implemented in Kea 1.1.0. Currently, the configuration parsing code will
   accept the "duid" parameter in the reservation configuration, but the
   server will misinterpret its value. Therefore, this parameter MUST NOT be
   used until the client identifier based host reservations are properly
   implemented and documented.

   The following example shows how to reserve addresses for specific hosts:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24",
         "interface": "eth0",
         "reservations": [
             {
                 "hw-address": "1a:1b:1c:1d:1e:1f",
                 "ip-address": "192.0.2.202"
             },
             {
                 "hw-address": "0a:0b:0c:0d:0e:0f",
                 "ip-address": "192.0.2.100",
                 "hostname": "alice-laptop"
             }
         ]
     }
 ]

   The first entry reserves the 192.0.2.202 address for the client that uses
   MAC address of 1a:1b:1c:1d:1e:1f. The second entry reserves the address
   192.0.2.100 and the hostname of alice-laptop for client using MAC address
   0a:0b:0c:0d:0e:0f. Note that if you plan to do DNS updates, it is strongly
   recommended for the hostnames to be unique.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. It is a valid configuration, if such
   definitions are specified in different subnets, though.

   Adding host reservation incurs a performance penalty. In principle, when
   the server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation, has to perform additional checks: not only if the address is
   currently used (if there is a lease for it), but also whether the address
   could be used by someone else (if there is a reservation for it). That
   additional check incurs performance penalty.

  7.3.1. Address reservation types

   In a typical scenario there is an IPv4 subnet defined, e.g. 192.0.2.0/24,
   with certain part of it dedicated for dynamic allocation by the DHCPv4
   server. That dynamic part is referred to as a dynamic pool or simply a
   pool. In principle, the host reservation can reserve any address that
   belongs to the subnet. The reservations that specify addresses that belong
   to configured pools are called in-pool reservations. In contrast, those
   that do not belong to dynamic pools are called out-of-pool reservations.
   There is no formal difference in the reservation syntax. As of 0.9.1, both
   reservation types are handled uniformly. However, upcoming releases may
   offer improved performance if there are only out-of-pool reservations as
   the server will be able to skip reservation checks when dealing with
   existing leases. Therefore, system administrators are encouraged to use
   out-of-pool reservations, if possible.

  7.3.2. Conflicts in DHCPv4 reservations

   As the reservations and lease information are stored separately, conflicts
   may arise. Consider the following series of events. The server has
   configured the dynamic pool of addresses from the range of 192.0.2.10 to
   192.0.2.20. The Host A requests an address and gets 19.0.2.10. Now the
   system administrator decides to reserve the address for the Host B. He
   decides to reserve 192.0.2.10 for that purpose. In general, reserving an
   address that is currently assigned to someone else is not recommended, but
   there are valid use cases where such an operation is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If the Host B boots up and requests an address, the server is not
   able to assign the reserved address 192.0.2.10 for the Host B. A naive
   approach would to be immediately remove the existing lease for the Host A
   and create a new one for the Host B. That would not solve the problem,
   though, because as soon as the Host B gets the address, it will detect
   that the address is already in use by the Host A and would send the
   DHCPDECLINE message. Therefore, in this situation, the server has to
   temporarily assign a different address (not matching what has been
   reserved) to the Host B.

   When the Host A renews its address, the server will discover that the
   address being renewed is now reserved for another host - the Host B.
   Therefore the server will inform the Host A that it is no longer allowed
   to use it by sending DHCPNAK message. The server will not remove the
   lease, though, as there's small chance that the DHCPNAK may be lost if the
   network is lossy. If that happens, the client will not receive any
   responses, so it will retransmit its DHCPREQUEST packet. Once the DHCPNAK
   is received by the Host A, it will then revert to the server discovery and
   will eventually get a different address. Besides allocating a new lease,
   the server will also remove the old one. As a result, the address
   192.0.2.10 will be no longer used. When Host B tries to renew its
   temporarily assigned address, the server will detect that it has a valid
   lease, but there is a reservation for a different address. The server will
   send DHCPNAK to inform Host B that its address is no longer usable, but
   will keep its lease (again, the DHCPNAK may be lost, so the server will
   keep it, until the client returns for a new address). The Host B will
   revert to the server discovery phase and will eventually send a
   DHCPREQUEST message. This time the server will find out that there is a
   reservation for that host and the reserved address 192.0.2.10 is not used,
   so it will be granted. It will also remove the lease for the temporarily
   assigned address that the Host B previously obtained.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had the Host C requested address 192.0.2.10 after the
   reservation was made, the server will either offer a different address
   (when responding to DHCPDISCOVER) or would send DHCPNAK (when responding
   to DHCPREQUEST).

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with the existing leases. This procedure takes
   time and will roughly take as long as renew-timer value specified. The
   best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address (note that
   having multiple reservations for the same address is not allowed).

  7.3.3. Reserving a hostname

   When the reservation for the client includes the hostname , the server
   will assign this hostname to the client and send it back in the Client
   FQDN or Hostname option, depending on which of them the client has sent to
   the server. The reserved hostname always takes precedence over the
   hostname supplied by the client or the autogenerated (from the IPv4
   address) hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop"
                }
             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
             "qualifying-suffix": "example.isc.org."
         }
     }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the MAC address "aa:bb:cc:dd:ee:ff". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop.isc.org."
                },
                {
                  "hw-address": "12:34:56:78:99:AA",
                  "hostname": "mark-desktop.example.org."
                }

             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
         }
     }

  7.3.4. Reserving specific options

   Currently it is not possible to specify options in host reservation. Such
   a feature will be added in the upcoming Kea releases.

  7.3.5. Fine Tuning IPv4 Host Reservation

  Note

   reservation-mode configuration parameter in DHCPv4 server is accepted, but
   not used in the Kea 0.9.1 beta. Full implementation will be available in
   the upcoming releases.

   Host reservation capability introduces additional restrictions for the
   allocation engine during lease selection and renewal. In particular, three
   major checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to be not used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address, the server has to check whether there's a reservation for this
   host, so the existing (dynamically allocated) address should be revoked
   and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments. Not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     * all - enables all host reservation types. This is the default value.
       This setting is the safest and the most flexible. It allows in-pool
       and out-of-pool reservations. As all checks are conducted, it is also
       the slowest.
     * out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting. Kea 0.9.1 does not sanity check the reservations against
       reservation-mode. Misconfiguration may cause problems.
     * disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   An example configuration that disables reservation looks like follows:

 "Dhcp4": {
     "subnet4": [
     {
         "subnet": "192.0.2.0/24",
         "reservation-mode": "disabled",
         ...
     }
     ]
 }

7.4. Server Identifier in DHCPv4

   The DHCPv4 protocol uses a "server identifier" to allow clients to
   discriminate between several servers present on the same link: this value
   is an IPv4 address of the server. The server chooses the IPv4 address of
   the interface on which the message from the client (or relay) has been
   received. A single server instance will use multiple server identifiers if
   it is receiving queries on multiple interfaces.

   Currently there is no mechanism to override the default server identifiers
   by an administrator. In the future, the configuration mechanism will be
   used to specify the custom server identifier.

7.5. How the DHCPv4 Server Selects a Subnet for the Client

   The DHCPv4 server differentiates between the directly connected clients,
   clients trying to renew leases and clients sending their messages through
   relays. For the directly connected clients the server will check the
   configuration for the interface on which the message has been received,
   and if the server configuration doesn't match any configured subnet the
   message is discarded.

   Assuming that the server's interface is configured with the IPv4 address
   192.0.2.3, the server will only process messages received through this
   interface from a directly connected client if there is a subnet configured
   to which this IPv4 address belongs, e.g. 192.0.2.0/24. The server will use
   this subnet to assign IPv4 address for the client.

   The rule above does not apply when the client unicasts its message, i.e.
   is trying to renew its lease. Such a message is accepted through any
   interface. The renewing client sets ciaddr to the currently used IPv4
   address. The server uses this address to select the subnet for the client
   (in particular, to extend the lease using this address).

   If the message is relayed it is accepted through any interface. The giaddr
   set by the relay agent is used to select the subnet for the client.

   It is also possible to specify a relay IPv4 address for a given subnet. It
   can be used to match incoming packets into a subnet in uncommon
   configurations, e.g. shared subnets. See Section 7.5.1, "Using a Specific
   Relay Agent for a Subnet" for details.

  Note

   The subnet selection mechanism described in this section is based on the
   assumption that client classification is not used. The classification
   mechanism alters the way in which a subnet is selected for the client,
   depending on the classes to which the client belongs.

  7.5.1. Using a Specific Relay Agent for a Subnet

   The relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has an IPv4 address
   configured on that interface that belongs to the subnet from which the
   server will assign addresses. In the typical case, the server is able to
   use the IPv4 address inserted by the relay (in the giaddr field of the
   DHCPv4 packet) to select the appropriate subnet.

   However, that is not always the case. In certain uncommon -- valid --
   deployments, the relay address may not match the subnet. This usually
   means that there is more than one subnet allocated for a given link. The
   two most common examples where this is the case are long lasting network
   renumbering (where both old and new address space is still being used) and
   a cable network. In a cable network both cable modems and the devices
   behind them are physically connected to the same link, yet they use
   distinct addressing. In such a case, the DHCPv4 server needs additional
   information (the IPv4 address of the relay) to properly select an
   appropriate subnet.

   The following example assumes that there is a subnet 192.0.2.0/24 that is
   accessible via a relay that uses 10.0.0.1 as its IPv4 address. The server
   will be able to select this subnet for any incoming packets that came from
   a relay that has an address in 192.0.2.0/24 subnet. It will also select
   that subnet for a relay with address 10.0.0.1.

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-address": "10.0.0.1"
             },
             ...
         }
     ],
     ...
 }

  7.5.2. Segregating IPv4 Clients in a Cable Network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 7.5.1, "Using a Specific Relay Agent for a Subnet"
   with client classification, explained in Chapter 12, Client
   Classification. One specific example is cable network, where typically
   modems get addresses from a different subnet than all devices connected
   behind them.

   Let's assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 10.1.1.0/24 subnet, while everything
   connected behind modems should get addresses from another subnet
   (192.0.2.0/24). The CMTS that acts as a relay uses address 10.1.1.1. The
   following configuration can serve that configuration:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "10.1.1.0/24",
             "pools":  [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
             "client-class" "docsis3.0",
             "relay": {
                 "ip-address": "10.1.1.1"
             }
         },
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-address": "10.1.1.1"
             }
         }
     ],
     ...
 }

7.6. Duplicate Addresses (DHCPDECLINE support)

   The DHCPv4 server is configured with a certain pool of addresses that it
   is expected to hand out to the DHCPv4 clients. It is assumed that the
   server is authoritative and has complete jurisdiction over those
   addresses. However, due to various reasons, such as misconfiguration or a
   faulty client implementation that retains its address beyond the valid
   lifetime, there may be devices connected that use those addresses without
   the server's approval or knowledge.

   Such an unwelcome event can be detected by legitimate clients (using ARP
   or ICMP Echo Request mechanisms) and reported to the DHCPv4 server using a
   DHCPDECLINE message. The server will do a sanity check (if the client
   declining an address really was supposed to use it), and then will conduct
   a clean up operation. Any DNS entries related to that address will be
   removed, the fact will be logged and hooks will be triggered. After that
   is done, the address will be marked as declined (which indicates that it
   is used by an unknown entity and thus not available for assignment to
   anyone) and a probation time will be set on it. Unless otherwise
   configured, the probation period lasts 24 hours. After that period, the
   server will recover the lease, i.e. put it back into the available state.
   The address will be available for assignment again. It should be noted
   that if the underlying issue of a misconfigured device is not resolved,
   the duplicate address scenario will repeat. On the other hand, it provides
   an opportunity to recover from such an event automatically, without any
   sysadmin intervention.

   To configure the decline probation period to a value different than the
   default, the following syntax can be used:

   "Dhcp4": {
     "decline-probation-period": 3600,
     "subnet4": [ ... ],
     ...
 }

   The parameter is expressed in seconds, so the example above will instruct
   the server to recycle declined leases after an hour.

   There are several statistics and hook points associated with the Decline
   handling procedure. The lease4_decline hook is triggered after the
   incoming DHCPDECLINE message has been sanitized and the server is about to
   decline the lease. The declined-addresses statistic is increased after the
   hook returns (both global and subnet specific variants).

   Once the probation time elapses, the declined lease is recovered using the
   standard expired lease reclamation procedure, with several additional
   steps. In particular, both declined-addresses statistics (global and
   subnet specific) are decreased. At the same time,
   reclaimed-declined-addresses statistics (again in two variants, global and
   subnet specific) are increased.

   Note about statistics: The server does not decrease assigned-addresses
   statistics when a DHCPDECLINE is received and processed successfully.
   While technically a declined address is no longer assigned, the primary
   usage of the assigned-addresses statistic is to monitor pool utilization.
   Most people would forget to include declined-addresses in the calculation,
   and simply do assigned-addresses/total-addresses. This would have a bias
   towards under-representing pool utilization. As this has a potential for
   major issues, we decided not to decrease assigned addresses immediately
   after receiving DHCPDECLINE, but to do it later when we recover the
   address back to the available pool.

7.7. Statistics in DHCPv4 server

  Note

   This section describes DHCPv4-specific statistics. For a general overview
   and usage of statistics, see Chapter 14, Statistics.

   The DHCPv4 server supports the following statistics:

   Table 7.5. DHCPv4 Statistics

 +-----------------------------------------------------------------------------+
 |               Statistic               |Data Type|Description                |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPv4 packets   |
 |                                       |         |received. This includes all|
 |             pkt4-received             | integer |packets: valid, bogus,     |
 |                                       |         |corrupted, rejected etc.   |
 |                                       |         |This statistic is expected |
 |                                       |         |to grow rapidly.           |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPDISCOVER     |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |        pkt4-discover-received         | integer |that clients that just     |
 |                                       |         |booted started their       |
 |                                       |         |configuration process and  |
 |                                       |         |their initial packets      |
 |                                       |         |reached your server.       |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPOFFER packets|
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPOFFER    |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |          pkt4-offer-received          | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPOFFER messages towards |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPREQUEST      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |         pkt4-request-received         | integer |that clients that just     |
 |                                       |         |booted received server's   |
 |                                       |         |response (DHCPOFFER),      |
 |                                       |         |accepted it and now        |
 |                                       |         |requesting an address      |
 |                                       |         |(DHCPREQUEST).             |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPACK packets  |
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPACK      |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |           pkt4-ack-received           | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPACK messages towards   |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPNAK packets  |
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPNAK      |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |           pkt4-nak-received           | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPNAK messages towards   |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPRELEASE      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |         pkt4-release-received         | integer |grow. Its increase means   |
 |                                       |         |that clients that had an   |
 |                                       |         |address are shutting down  |
 |                                       |         |or stop using their        |
 |                                       |         |addresses.                 |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPDECLINE      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |remain close to zero. Its  |
 |                                       |         |increase means that a      |
 |         pkt4-decline-received         | integer |client that leased an      |
 |                                       |         |address, but discovered    |
 |                                       |         |that the address is        |
 |                                       |         |currently used by an       |
 |                                       |         |unknown device in your     |
 |                                       |         |network.                   |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPINFORM       |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |         pkt4-inform-received          | integer |that there are clients that|
 |                                       |         |either do not need an      |
 |                                       |         |address or already have an |
 |                                       |         |address and are interested |
 |                                       |         |only in getting additional |
 |                                       |         |configuration parameters.  |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of packets received |
 |                                       |         |of an unknown type.        |
 |                                       |         |Non-zero value of this     |
 |                                       |         |statistic indicates that   |
 |         pkt4-unknown-received         | integer |the server received a      |
 |                                       |         |packet that it wasn't able |
 |                                       |         |to recognize: either with  |
 |                                       |         |unsupported type or        |
 |                                       |         |possibly malformed (without|
 |                                       |         |message type option).      |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPv4 packets   |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow every time|
 |                                       |         |the server transmits a     |
 |                                       |         |packet. In general, it     |
 |                                       |         |should roughly match       |
 |               pkt4-sent               | integer |pkt4-received, as most     |
 |                                       |         |incoming packets cause     |
 |                                       |         |server to respond. There   |
 |                                       |         |are exceptions (e.g.       |
 |                                       |         |DHCPRELEASE), so do not    |
 |                                       |         |worry, if it is lesser than|
 |                                       |         |pkt4-received.             |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPOFFER packets|
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow in most   |
 |                                       |         |cases after a DHCPDISCOVER |
 |                                       |         |is processed. There are    |
 |            pkt4-offer-sent            | integer |certain uncommon, but valid|
 |                                       |         |cases where incoming       |
 |                                       |         |DHCPDISCOVER is dropped,   |
 |                                       |         |but in general this        |
 |                                       |         |statistic is expected to be|
 |                                       |         |close to                   |
 |                                       |         |pkt4-discover-received.    |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPACK packets  |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow in most   |
 |                                       |         |cases after a DHCPREQUEST  |
 |                                       |         |is processed. There are    |
 |             pkt4-ack-sent             | integer |certain cases where DHCPNAK|
 |                                       |         |is sent instead. In        |
 |                                       |         |general, the sum of        |
 |                                       |         |pkt4-ack-sent and          |
 |                                       |         |pkt4-nak-sent should be    |
 |                                       |         |close to                   |
 |                                       |         |pkt4-request-received.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPNAK packets  |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow when the  |
 |                                       |         |server choses to not honor |
 |             pkt4-nak-sent             | integer |the address requested by a |
 |                                       |         |client. In general, the sum|
 |                                       |         |of pkt4-ack-sent and       |
 |                                       |         |pkt4-nak-sent should be    |
 |                                       |         |close to                   |
 |                                       |         |pkt4-request-received.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of incoming packets |
 |                                       |         |that could not be parsed.  |
 |                                       |         |Non-zero value of this     |
 |                                       |         |statistic indicates that   |
 |           pkt4-parse-failed           | integer |the server received        |
 |                                       |         |malformed or truncated     |
 |                                       |         |packet. This may indicate  |
 |                                       |         |problems in your network,  |
 |                                       |         |faulty clients or server   |
 |                                       |         |code bug.                  |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of incoming packets |
 |                                       |         |that were dropped. Exact   |
 |                                       |         |reason for dropping packets|
 |                                       |         |is logged, but the most    |
 |                                       |         |common reasons may be: an  |
 |           pkt4-receive-drop           | integer |unacceptable packet type,  |
 |                                       |         |direct responses are       |
 |                                       |         |forbidden, or the server-id|
 |                                       |         |sent by the client does not|
 |                                       |         |match the server's         |
 |                                       |         |server-id.                 |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |The total number of        |
 |                                       |         |addresses available for the|
 |                                       |         |DHCPv4 management. In other|
 |                                       |         |words, this is the sum of  |
 |                                       |         |all addresses in all       |
 |                                       |         |configured pools. This     |
 |                                       |         |statistic changes only     |
 |                                       |         |during configuration       |
 |                                       |         |changes. Note it does not  |
 |      subnet[id].total-addresses       | integer |take into account any      |
 |                                       |         |addresses that may be      |
 |                                       |         |reserved due to host       |
 |                                       |         |reservation. The id is the |
 |                                       |         |subnet-id of a given       |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately. This statistic |
 |                                       |         |is reset during            |
 |                                       |         |reconfiguration event.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of assigned         |
 |                                       |         |addresses in a given       |
 |                                       |         |subnet. This statistic     |
 |                                       |         |increases every time a new |
 |                                       |         |lease is allocated (as a   |
 |                                       |         |result of receiving a      |
 |                                       |         |DHCPREQUEST message) and is|
 |                                       |         |decreased every time a     |
 |     subnet[id].assigned-addresses     | integer |lease is released (a       |
 |                                       |         |DHCPRELEASE message is     |
 |                                       |         |received) or expires. The  |
 |                                       |         |id is the subnet-id of a   |
 |                                       |         |given subnet. This         |
 |                                       |         |statistic is exposed for   |
 |                                       |         |each subnet separately.    |
 |                                       |         |This statistic is reset    |
 |                                       |         |during reconfiguration     |
 |                                       |         |event.                     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that are currently         |
 |                                       |         |declined. This statistic   |
 |                                       |         |counts the number of leases|
 |                                       |         |currently unavailable. Once|
 |                                       |         |a lease is recovered, this |
 |                                       |         |statistic will be          |
 |                                       |         |decreased. Ideally, this   |
 |          declined-addresses           | integer |statistic should be zero.  |
 |                                       |         |If this statistic is       |
 |                                       |         |non-zero (or worse         |
 |                                       |         |increasing), a network     |
 |                                       |         |administrator should       |
 |                                       |         |investigate if there is a  |
 |                                       |         |misbehaving device in his  |
 |                                       |         |network. This is a global  |
 |                                       |         |statistic that covers all  |
 |                                       |         |subnets.                   |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that are currently declined|
 |                                       |         |in a given subnet. This    |
 |                                       |         |statistic counts the number|
 |                                       |         |of leases currently        |
 |                                       |         |unavailable. Once a lease  |
 |                                       |         |is recovered, this         |
 |                                       |         |statistic will be          |
 |                                       |         |decreased. Ideally, this   |
 |     subnet[id].declined-addresses     | integer |statistic should be zero.  |
 |                                       |         |If this statistic is       |
 |                                       |         |non-zero (or worse         |
 |                                       |         |increasing), a network     |
 |                                       |         |administrator should       |
 |                                       |         |investigate if there is a  |
 |                                       |         |misbehaving device in his  |
 |                                       |         |network. The id is the     |
 |                                       |         |subnet-id of a given       |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately.                |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that were declined, but    |
 |                                       |         |have now been recovered.   |
 |                                       |         |Unlike declined-addresses, |
 |                                       |         |this statistic never       |
 |     reclaimed-declined-addresses      | integer |decreases. It can be used  |
 |                                       |         |as a long term indicator of|
 |                                       |         |how many actual valid      |
 |                                       |         |Declines were processed and|
 |                                       |         |recovered from. This is a  |
 |                                       |         |global statistic that      |
 |                                       |         |covers all subnets.        |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that were declined, but    |
 |                                       |         |have now been recovered.   |
 |                                       |         |Unlike declined-addresses, |
 |                                       |         |this statistic never       |
 |                                       |         |decreases. It can be used  |
 |subnet[id].reclaimed-declined-addresses| integer |as a long term indicator of|
 |                                       |         |how many actual valid      |
 |                                       |         |Declines were processed and|
 |                                       |         |recovered from. The id is  |
 |                                       |         |the subnet-id of a given   |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately.                |
 +-----------------------------------------------------------------------------+

7.8. Management API for the DHCPv4 server

   Management API has been introduced in Kea 0.9.2-beta. It allows issuing
   specific management commands, like statistics retrieval, reconfiguration
   or shutdown. For more details, see Chapter 15, Management API. Currently
   the only supported communication channel type is UNIX stream socket. By
   default there are no sockets open. To instruct Kea to open a socket, the
   following entry in the configuration file can be used:

 "Dhcp4": {
     "control-socket": {
         "socket-type": "unix",
         "socket-name": "/path/to/the/unix/socket"
     },

     "subnet4": [
         ...
     ],
     ...
 }

   The length of the path specified by the socket-name parameter is
   restricted by the maximum length for the unix socket name on your
   operating system, i.e. the size of the sun_path field in the sockaddr_un
   structure, decreased by 1. This value varies on different operating
   systems between 91 and 107 characters. The typical values are 107 on Linux
   and 103 on FreeBSD.

   Communication over control channel is conducted using JSON structures. See
   the Control Channel section in the Kea Developer's Guide for more details.

   DHCPv4 server supports statistic-get, statistic-reset, statistic-remove,
   statistic-get-all, statistic-reset-all and statistic-remove-all, specified
   in Section 14.3, "Commands for Manipulating Statistics". It also supports
   list-commands and shutdown, specified in Section 15.3.2, "list-commands
   command" and Section 15.3.3, "shutdown command", respectively.

7.9. Supported DHCP Standards

   The following standards are currently supported:

     * Dynamic Host Configuration Protocol, RFC 2131: Supported messages are
       DHCPDISCOVER (1), DHCPOFFER (2), DHCPREQUEST (3), DHCPRELEASE (7),
       DHCPINFORM (8), DHCPACK (5), and DHCPNAK(6).
     * DHCP Options and BOOTP Vendor Extensions, RFC 2132: Supported options
       are: PAD (0), END(255), Message Type(53), DHCP Server Identifier (54),
       Domain Name (15), DNS Servers (6), IP Address Lease Time (51), Subnet
       mask (1), and Routers (3).
     * DHCP Relay Agent Information Option, RFC 3046: Relay Agent Information
       option is supported.
     * Vendor-Identifying Vendor Options for Dynamic Host Configuration
       Protocol version 4, RFC 3925: Vendor-Identifying Vendor Class and
       Vendor-Identifying Vendor-Specific Information options are supported.
     * Client Identifier Option in DHCP Server Replies, RFC 6842: Server by
       default sends back client-id option. That capability may be disabled.
       See Section 7.2.17, "Echoing Client-ID (RFC 6842)" for details.

7.10. DHCPv4 Server Limitations

   These are the current limitations of the DHCPv4 server software. Most of
   them are reflections of the current stage of development and should be
   treated as "not implemented yet", rather than actual limitations. However,
   some of them are implications of the design choices made. Those are
   clearly marked as such.

     * Removal of a subnet during server reconfiguration may cause
       renumbering of auto-generated subnet identifiers, as described in
       section Section 7.2.6, "IPv4 Subnet Identifier".
     * Host reservation (static addresses) is not supported yet.
     * Full featured client classification is not supported yet.
     * BOOTP (RFC 951) is not supported. This is a design choice. BOOTP
       support is not planned.
     * On Linux and BSD system families the DHCP messages are sent and
       received over the raw sockets (using LPF and BPF) and all packet
       headers (including data link layer, IP and UDP headers) are created
       and parsed by Kea, rather than the system kernel. Currently, Kea can
       only parse the data link layer headers with a format adhering to IEEE
       802.3 standard and assumes this data link layer header format for all
       interfaces. Hence, Kea will fail to work on interfaces which use
       different data link layer header formats (e.g. Infiniband).
     * The DHCPv4 server does not verify that assigned address is unused.
       According to RFC 2131, the allocating server should verify that
       address is not used by sending ICMP echo request.
     * Address duplication report (DECLINE) is not supported yet.

                          Chapter 8. The DHCPv6 Server

   Table of Contents

   8.1. Starting and Stopping the DHCPv6 Server

   8.2. DHCPv6 Server Configuration

                8.2.1. Introduction

                8.2.2. Lease Storage

                8.2.3. Interface selection

                8.2.4. IPv6 Subnet Identifier

                8.2.5. Unicast traffic support

                8.2.6. Subnet and Address Pool

                8.2.7. Subnet and Prefix Delegation Pools

                8.2.8. Standard DHCPv6 options

                8.2.9. Custom DHCPv6 options

                8.2.10. DHCPv6 vendor specific options

                8.2.11. Nested DHCPv6 options (custom option spaces)

                8.2.12. Unspecified parameters for DHCPv6 option
                configuration

                8.2.13. IPv6 Subnet Selection

                8.2.14. Rapid Commit

                8.2.15. DHCPv6 Relays

                8.2.16. Relay-Supplied Options

                8.2.17. Client Classification in DHCPv6

                8.2.18. Configuring DHCPv6 for DDNS

   8.3. Host reservation in DHCPv6

                8.3.1. Address/prefix reservation types

                8.3.2. Conflicts in DHCPv6 reservations

                8.3.3. Reserving a hostname

                8.3.4. Reserving specific options

                8.3.5. Fine Tuning IPv6 Host Reservation

   8.4. Server Identifier in DHCPv6

   8.5. Stateless DHCPv6 (Information-Request Message)

   8.6. Support for RFC 7550

   8.7. Using specific relay agent for a subnet

   8.8. Segregating IPv6 clients in a cable network

   8.9. MAC/Hardware addresses in DHCPv6

   8.10. Duplicate Addresses (DECLINE support)

   8.11. Statistics in DHCPv6 server

   8.12. Management API for the DHCPv6 server

   8.13. Supported DHCPv6 Standards

   8.14. DHCPv6 Server Limitations

8.1. Starting and Stopping the DHCPv6 Server

   It is recommended that the Kea DHCPv6 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       verbose mode. In verbose mode, the logging severity and debuglevel
       specified in the configuration file are ignored and "debug" severity
       and the maximum debuglevel (99) are assumed. The flag is convenient,
       for temporarily switching the server into maximum verbosity, e.g. when
       debugging.
     * -p port - specifies UDP port on which the server will listen. This is
       only useful during testing, as a DHCPv6 server listening on ports
       other than default DHCPv6 ports will not be able to handle regular
       DHCPv6 queries.
     * -v - prints out Kea version and exits.
     * -V - prints out Kea extended version with additional parameters and
       exits.
     * -W - prints out Kea configuration report and exits.

   The -V command returns the versions of the external libraries dynamically
   linked.

   The -W command describes the environment used to build Kea. This command
   displays a copy of the config.report file produced by ./configure that is
   embedded in the executable binary.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/dhcp6/.libs/kea-dhcp6.

 strings path/kea-dhcp6 | sed -n 's/;;;; //p'

   When running in a console, the server can be shut down by pressing ctrl-c.
   It detects the key combination and shuts down gracefully.

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file.

   Since the DHCPv6 server opens privileged ports, it requires root access.
   Make sure you run this daemon as root.

   During startup the server will attempt to create a PID file of the form:
   [localstatedir]/[conf name].kea-dhcp6.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP6_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

8.2. DHCPv6 Server Configuration

  8.2.1. Introduction

   This section explains how to configure the DHCPv6 server using the Kea
   configuration backend. (Kea configuration using any other backends is
   outside of scope of this document.) Before DHCPv6 is started, its
   configuration file has to be created. The basic configuration looks as
   follows:

 {
 # DHCPv6 configuration starts on the next line
 "Dhcp6": {

 # First we set up global values
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "preferred-lifetime": 3000,
     "valid-lifetime": 4000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of a lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp6.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ]
         }
     ]
 # DHCPv6 configuration ends with the next line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example and their format. Subsequent sections of this chapter go
   into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration consists of one or more objects. In
   this specific example, we have only one object called Dhcp6. This is a
   simplified configuration, as usually there will be additional objects,
   like Logging or DhcpDns, but we omit them now for clarity. The Dhcp6
   configuration starts with the "Dhcp6": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp6 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may require moving the comma as well. The second caveat is
   that it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv6 configuration elements, the very first few elements
   define some global parameters. valid-lifetime defines for how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   The address will become deprecated in 3000 seconds (clients are allowed to
   keep old connections, but can't use this address for creating new
   connections). renew-timer and rebind-timer are values that define T1 and
   T2 timers that govern when the client will begin the renewal and rebind
   procedures.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually, lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example -- type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters follow, a
   trailing comma is present.

   Finally, we need to define a list of IPv6 subnets. This is the most
   important DHCPv6 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet6 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pool (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet6 parameter would be specified and
   separated by commas. For example, to define two subnets, the following
   syntax would be used:

 "subnet6": [
     {
         "pools": [
         {
             "pool": "2001:db8:1::/112"
         }
         ],
         "subnet": "2001:db8:1::/64"
     },
     {
         "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
         "subnet": "2001:db8:2::/64",
         "interface": "eth0"
     }
 ]

   Note that indentation is optional and is used for aesthetic purposes only.
   In some cases in may be preferable to use more compact notation.

   After all parameters are specified, we have two contexts open: global and
   Dhcp6, hence we need two closing curly brackets to close them. In a real
   life configuration file there most likely would be additional components
   defined such as Logging or DhcpDdns, so the closing brace would be
   followed by a comma and another object definition.

  8.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are three database backends available: memfile (which is
   the default backend), MySQL and PostgreSQL.

    8.2.2.1. Memfile, Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 8.2.2.2,
   "Lease Database Configuration" describes this option. In typical smaller
   deployments though, the server will use a CSV file rather than a database
   to store lease information. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp6/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list presents the remaining, not mandatory parameters, which can
   be used to configure the Memfile backend.

     * persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     * name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases6.csv" .
     * lfc-interval: specifies the interval in seconds, at which the server
       (Memfile backend) will perform a lease file cleanup (LFC), which
       removes the redundant (historical) information from the lease file and
       effectively reduces the lease file size. The cleanup process is
       described in more detailed fashion further in this section. The
       default value of the lfc-interval is 0, which disables the LFC.

   The example configuration of the Memfile backend is presented below:

 "Dhcp6": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases6.csv",
         "lfc-interval": 1800
     }
 }

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time when
   the server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not supersede the existing client's lease, as it
   would require the lookup of the specific lease entry, but simply appends
   the new lease information at the end of the lease file. The previous lease
   entries for the client are not removed. When the server loads leases from
   the lease file, e.g. at the server startup, it assumes that the latest
   lease entry for the client is the valid one. The previous entries are
   discarded. This means that the server can re-construct the accurate
   information about the leases even though there may be many lease entries
   for each client. However, storing many entries for each client results in
   bloated lease file and impairs the performance of the server's startup and
   reconfiguration, as it needs to process larger number of lease entries.

   The lease file cleanup removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   renewals are, the lesser value of the lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But, this implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server, which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for completing
   the cleanup before the new cleanup is triggered.

   The LFC is performed by a separate process (in background) to avoid
   performance impact on the server process. In order to avoid the conflicts
   between the two processes both using the same lease files, the LFC process
   operates on the copy of the original lease file, rather than on the lease
   file used by the server to record lease updates. There are also other
   files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located on the Kea wiki:
   http://kea.isc.org/wiki/LFCDesign.

    8.2.2.2. Lease Database Configuration

  Note

   Lease database access information must be configured for the DHCPv6
   server, even if it has already been configured for the DHCPv4 server. The
   servers store their information independently, so each server can use a
   separate database or both servers can use the same database.

   Lease database configuration is controlled through the
   Dhcp6/lease-database parameters. The type of the database must be set to
   "memfile", "mysql" or "postgresql", e.g.

 "Dhcp6": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database is to hold the leases must be set: this is
   the name used when the lease database was created (see Section 4.3.2.1,
   "First Time Creation of Kea Database" or Section 4.3.3.1, "Manually Create
   the PostgreSQL Database and the Kea User").

 "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system than the DHCPv6 server,
   the database host name must also be specified (although it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp6": { "lease-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv6 server. In this case, set the value to the empty
   string:

 "Dhcp6": { "lease-database": { "host" : "", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp6": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

  8.2.3. Interface selection

   The DHCPv6 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration instructs the
   server to listen on all available interfaces:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 }

   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   the actual interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this will form of usage only be used where it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

  8.2.4. IPv6 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with
   respective subnets. When the subnet identifier is not specified for a
   subnet being configured, it will be automatically assigned by the
   configuration mechanism. The identifiers are assigned from 1 and are
   monotonically increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, which may have unexpected consequences.
   In the future it is planned to implement a mechanism to preserve
   auto-generated subnet ids upon removal of one of the subnets. Currently,
   the only remedy for this issue is to manually specify a unique subnet
   identifier for each subnet.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  8.2.5. Unicast traffic support

   When the DHCPv6 server starts, by default it listens to the DHCP traffic
   sent to multicast address ff02::1:2 on each interface that it is
   configured to listen on (see Section 8.2.3, "Interface selection"). In
   some cases it is useful to configure a server to handle incoming traffic
   sent to the global unicast addresses as well. The most common reason for
   that is to have relays send their traffic to the server directly. To
   configure the server to listen on a specific unicast address, the notation
   to specify interfaces has been extended. An interface name can be
   optionally followed by a slash, followed by the global unicast address on
   which the server should listen. This will be done in addition to normal
   link-local binding + listening on ff02::1:2 address. The sample
   configuration below shows how to listen on 2001:db8::1 (a global address)
   configured on the eth1 interface.

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1/2001:db8::1" ]
     },
     ...
 }


   This configuration will cause the server to listen on eth1 on link-local
   address, multicast group (ff02::1:2) and 2001:db8::1.

   It is possible to mix interface names, wildcards and interface
   name/addresses on the list of interfaces. It is not possible to specify
   more than one unicast address on a given interface.

   Care should be taken to specify proper unicast addresses. The server will
   attempt to bind to those addresses specified, without any additional
   checks. This approach is selected on purpose, so the software can be used
   to communicate over uncommon addresses if the administrator so desires.

  8.2.6. Subnet and Address Pool

   The essential role of a DHCPv6 server is address assignment. For this, the
   server has to be configured with at least one subnet and one pool of
   dynamic addresses to be managed. For example, assume that the server is
   connected to a network segment that uses the 2001:db8:1::/64 prefix. The
   Administrator of that network has decided that addresses from range
   2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
   server. Such a configuration can be achieved in the following way:

 "Dhcp6": {
     "subnet6": [
        {
            "subnet": "2001:db8:1::/64",
            "pools": [
                {
                    "pool": "2001:db8:1::1-2001:db8:1::ffff"
                }
            ],
            ...
        }
     ]
 }

   Note that subnet is defined as a simple string, but the pool parameter is
   actually a list of pools: for this reason, the pool definition is enclosed
   in square brackets, even though only one range of addresses is specified.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 2001:db8:1:0:5::/80 should also be
   managed by the server. It could be written as 2001:db8:1:0:5:: to
   2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's is cumbersome. It
   can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are
   supported by Dhcp6 and can be mixed in the pool list. For example, one
   could define the following pools:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" },
             { "pool": "2001:db8:1:05::/80" }
         ],
         ...
     }
     ]
 }

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible.

   The server may be configured to serve more than one subnet. To add a
   second subnet, use a command similar to the following:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" }
         ]
     },
     {
         "subnet": "2001:db8:2::/64",
         "pools": [
             { "pool": "2001:db8:2::/64" }
         ]
     },

         ...
     ]
 }

   In this example, we allow the server to dynamically assign all addresses
   available in the whole subnet. Although rather wasteful, it is certainly a
   valid configuration to dedicate the whole /64 subnet for that purpose.
   Note that the Kea server does not preallocate the leases, so there is no
   danger in using gigantic address pools.

   When configuring a DHCPv6 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) address from that pool. For example for pool
   2001:db8:2::/64 the 2001:db8:2:: address may be assigned as well. If you
   want to avoid this, use the "min-max" notation.

  8.2.7. Subnet and Prefix Delegation Pools

   Subnets may also be configured to delegate prefixes, as defined in RFC
   3633. A subnet may have one or more prefix delegation pools. Each pool has
   a prefixed address, which is specified as a prefix and a prefix length, as
   well as a delegated prefix length. delegated-len must not be shorter (that
   is it must be numerically greater or equal) than prefix-len. If both
   delegated-len and prefix-len are equal, the server will be able to
   delegate only one prefix. The delegated prefix does not have to match the
   subnet prefix.

   Below is a sample subnet configuration which enables prefix delegation for
   the subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:d8b:1::/64",
             "pd-pools": [
                 {
                     "prefix": "3000:1::",
                     "prefix-len": 64,
                     "delegated-len": 96
                 }
             ]
         }
     ],
     ...
 }

  8.2.8. Standard DHCPv6 options

   One of the major features of a DHCPv6 server is to provide configuration
   options to clients. Although there are several options that require
   special behavior, most options are sent by the server only if the client
   explicitly requests them. The following example shows how to configure DNS
   servers, which is one of the most frequently used options. Numbers in the
   first column are added for easier reference and will not appear on screen.
   Options specified in this way are considered global and apply to all
   configured subnets.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": true,
            "data": "2001:db8::cafe, 2001:db8::babe"
         },
         ...
     ]
 }

   The option-data> line creates a new entry in the option-data table. This
   table contains information on all global options that the server is
   supposed to configure in all subnets. The name line specifies the option
   name. (For a complete list of currently supported names, see Table 8.1,
   "List of standard DHCPv6 options".) The next line specifies the option
   code, which must match one of the values from that list. The line
   beginning with space specifies the option space, which must always be set
   to "dhcp6" as these are standard DHCPv6 options. For other name spaces,
   including custom option spaces, see Section 8.2.11, "Nested DHCPv6 options
   (custom option spaces)". The next line specifies the format in which the
   data will be entered: use of CSV (comma separated values) is recommended.
   The data line gives the actual value to be sent to clients. Data is
   specified as normal text, with values separated by commas if more than one
   value is allowed.

   Options can also be configured as hexadecimal values. If "csv-format" is
   set to false, the option data must be specified as a string of hexadecimal
   numbers. The following commands configure the DNS-SERVERS option for all
   subnets with the following addresses: 2001:db8:1::cafe and
   2001:db8:1::babe.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": false,
            "data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
                     2001 0DB8 0001 0000 0000 0000 0000 BABE"
         },
         ...
     ]
 }

   The value for the setting of the "data" element is split across two lines
   in this document for clarity: when entering the command, the whole string
   should be entered on the same line. Care should be taken to use proper
   encoding when using hexadecimal format as Kea's ability to validate data
   correctness in hexadecimal is limited.

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 8.2.12,
   "Unspecified parameters for DHCPv6 option configuration".

   It is possible to override options on a per-subnet basis. If clients
   connected to most of your subnets are expected to get the same values of a
   given option, you should use global options: you can then override
   specific values for a small number of subnets. On the other hand, if you
   use different values in each subnet, it does not make sense to specify
   global option values (Dhcp6/option-data), rather you should set only
   subnet-specific values (Dhcp6/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 2001:db8:1::3.

 "Dhcp6": {
     "subnet6": [
         {
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:1::3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   The currently supported standard DHCPv6 options are listed in Table 8.1,
   "List of standard DHCPv6 options". The "Name" and "Code" are the values
   that should be used as a name in the option-data structures. "Type"
   designates the format of the data: the meanings of the various types is
   given in Table 7.3, "List of standard DHCP option types".

   Experimental options (like standard options but with a code which was not
   assigned by IANA) are listed in Table 8.2, "List of experimental DHCPv6
   options".

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option dns-servers
   allows the specification of more than one IPv6 address, allowing clients
   to obtain the addresses of multiple DNS servers.

   The Section 8.2.9, "Custom DHCPv6 options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea does not provide a definition yet. In order to use such options, a
   server administrator must create a definition as described in
   Section 8.2.9, "Custom DHCPv6 options" in the 'dhcp6' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism would allow any option format as it has no
   means to validate the format at the moment.

   Table 8.1. List of standard DHCPv6 options

   +------------------------------------------------------------------------+
   |           Name           | Code |            Type             | Array? |
   |--------------------------+------+-----------------------------+--------|
   | preference               |  7   |            uint8            | false  |
   |--------------------------+------+-----------------------------+--------|
   | vendor-opts              |  17  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | sip-server-dns           |  21  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | sip-server-addr          |  22  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | dns-servers              |  23  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | domain-search            |  24  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nis-servers              |  27  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nisp-servers             |  28  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nis-domain-name          |  29  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nisp-domain-name         |  30  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | sntp-servers             |  31  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | information-refresh-time |  32  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | bcmcs-server-dns         |  33  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | bcmcs-server-addr        |  34  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | geoconf-civic            |  36  |   record (uint8, uint16,    | false  |
   |                          |      |           binary)           |        |
   |--------------------------+------+-----------------------------+--------|
   | remote-id                |  37  |   record (uint32, binary)   | false  |
   |--------------------------+------+-----------------------------+--------|
   | subscriber-id            |  38  |           binary            | false  |
   |--------------------------+------+-----------------------------+--------|
   | client-fqdn              |  39  |    record (uint8, fqdn)     | false  |
   |--------------------------+------+-----------------------------+--------|
   | pana-agent               |  40  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | new-posix-timezone       |  41  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | new-tzdb-timezone        |  42  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | ero                      |  43  |           uint16            |  true  |
   |--------------------------+------+-----------------------------+--------|
   | lq-query                 |  44  |       record (uint8,        | false  |
   |                          |      |        ipv6-address)        |        |
   |--------------------------+------+-----------------------------+--------|
   | client-data              |  45  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | clt-time                 |  46  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | lq-relay-data            |  47  |    record (ipv6-address,    | false  |
   |                          |      |           binary)           |        |
   |--------------------------+------+-----------------------------+--------|
   | lq-client-link           |  48  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | bootfile-url             |  59  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | bootfile-param           |  60  |           binary            | false  |
   |--------------------------+------+-----------------------------+--------|
   | client-arch-type         |  61  |           uint16            |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nii                      |  62  |    record (uint8, uint8,    | false  |
   |                          |      |           uint8)            |        |
   |--------------------------+------+-----------------------------+--------|
   | erp-local-domain-name    |  65  |            fqdn             | false  |
   |--------------------------+------+-----------------------------+--------|
   | rsoo                     |  66  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | client-linklayer-addr    |  79  |           binary            | false  |
   |--------------------------+------+-----------------------------+--------|
   | dhcp4o6-server-addr      |  88  |        ipv6-address         |  true  |
   +------------------------------------------------------------------------+

   Table 8.2. List of experimental DHCPv6 options

   +-------------------------------------------------------------+
   |    Name     | Code |             Type              | Array? |
   |-------------+------+-------------------------------+--------|
   | public-key  | 701  |            binary             | false  |
   |-------------+------+-------------------------------+--------|
   | certificate | 702  |            binary             | false  |
   |-------------+------+-------------------------------+--------|
   | signature   | 703  | record (uint8, uint8, binary) | false  |
   |-------------+------+-------------------------------+--------|
   | timestamp   | 704  |            binary             | false  |
   +-------------------------------------------------------------+

  8.2.9. Custom DHCPv6 options

   It is also possible to define options other than the standard ones. Assume
   that we want to define a new DHCPv6 option called "foo" which will have
   code 100 and will convey a single unsigned 32 bit integer value. We can
   define such an option by using the following commands:

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 100,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp6",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "false" value of the "array" parameter determines that the option does
   NOT comprise an array of "uint32" values but rather a single value. Two
   other parameters have been left blank: "record-types" and "encapsulate".
   The former specifies the comma separated list of option data fields if the
   option comprises a record of data fields. The "record-fields" value should
   be non-empty if the "type" is set to "record". Otherwise it must be left
   blank. The latter parameter specifies the name of the option space being
   encapsulated by the particular option. If the particular option does not
   encapsulate any option space it should be left blank. Note that the above
   set of comments define the format of the new option and do not set its
   values.

   The name, code and type parameters are required, all others are optional.
   The array default value is false. The record-types and encapsulate default
   values are blank (i.e. ""). The default space is "dhcp6".

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "code": 100,
             "space": "dhcp6",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv6-address etc): it is possible to define an option
   comprising a number of existing primitives.

   Assume we want to define a new option that will consist of an IPv6
   address, followed by an unsigned 16 bit integer, followed by a boolean
   value, followed by a text string. Such an option could be defined in the
   following way:

 "Dhcp6": {
     "option-def": [
         {
             "name": "bar",
             "code": 101,
             "space": "dhcp6",
             "type": "record",
             "array": false,
             "record-types": "ipv6-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "type" is set to "record" to indicate that the option contains
   multiple values of different types. These types are given as a
   comma-separated list in the "record-types" field and should be those
   listed in Table 7.3, "List of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp6": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp6",
             "code": 101,
             "csv-format": true,
             "data": "2001:db8:1::10, 123, false, Hello World"
         }
     ],
     ...
 }

   csv-format is set true to indicate that the data field comprises a
   command-separated list of values. The values in the "data" must correspond
   to the types set in the "record-types" field of the option definition.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future Kea versions will accept all those
   values for all boolean parameters.

  8.2.10. DHCPv6 vendor specific options

   Currently there are two option spaces defined for the DHCPv6 daemon:
   "dhcp6" (for top level DHCPv6 options) and "vendor-opts-space", which is
   empty by default, but options can be defined in it. Those options will be
   carried in the Vendor-specific Information option (code 17). The following
   examples show how to define an option "foo" with code 1 that consists of
   an IPv6 address, an unsigned 16 bit integer and a string. The "foo" option
   is conveyed in a Vendor-specific Information option. This option comprises
   a single uint32 value that is set to "12345". The sub-option "foo" follows
   the data field holding this value.

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-opts-space",
             "type": "record",
             "array": false,
             "record-types": "ipv6-address, uint16, string",
             "encapsulate": ""
         }
     ],
     ...
 }

   (Note that the option space is set to vendor-opts-space.) Once the option
   format is defined, the next step is to define actual values for that
   option:

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-opts-space",
             "data": "2001:db8:1::10, 123, Hello World"
         },
         ...
     ],
     ...
 }

   We should also define a value (enterprise-number) for the Vendor-specific
   Information option, that conveys our option "foo".

 "Dhcp6": {
     "option-data": [
         ...,
         {
             "name": "vendor-opts",
             "data": "12345"
         }
     ],
     ...
 }

   Alternatively, the option can be specified using its code.

 "Dhcp6": {
     "option-data": [
         ...,
         {
             "code": 17,
             "data": "12345"
         }
     ],
     ...
 }

  8.2.11. Nested DHCPv6 options (custom option spaces)

   It is sometimes useful to define completely new option spaces. This is
   useful if the user wants his new option to convey sub-options that use a
   separate numbering scheme, for example sub-options with codes 1 and 2.
   Those option codes conflict with standard DHCPv6 options, so a separate
   option space must be defined.

   Note that it is not required to create a new option space when defining
   sub-options for a standard option because it is created by default if the
   standard option is meant to convey any sub-options (see Section 8.2.10,
   "DHCPv6 vendor specific options").

   Assume that we want to have a DHCPv6 option called "container" with code
   102 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp6": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv6-address",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv6 option and specify that it
   should include options from the isc option space:

 "Dhcp6": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 102,
             "space": "dhcp6",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the encapsulate field. The type field is set to empty which limits this
   option to only carrying data in sub-options.

   Finally, we can set values for the new options:

 "Dhcp6": {
     "option-data": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "data": "2001:db8::abcd"
         },
         }
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "data": "Hello world"
         },
         {
             "name": "container",
             "code": 102,
             "space": "dhcp6"
         }
     ],
     ...
 }

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the "type" value
   would have to be set to "uint16" in the option definition. (Such an option
   would then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the "data" parameter -- which
   should be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  8.2.12. Unspecified parameters for DHCPv6 option configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values can be used. However, it is important
   to understand the implications of not specifying some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     * name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     * code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     * space - if the option space is unspecified it will default to 'dhcp6'
       which is an option space holding DHCPv6 standard options.
     * data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which spec allows
       for the length of 0. For such options, the data parameter may be
       omitted in the configuration.
     * csv-format - if this value is not specified and the definition for the
       particular option exists, the server will assume that the option data
       is specified as a list of comma separated values to be assigned to
       individual fields of the DHCP option. If the definition does not exist
       for this option, the server will assume that the data parameter
       contains the option payload in the binary format (represented as a
       string of hexadecimal digits). Note that not specifying this parameter
       doesn't imply that it defaults to a fixed value, but the configuration
       data interpretation also depends on the presence of the option
       definition. An administrator must be aware if the definition for the
       particular option exists when this parameter is not specified. It is
       generally recommended to not specify this parameter only for the
       options for which the definition exists, e.g. standard options.
       Setting csv-format to an explicit value will cause the server to
       strictly check the format of the option data specified.

  8.2.13. IPv6 Subnet Selection

   The DHCPv6 server may receive requests from local (connected to the same
   subnet as the server) and remote (connecting via relays) clients. As the
   server may have many subnet configurations defined, it must select an
   appropriate subnet for a given request.

   The server can not assume which of the configured subnets are local. In
   IPv4 it is possible as there is a reasonable expectation that the server
   will have a (global) IPv4 address configured on the interface, and can use
   that information to detect whether a subnet is local or not. That
   assumption is not true in IPv6, the DHCPv6 server must be able to operate
   while only having link-local addresses. Therefore an optional "interface"
   parameter is available within a subnet definition to designate that a
   given subnet is local, i.e. reachable directly over the specified
   interface. For example the server that is intended to serve a local subnet
   over eth0 may be configured as follows:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface": "eth0"
         }
     ],
     ...
 }

  8.2.14. Rapid Commit

   The Rapid Commit option, described in RFC 3315, is supported by the Kea
   DHCPv6 server. However, support is disabled by default for all subnets. It
   can be enabled for a particular subnet using the rapid-commit parameter as
   shown below:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "rapid-commit": true,
             "pools": [
                  {
                      "pool": "2001:db8:beef::1-2001:db8:beef::10"
                  }
              ],
         }
     ],
     ...
 }

   This setting only affects the subnet for which the rapid-commit is set to
   true. For clients connected to other subnets, the server will ignore the
   Rapid Commit option sent by the client and will follow the 4-way exchange
   procedure, i.e. respond with the Advertise for the Solicit containing
   Rapid Commit option.

  8.2.15. DHCPv6 Relays

   A DHCPv6 server with multiple subnets defined must select the appropriate
   subnet when it receives a request from a client. For clients connected via
   relays, two mechanisms are used:

   The first uses the linkaddr field in the RELAY_FORW message. The name of
   this field is somewhat misleading in that it does not contain a link-layer
   address: instead, it holds an address (typically a global address) that is
   used to identify a link. The DHCPv6 server checks if the address belongs
   to a defined subnet and, if it does, that subnet is selected for the
   client's request.

   The second mechanism is based on interface-id options. While forwarding a
   client's message, relays may insert an interface-id option into the
   message that identifies the interface on the relay that received the
   message. (Some relays allow configuration of that parameter, but it is
   sometimes hardcoded and may range from the very simple (e.g. "vlan100") to
   the very cryptic: one example seen on real hardware was
   "ISAM144|299|ipv6|nt:vp:1:110"). The server can use this information to
   select the appropriate subnet. The information is also returned to the
   relay which then knows the interface to use to transmit the response to
   the client. In order for this to work successfully, the relay interface
   IDs must be unique within the network and the server configuration must
   match those values.

   When configuring the DHCPv6 server, it should be noted that two
   similarly-named parameters can be configured for a subnet:

     * "interface" defines which local network interface can be used to
       access a given subnet.
     * "interface-id" specifies the content of the interface-id option used
       by relays to identify the interface on the relay to which the response
       packet is sent.

   The two are mutually exclusive: a subnet cannot be both reachable locally
   (direct traffic) and via relays (remote traffic). Specifying both is a
   configuration error and the DHCPv6 server will refuse such a
   configuration.

   To specify interface-id with value "vlan123", the following commands can
   be used:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface-id": "vlan123"
         }
     ],
     ...
 }

  8.2.16. Relay-Supplied Options

   RFC 6422 defines a mechanism called Relay-Supplied DHCP Options. In
   certain cases relay agents are the only entities that may have specific
   information. They can insert options when relaying messages from the
   client to the server. The server will then do certain checks and copy
   those options to the response that will be sent to the client.

   There are certain conditions that must be met for the option to be
   included. First, the server must not provide the option by itself. In
   other words, if both relay and server provide an option, the server always
   takes precedence. Second, the option must be RSOO-enabled. IANA maintains
   a list of RSOO-enabled options here. However, there may be cases when
   system administrators want to echo other options. Kea can be instructed to
   treat other options as RSOO-enabled. For example, to mark options 110, 120
   and 130 as RSOO-enabled, the following syntax should be used:

 "Dhcp6": {
     "relay-supplied-options": [ "110", "120", "130" ],
     ...
 }

   As of March 2015, only option 65 is RSOO-enabled by IANA. This option will
   always be treated as such and there's no need to explicitly mark it. Also,
   when enabling standard options, it is possible to use their names, rather
   than option code, e.g. (e.g. use dns-servers instead of 23). See
   Table 8.1, "List of standard DHCPv6 options" for the names. In certain
   cases it could also work for custom options, but due to the nature of the
   parser code this may be unreliable and should be avoided.

  8.2.17. Client Classification in DHCPv6

   The DHCPv6 server includes support for client classification. At the
   current time the capabilities of the classification process are limited
   but it is expected they will be expanded in the future. For a deeper
   discussion of the classification process see Chapter 12, Client
   Classification.

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. It is envisaged that client
   classification will be used for changing the behavior of almost any part
   of the DHCP message processing, including the assignment of leases from
   different pools, the assignment of different options (or different values
   of the same options) etc. In the current release of the software however,
   there are only two mechanisms that take advantage of client
   classification: subnet selection and assignment of different options.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario is cable
   networks. There are two classes of devices: the cable modem itself, which
   should be handed a lease from subnet A and all other devices behind the
   modem that should get a lease from subnet B. That segregation is essential
   to prevent overly curious users from playing with their cable modems. For
   details on how to set up class restrictions on subnets, see Section 12.5,
   "Configuring Subnets With Class Information".

   The process of doing classification is conducted in three steps. The first
   step is to assess an incoming packet and assign it to zero or more
   classes. The second step is to choose a subnet, possibly based on the
   class information. The third step is to assign options again possibly
   based on the class information.

   There are two methods of doing classification. The first is automatic and
   relies on examining the values in the vendor class options. Information
   from these options is extracted and a class name is constructed from it
   and added to the class list for the packet. The second allows you to
   specify an expression that is evaluated for each packet. If the result is
   true the packet is a member of the class.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

    8.2.17.1. Defining and Using Custom Classes

   The following example shows how to configure a class using an expression
   and a subnet making use of that class. This configuration defines the
   class named "Client_enterprise". It is comprised of all clients who's
   client identifiers start with the given hex string (which would indicate a
   DUID based on an enterprise id of 0xAABBCCDD). They will be given an
   address from 2001:db8:1::0 to 2001:db8:1::FFFF and 2001:db8:0::1 and
   2001:db8:2::1 for their domain name servers. For a deeper discussion of
   the classification process see Chapter 12, Client Classification.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
             "client-class": "Client_enterprise"
         }
     ],
     ...
 }

   This example shows a configuration using an automatically generated
   "VENDOR_CLASS_" class. The Administrator of the network has decided that
   addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are going to be
   managed by the Dhcp6 server and only clients belonging to the eRouter1.0
   client class are allowed to use that pool.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::-2001:db8:1::ffff"
                  }
              ],
             "client-class": "VENDOR_CLASS_eRouter1.0"
         }
     ],
     ...
 }

  8.2.18. Configuring DHCPv6 for DDNS

   As mentioned earlier, kea-dhcp6 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2") to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (AAAA records),
       reverse DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters controlling the generation of NCRs for submission to D2 are
   contained in the "dhcp-ddns" section of kea-dhcp6 configuration. The
   mandatory parameters for the DHCP DDNS configuration are enable-updates
   which is unconditionally required, and qualifying-suffix which has no
   default value and is required when enable-updates is set to true. The two
   (disabled and enabled) minimal DHCP DDNS configurations are:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     * "server-ip": "127.0.0.1"
     * "server-port": 53001
     * "sender-ip": ""
     * "sender-port": 0
     * "max-queue-size": 1024
     * "ncr-protocol": "UDP"
     * "ncr-format": "JSON"
     * "override-no-update": false
     * "override-client-update": false
     * "replace-client-name": false
     * "generated-prefix": "myhost"

    8.2.18.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp6 must be able to
   communicate with it. kea-dhcp6 uses the following configuration parameters
   to control how it communications with D2:

     * enable-updates - determines whether or not kea-dhcp6 will generate
       NCRs. If missing, this value is assumed to be false hence DDNS updates
       are disabled. To enable DDNS updates set this value to true:
     * server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * server-port - port on which D2 listens for requests. The default value
       is 53001.
     * sender-ip - IP address which kea-dhcp6 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp6 to select a
       suitable address.
     * sender-port - port which kea-dhcp6 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp6 to select a suitable port.
     * max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intent is to allow kea-dhcp6 to
       continue lease operations. The default value is 1024.
     * ncr-protocol - Socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     * ncr-format - Packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to running on the same machine as
   kea-dhcp6, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must altered accordingly. For example, if D2
   has been configured to listen on 2001:db8::5 port 900, the following
   commands would be required:

 "Dhcp6": {
     "dhcp-ddns": {
         "server-ip": "2001:db8::5",
         "server-port": 900,
         ...
     },
     ...
 }

    8.2.18.2. When does kea-dhcp6 generate DDNS request

   kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704. It
   is important to keep in mind that kea-dhcp6 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are the purview of D2 (Chapter 10, The
   DHCP-DDNS Server).

   This section describes when kea-dhcp6 will generate NCRs and the
   configuration parameters that can be used to influence this decision. It
   assumes that the "enable-updates" parameter is true.

  Note

   Currently the interface between kea-dhcp6 and D2 only supports requests
   which update DNS entries for a single IP address. If a lease grants more
   than one address, kea-dhcp6 will create the DDNS update request for only
   the first of these addresses. Support for multiple address mappings may be
   provided in a future release.

   In general, kea-dhcp6 will generate DDNS update requests when:

    1. A new lease is granted in response to a DHCP REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a DHCP RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made. The decision making
   involved when granting a new lease is more involved and is discussed next.

   kea-dhcp6 will generate a DDNS update request only if the DHCP REQUEST
   contains the FQDN option (code 39). By default kea-dhcp6 will respect the
   FQDN N and S flags specified by the client as shown in the following
   table:

   Table 8.3. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp6 will honor the
   client's wishes and generate a DDNS request to D2 to update only reverse
   DNS data. The parameter, "override-client-update", can be used to instruct
   the server to override client delegation requests. When this parameter is
   true, kea-dhcp6 will disregard requests for client delegation and generate
   a DDNS request to update both forward and reverse DNS data. In this case,
   the N-S-O flags in the server's response to the client will be 0-1-1
   respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp6.)

   To override client delegation, issue the following commands:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, "override-no-update",
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp6 will generate DDNS update requests to
   kea-dhcp-ddns even if the client requests no updates be done. The N-S-O
   flags in the server's response to the client will be 0-1-1.

   To override client delegation, issue the following commands:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

    8.2.18.3. kea-dhcp6 name generation for DDNS update requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp6 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client in the DHCP REQUEST.

   The rules for determining the FQDN option are as follows:

    1. If configured to do so ignore the REQUEST contents and generate a FQDN
       using a configurable prefix and suffix.

    2. Otherwise, using the domain name value from the client FQDN option as
       the candidate name:

         a. If the candidate name is a fully qualified domain name then use
            it.

         b. If the candidate name is a partial (i.e. unqualified) name then
            add a configurable suffix to the name and use the result as the
            FQDN.

         c. If the candidate name is a empty then generate a FQDN using a
            configurable prefix and suffix.

   To instruct kea-dhcp6 to always generate a FQDN, set the parameter
   "replace-client-name" to true:

 "Dhcp6": {
     "dhcp-ddns": {
         "replace-client-name": true,
         ...
     },
     ...
 }

   The prefix used when generating a FQDN is specified by the
   "generated-prefix" parameter. The default value is "myhost". To alter its
   value, simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating a FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When qualifying a partial name, kea-dhcp6 will construct a name with the
   format:

   [candidate-name].[qualifying-suffix].

   where candidate-name is the partial name supplied in the REQUEST. For
   example, if FQDN domain name value was "some-computer" and
   qualifying-suffix "example.com", the generated FQDN would be:

   some-computer.example.com.

   When generating the entire name, kea-dhcp6 will construct name of the
   format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if lease address is 3001:1::70E, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-3001-1--70E.example.com.

8.3. Host reservation in DHCPv6

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve specific, static IPv6
   address or/and prefix for exclusive use by a given client (host) -
   returning client will get the same address or/and prefix every time and
   other clients will never get that address. Note that there may be cases
   when the new reservation has been made for the client for the address or
   prefix being currently in use by another client. We call this situation a
   "conflict". The conflicts get resolved automatically over time as
   described in the subsequent sections. Once conflict is resolved, the
   client will keep receiving the reserved configuration when it renews.

   Another example when the host reservations are applicable is when a host
   that has specific requirements, e.g. a printer that needs additional DHCP
   options or a cable modem needs specific parameters. Yet another possible
   use case for host reservation is to define unique names for hosts.
   Although not all of the presented use cases are implemented yet, Kea
   software will support them in the near future.

   Hosts reservations are defined as parameters for each subnet. Each host
   can be identified by either DUID or its hardware/MAC address. See
   Section 8.9, "MAC/Hardware addresses in DHCPv6" for details. There is an
   optional reservations array in the Subnet6 structure. Each element in that
   array is a structure, that holds information about a single host. In
   particular, such a structure has to have an identifier that uniquely
   identifies a host. In DHCPv6 context, such an identifier is a hardware
   (MAC) address or a DUID. Also, either one or more addresses or prefixes
   should be specified. It is possible to specify a hostname. Additional
   capabilities are planned.

   The following example shows how to reserve addresses and prefixes for
   specific hosts:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "pd-pools": [
             {
                 "prefix": "2001:db8:1:8000::",
                 "prefix-len": 56,
                 "delegated-len": 64
             }
         ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
             },
             {
                 "hw-address": "00:01:02:03:04:05",
                 "ip-addresses": [ "2001:db8:1::101" ]
             },
             {
                 "duid": "01:02:03:04:05:06:07:08:09:0A",
                 "ip-addresses": [ "2001:db8:1::102" ],
                 "prefixes": [ "2001:db8:2:abcd::/64" ],
                 "hostname": "foo.example.com"
             }
         ]
     }
 ]

   This example makes 3 reservations. The first one reserves 2001:db8:1::100
   address for the client using DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The
   second one also reserves an address, but does so using MAC or hardware
   address, rather than DUID. The third example is most advanced. It reserves
   an address, a prefix and a hostname at the same time.

   Note that DHCPv6 allows for a single client to lease multiple addresses
   and multiple prefixes at the same time. In the upcoming Kea releases, it
   will be possible to have multiple addresses and prefixes reserved for a
   single host. Therefore ip-addresses and prefixes are plural and are
   actually arrays. As of 0.9.1 having more than one IPv6 address or prefix
   is only partially supported.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. It is a valid configuration, if such
   definitions are specified in different subnets, though. The reservation
   for a given host should include only one identifier, either DUID or
   hardware address. Defining both for the same host is considered a
   configuration error, but as of 0.9.1 beta, it is not rejected.

   Adding host reservation incurs a performance penalty. In principle, when
   the server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation, has to perform additional checks: not only if the address is
   currently used (if there is a lease for it), but also whether the address
   could be used by someone else (if there is a reservation for it). That
   additional check incurs performance penalty.

  8.3.1. Address/prefix reservation types

   In a typical scenario there's an IPv6 subnet defined with a certain part
   of it dedicated for dynamic address allocation by the DHCPv6 server. There
   may be an additional address space defined for prefix delegation. Those
   dynamic parts are referred to as dynamic pools, address and prefix pools
   or simply pools. In principle, the host reservation can reserve any
   address or prefix that belongs to the subnet. The reservations that
   specify an address that belongs to configured pools are called in-pool
   reservations. In contrast, those that do not belong to dynamic pools are
   called out-of-pool reservations. There is no formal difference in the
   reservation syntax. As of 0.9.1, both reservation types are handled
   uniformly. However, upcoming releases may offer improved performance if
   there are only out-of-pool reservations as the server will be able to skip
   reservation checks when dealing with existing leases. Therefore, system
   administrators are encouraged to use out-of-pool reservations, if
   possible.

  8.3.2. Conflicts in DHCPv6 reservations

   As reservations and lease information are stored in different places,
   conflicts may arise. Consider the following series of events. The server
   has configured the dynamic pool of addresses from the range of
   2001:db8::10 to 2001:db8::20. Host A requests an address and gets
   2001:db8::10. Now the system administrator decides to reserve an address
   for host B. He decides to reserve 2001:db8::10 for that purpose. In
   general, reserving an address that is currently assigned to someone else
   is not recommended, but there are valid use cases where such an operation
   is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If host B boots up and request an address, the server is not able to
   assign the reserved address 2001:db8::10. A naive approach would to be
   immediately remove the lease for host A and create a new one for host B.
   That would not solve the problem, though, because as soon as host B get
   the address, it will detect that the address is already in use by someone
   else (host A) and would send Decline. Therefore in this situation, the
   server has to temporarily assign a different address from the dynamic pool
   (not matching what has been reserved) to host B.

   When the host A renews its address, the server will discover that the
   address being renewed is now reserved for someone else (host B). Therefore
   the server will remove the lease for 2001:db8::10 and select a new address
   and will create a new lease for it. It will send two addresses in its
   response: the old address with lifetimes set to 0 to explicitly indicate
   that it is no longer valid and a new address with non-zero lifetimes. When
   the host B renews its temporarily assigned address, the server will detect
   that the existing lease does not match reservation, so it will release the
   current address host B has and will create a new lease matching the
   reservation. Similar as before, the server will send two addresses: the
   temporarily assigned one with zeroed lifetimes, and the new one that
   matches reservation with proper lifetimes set.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had the host C requested address 2001:db8::10 after the
   reservation was made, the server will propose a different address.

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with existing leases. This procedure takes
   time and will roughly take as long as renew-timer value specified. The
   best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address (note that
   having multiple reservations for the same address is not allowed).

  8.3.3. Reserving a hostname

   When the reservation for the client includes the hostname , the server
   will assign this hostname to the client and send it back in the Client
   FQDN, if the client sent the FQDN option to the server. The reserved
   hostname always takes precedence over the hostname supplied by the client
   (via the FQDN option) or the autogenerated (from the IPv6 address)
   hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "alice-laptop"
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
     "qualifying-suffix": "example.isc.org."
 }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "mark-desktop.example.org."
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
 }

   will result in assigning the "mark-desktop.example.org." hostname to the
   client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".

  8.3.4. Reserving specific options

   Currently it is not possible to specify options in host reservation. Such
   a feature will be added in the upcoming Kea releases.

  8.3.5. Fine Tuning IPv6 Host Reservation

  Note

   reservation-mode in the DHCPv6 server is implemented in Kea 0.9.1 beta,
   but has not been tested and is considered experimental.

   Host reservation capability introduces additional restrictions for the
   allocation engine during lease selection and renewal. In particular, three
   major checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to be not used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address or a prefix, the server has to check whether there's a reservation
   for this host, so the existing (dynamically allocated) address should be
   revoked and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments. Not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     * all - enables all host reservation types. This is the default value.
       This setting is the safest and the most flexible. It allows in-pool
       and out-of-pool reservations. As all checks are conducted, it is also
       the slowest.
     * out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting. Kea 0.9.1 does not sanity check the reservations against
       reservation-mode. Misconfiguration may cause problems.
     * disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   An example configuration that disables reservation looks like follows:

 "Dhcp6": {
     "subnet6": [
         {
         "subnet": "2001:db8:1::/64",
         "reservation-mode": "disabled",
         ...
         }
     ]
 }

8.4. Server Identifier in DHCPv6

   The DHCPv6 protocol uses a "server identifier" (also known as a DUID) for
   clients to be able to discriminate between several servers present on the
   same link. RFC 3315 defines three DUID types: DUID-LLT, DUID-EN and
   DUID-LL. RFC 6355 also defines DUID-UUID. Future specifications may
   introduce new DUID types.

   Kea DHCPv6 server generates a server identifier once, upon the first
   startup, and stores it in a file. This identifier isn't modified across
   restarts of the server (stable identifier).

   Kea follows recommendation from RFC 3315 to use DUID-LLT as a default
   server identifier. However, we have received reports that some deployments
   require different DUID types, and there is a need to administratively
   select both DUID type and/or its contents.

   The server identifier can be configured using parameters within the
   server-id map element in the global scope of the Kea configuration file.
   The following example demonstrates how to select DUID-EN as a server
   identifier:

 "Dhcp6": {
     "server-id": {
         "type": "EN"
     },
     ...
 }

   Currently supported values for type parameter are: "LLT", "EN" and "LL",
   for DUID-LLT, DUID-EN and DUID-LL respectively.

   When a new DUID type is selected the server will generate its value and
   replace any existing DUID in the file. The server will use the new server
   identifier in all future interactions with the clients.

  Note

   If the new server identifier is created after some clients have obtained
   their leases, the clients using old identifier will not be able to renew
   the leases. The server will ignore messages containing the old server
   identifier. Clients will continue sending Renew until they transition to
   rebinding state. In this state they will start sending Rebind messages to
   multicast address and without a server identifier. The server will respond
   to the Rebind messages with a new server identifier and the clients will
   associate the new server identifier with their leases. Although the
   clients will be able to keep their leases and will eventually learn the
   new server identifier, this will be at the cost of increased number of
   renewals and multicast traffic due to a need to rebind. Therefore it is
   recommended to avoid modification of the server identifier type and its
   value if the server has already assigned leases and these leases are still
   valid.

   There are cases when an administrator needs to explicitly specify a DUID
   value, rather than allow the server to generate it. The following example
   demonstrates how to explicitly set all components of a DUID-LLT.

 "Dhcp6": {
     "server-id": {
         "type": "LLT",
         "htype": 8,
         "identifier": "A65DC7410F05",
         "time": 2518920166
     },
     ...
 }

   where:

     * htype is a 16-bit unsigned value specifying hardware type,
     * identifier is a link layer address, specified as a string of
       hexadecimal digits,
     * time is a 32-bit unsigned time value.

   The hexadecimal representation of the DUID generated as a result of the
   configuration specified above will be:

 00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
 ------------------------------------------
 |type|htype|   time    |   identifier    |

   It is allowed to use special value of 0 for "htype" and "time", which
   indicates that the server should use ANY value for these components. If
   the server already uses a DUID-LLT it will use the values from this DUID.
   If the server uses a DUID of a different type or doesn't use any DUID yet,
   it will generate these values. Similarly, if the "identifier" is assigned
   an empty string, the value of the identifier will be generated. Omitting
   any of these parameters is equivalent to setting them to those special
   values.

   For example, the following configuration:

 "Dhcp6": {
     "server-id": {
         "type": "LLT",
         "htype": 0,
         "identifier": "",
         "time": 2518920166
     },
     ...
 }

   indicates that the server should use ANY link layer address and hardware
   type. If the server is already using DUID-LLT it will use link layer
   address and hardware type from the existing DUID. If the server is not
   using any DUID yet, it will use link layer address and hardware type from
   one of the available network interfaces. The server will use explicit
   value of time. If it is different than a time value present in the
   currently used DUID, this value will be replaced. This will effectively
   cause modification of the current server identifier.

   The following example demonstrates an explicit configuration of a DUID-EN:

 "Dhcp6": {
     "server-id": {
         "type": "EN",
         "enterprise-id": 2495,
         "identifier": "87ABEF7A5BB545"
     },
     ...
 }

   where:

     * enterprise-id is a 32-bit unsigned value holding enterprise number,
     * identifier is a variable length identifier within DUID-EN.

   The hexadecimal representation of the DUID-EN created according to the
   configuration above is:

 00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
 --------------------------------------
 |type|  ent-id   |    identifier     |

   As in the case of the DUID-LLT, special values can be used for the
   configuration of the DUID-EN. If the "enterprise-id" is 0, the server will
   use a value from the existing DUID-EN. If the server is not using any DUID
   or the existing DUID has a different type, the ISC enterprise id will be
   used. When an empty string is used for "identifier", the identifier from
   the existing DUID-EN will be used. If the server is not using any DUID-EN
   the new 6-bytes long identifier will be generated.

   DUID-LL is configured in the same way as DUID-LLT with an exception that
   the time parameter has no effect for DUID-LL, because this DUID type only
   comprises a hardware type and link layer address. The following example
   demonstrates how to configure DUID-LL:

 "Dhcp6": {
     "server-id": {
         "type": "LL",
         "htype": 8,
         "identifier": "A65DC7410F05"
     },
     ...
 }

   which will result in the following server identifier:

 00:03:00:08:A6:5D:C7:41:0F:05
 ------------------------------
 |type|htype|   identifier   |

   Server stores a generated server identifier in the following location:
   [kea-install-dir]/var/kea/kea-dhcp6-serverid .

   In some uncommon deployments where no stable storage is available, it is
   desired to configure the server to not try to store the server identifier
   on the stable storage. It is controlled by the value of persist boolean
   parameter:

 "Dhcp6": {
     "server-id": {
         "type": "EN",
         "enterprise-id": 2495,
         "identifier": "87ABEF7A5BB545",
         "persist": false
     },
     ...
 }

   The default value of the "persist" parameter is true which configures the
   server to store the server identifier on a disk.

   In the example above, the server is configured to not store the generated
   server identifier on a disk. But, if the server identifier is not modified
   in the configuration the same value will be used after server restart,
   because entire server identifier is explicitly specified in a
   configuration.

8.5. Stateless DHCPv6 (Information-Request Message)

   Typically DHCPv6 is used to assign both addresses and options. These
   assignments (leases) have state that changes over time, hence their name,
   stateful. DHCPv6 also supports a stateless mode, where clients request
   configuration options only. This mode is considered lightweight from the
   server perspective, as it does not require any state tracking; hence its
   name.

   The Kea server supports stateless mode. Clients can send
   Information-Request messages and the server will send back answers with
   the requested options (providing the options are available in the server
   configuration). The server will attempt to use per-subnet options first.
   If that fails - for whatever reason - it will then try to provide options
   defined in the global scope.

   Stateless and stateful mode can be used together. No special configuration
   directives are required to handle this. Simply use the configuration for
   stateful clients and the stateless clients will get just options they
   requested.

   This usage of global options allows for an interesting case. It is
   possible to run a server that provides just options and no addresses or
   prefixes. If the options have the same value in each subnet, the
   configuration can define required options in the global scope and skip
   subnet definitions altogether. Here's a simple example of such a
   configuration:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "ethX" ]
     },
     "option-data": [ {
         "name": "dns-servers",
         "data": "2001:db8::1, 2001:db8::2"
     } ],
     "lease-database": { "type": "memfile" }
  }

   This very simple configuration will provide DNS server information to all
   clients in the network, regardless of their location. Note the
   specification of the memfile lease database: this is required since, as of
   version 0.9.1, Kea requires a lease database to be specified even if it is
   not used.

8.6. Support for RFC 7550

   The RFC 7550 has introduced some changes to the DHCPv6 protocol to resolve
   a few issues with the coexistence of multiple stateful options in the
   messages sent between the clients and servers.

   The typical example is when the client, such as a requesting router,
   requests an allocation of both addresses and prefixes when it performs the
   4-way (SARR) exchange with the server. If the server is not configured to
   allocate any prefixes but it can allocate some addresses, it will respond
   with the IA_NA(s) containing allocated addresses and the IA_PD(s)
   containing the NoPrefixAvail status code. If the client can operate
   without prefixes it may transition to the 'bound' state when it sends
   Renew/Rebind messages to the server, according to the T1 and T2 times, to
   extend the lifetimes of the allocated addresses. If the client is still
   interested in obtaining prefixes from the server it may also include IA_PD
   in the Renew/Rebind to request allocation of the prefixes. If the server
   still cannot allocate the prefixes, it will respond with the IA_PD(s)
   containing NoPrefixAvail status code. However, if the server can now
   allocate the prefixes it will do so, and send them in the IA_PD(s) to the
   client. Allocation of leases during the Renew/Rebind was not supported in
   the RFC 3315 and RFC 3633, and has been introduced in RFC 7550. Kea
   supports this new behavior and it doesn't provide any configuration
   mechanisms to disable it.

   The following are the other behaviors specified in the RFC 7550 supported
   by the Kea DHCPv6 server:

     * set T1/T2 timers to the same value for all stateful (IA_NA and IA_PD)
       options to facilitate renewal of all client's leases at the same time
       (in a single message exchange),
     * NoAddrsAvail and NoPrefixAvail status codes are placed in the IA_NA
       and IA_PD options in the Advertise message, rather than as the top
       level options.

8.7. Using specific relay agent for a subnet

   The relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has a global IPv6
   address configured on the interface that belongs to the subnet from which
   the server will assign addresses. In the typical case, the server is able
   to use the IPv6 address inserted by the relay (in the link-addr field in
   RELAY-FORW message) to select the appropriate subnet.

   However, that is not always the case. The relay address may not match the
   subnet in certain deployments. This usually means that there is more than
   one subnet allocated for a given link. The two most common examples where
   this is the case are long lasting network renumbering (where both old and
   new address space is still being used) and a cable network. In a cable
   network both cable modems and the devices behind them are physically
   connected to the same link, yet they use distinct addressing. In such
   case, the DHCPv6 server needs additional information (like the value of
   interface-id option or IPv6 address inserted in the link-addr field in
   RELAY-FORW message) to properly select an appropriate subnet.

   The following example assumes that there is a subnet 2001:db8:1::/64 that
   is accessible via relay that uses 3000::1 as its IPv6 address. The server
   will be able to select this subnet for any incoming packets that came from
   a relay that has an address in 2001:db8:1::/64 subnet. It will also select
   that subnet for a relay with address 3000::1.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-address": "3000::1"
              }
         }
     ]
 }

8.8. Segregating IPv6 clients in a cable network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 8.7, "Using specific relay agent for a subnet" with
   client classification, explained in Chapter 12, Client Classification. One
   specific example is a cable network, where typically modems get addresses
   from a different subnet than all devices connected behind them.

   Let's assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 3000::/64 subnet, while everything
   connected behind modems should get addresses from another subnet
   (2001:db8:1::/64). The CMTS that acts as a relay an uses address 3000::1.
   The following configuration can serve that configuration:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "3000::/64",
             "pools": [
                 { "pool": "3000::2 - 3000::ffff" }
             ],
             "client-class": "VENDOR_CLASS_docsis3.0",
             "relay": {
                 "ip-address": "3000::1"
             }
         },

         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-address": "3000::1"
              }
         }
     ]
 }

8.9. MAC/Hardware addresses in DHCPv6

   MAC/hardware addresses are available in DHCPv4 messages from the clients
   and administrators frequently use that information to perform certain
   tasks, like per host configuration, address reservation for specific MAC
   addresses and other. Unfortunately, the DHCPv6 protocol does not provide
   any completely reliable way to retrieve that information. To mitigate that
   issue a number of mechanisms have been implemented in Kea that attempt to
   gather that information. Each of those mechanisms works in certain cases,
   but may fail in other cases. Whether the mechanism works or not in the
   particular deployment is somewhat dependent on the network topology and
   the technologies used.

   Kea allows for configuration which of the supported methods should be used
   and in which order. This configuration may be considered a fine tuning of
   the DHCP deployment. In a typical deployment the default value of "any" is
   sufficient and there is no need to select specific methods. Changing the
   value of this parameter is the most useful in cases when an administrator
   wants to disable certain method, e.g. if the administrator trusts the
   network infrastructure more than the information provided by the clients
   themselves, the administrator may prefer information provided by the
   relays over that provided by the clients. The format of this parameter is
   as follows:

 "Dhcp6": {
     "mac-sources": [ "method1", "method2", "method3", ... ],

     "subnet6": [ ... ],

     ...
 }

   When not specified, a special value of any is used, which instructs the
   server to attempt to use all the methods in sequence and use value
   returned by the first one that succeeds.

   Supported methods are:

     * any - not an actual method, just a keyword that instructs Kea to try
       all other methods and use the first one that succeeds. This is the
       default operation if no mac-sources are defined.
     * raw - In principle, a DHCPv6 server could use raw sockets to receive
       incoming traffic and extract MAC/hardware address information. This is
       currently not implemented for DHCPv6 and this value has no effect.
     * duid - DHCPv6 uses DUID identifiers instead of MAC addresses. There
       are currently four DUID types defined, with two of them (DUID-LLT,
       which is the default one and DUID-LL) convey MAC address information.
       Although RFC 3315 forbids it, it is possible to parse those DUIDs and
       extract necessary information from them. This method is not completely
       reliable, as clients may use other DUID types, namely DUID-EN or
       DUID-UUID.
     * ipv6-link-local - Another possible acquisition method comes from the
       source IPv6 address. In typical usage, clients are sending their
       packets from IPv6 link-local addresses. There's a good chance that
       those addresses are based on EUI-64, which contains MAC address. This
       method is not completely reliable, as clients may use other link-local
       address types. In particular, privacy extensions, defined in RFC 4941,
       do not use MAC addresses. Also note that successful extraction
       requires that the address's u-bit must be set to 1 and its g-bit set
       to 0, indicating that it is an interface identifier as per RFC 2373,
       section 2.5.1.
     * client-link-addr-option - One extension defined to alleviate missing
       MAC issues is client link-layer address option, defined in RFC 6939.
       This is an option that is inserted by a relay and contains information
       about client's MAC address. This method requires a relay agent that
       supports the option and is configured to insert it. This method is
       useless for directly connected clients. This parameter can also be
       specified as rfc6939, which is an alias for client-link-addr-option.
     * remote-id - RFC 4649 defines remote-id option that is inserted by a
       relay agent. Depending on the relay agent configuration, the inserted
       option may convey client's MAC address information. This parameter can
       also be specified as rfc4649, which is an alias for remote-id.
     * subscriber-id - Another option that is somewhat similar to the
       previous one is subscriber-id, defined in RFC 4580. It is, too,
       inserted by a relay agent that is configured to insert it. This
       parameter can also be specified as rfc4580, which is an alias for
       subscriber-id. This method is currently not implemented.
     * docsis-cmts - Yet another possible source of MAC address information
       are DOCSIS options inserted by a CMTS that acts as a DHCPv6 relay
       agent in cable networks. This method attempts to extract MAC address
       information from suboption 1026 (cm mac) of the vendor specific option
       with vendor-id=4491. This vendor option is extracted from the
       relay-forward message, not the original client's message.
     * docsis-modem - Yet another possible source of MAC address information
       are DOCSIS options inserted by the cable modem itself. This method
       attempts to extract MAC address information from suboption 36 (device
       id) of the vendor specific option with vendor-id=4491. This vendor
       option is extracted from the original client's message, not from any
       relay options.

8.10. Duplicate Addresses (DECLINE support)

   The DHCPv6 server is configured with a certain pool of addresses that it
   is expected to hand out to the DHCPv6 clients. It is assumed that the
   server is authoritative and has complete jurisdiction over those
   addresses. However, due to various reasons, such as misconfiguration or a
   faulty client implementation that retains its address beyond the valid
   lifetime, there may be devices connected that use those addresses without
   the server's approval or knowledge.

   Such an unwelcome event can be detected by legitimate clients (using
   Duplicate Address Detection) and reported to the DHCPv6 server using a
   DECLINE message. The server will do a sanity check (if the client
   declining an address really was supposed to use it), then will a conduct
   clean up operation and confirm it by sending back a REPLY message. Any DNS
   entries related to that address will be removed, the fact will be logged
   and hooks will be triggered. After that is done, the address will be
   marked as declined (which indicates that it is used by an unknown entity
   and thus not available for assignment to anyone) and a probation time will
   be set on it. Unless otherwise configured, the probation period lasts 24
   hours. After that period, the server will recover the lease, i.e. put it
   back into the available state. The address will be available for
   assignment again. It should be noted that if the underlying issue of a
   misconfigured device is not resolved, the duplicate address scenario will
   repeat. On the other hand, it provides an opportunity to recover from such
   an event automatically, without any sysadmin intervention.

   To configure the decline probation period to a value different than the
   default, the following syntax can be used:

   "Dhcp6": {
     "decline-probation-period": 3600,
     "subnet6": [ ... ],
     ...
 }

   The parameter is expressed in seconds, so the example above will instruct
   the server to recycle declined leases after an hour.

   There are several statistics and hook points associated with the Decline
   handling procedure. The lease6_decline hook is triggered after the
   incoming Decline message has been sanitized and the server is about to
   decline the lease. The declined-addresses statistic is increased after the
   hook returns (both global and subnet specific variants).

   Once the probation time elapses, the declined lease is recovered using the
   standard expired lease reclamation procedure, with several additional
   steps. In particular, both declined-addresses statistics (global and
   subnet specific) are decreased. At the same time,
   reclaimed-declined-addresses statistics (again in two variants, global and
   subnet specific) are increased.

   Note about statistics: The server does not decrease assigned-addresses
   statistics when a DECLINE message is received and processed successfully.
   While technically a declined address is no longer assigned, the primary
   usage of the assigned-addresses statistic is to monitor pool utilization.
   Most people would forget to include declined-addresses in the calculation,
   and simply do assigned-addresses/total-addresses. This would have a bias
   towards under-representing pool utilization. As this has a potential for
   major issues, we decided not to decrease assigned addresses immediately
   after receiving Decline, but to do it later when we recover the address
   back to the available pool.

8.11. Statistics in DHCPv6 server

  Note

   This section describes DHCPv6-specific statistics. For a general overview
   and usage of statistics, see Chapter 14, Statistics.

   The DHCPv6 server supports the following statistics:

   Table 8.4. DHCPv6 Statistics

  +----------------------------------------------------------------------------+
  |               Statistic               |Data Type|Description               |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv6 packets  |
  |                                       |         |received. This includes   |
  |             pkt6-received             | integer |all packets: valid, bogus,|
  |                                       |         |corrupted, rejected etc.  |
  |                                       |         |This statistic is expected|
  |                                       |         |to grow rapidly.          |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of incoming packets|
  |                                       |         |that were dropped. Exact  |
  |                                       |         |reason for dropping       |
  |                                       |         |packets is logged, but the|
  |                                       |         |most common reasons may   |
  |                                       |         |be: an unacceptable or not|
  |           pkt6-receive-drop           | integer |supported packet type,    |
  |                                       |         |direct responses are      |
  |                                       |         |forbidden, the server-id  |
  |                                       |         |sent by the client does   |
  |                                       |         |not match the server's    |
  |                                       |         |server-id or the packet is|
  |                                       |         |malformed.                |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of incoming packets|
  |                                       |         |that could not be parsed. |
  |                                       |         |A non-zero value of this  |
  |                                       |         |statistic indicates that  |
  |                                       |         |the server received a     |
  |           pkt6-parse-failed           | integer |malformed or truncated    |
  |                                       |         |packet. This may indicate |
  |                                       |         |problems in your network, |
  |                                       |         |faulty clients, faulty    |
  |                                       |         |relay agents or server    |
  |                                       |         |code bug.                 |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of SOLICIT packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |                                       |         |increase means that       |
  |         pkt6-solicit-received         | integer |clients that just booted  |
  |                                       |         |started their             |
  |                                       |         |configuration process and |
  |                                       |         |their initial packets     |
  |                                       |         |reached your server.      |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of ADVERTISE       |
  |                                       |         |packets received.         |
  |                                       |         |Advertise packets are sent|
  |                                       |         |by the server and the     |
  |                                       |         |server is never expected  |
  |                                       |         |to receive them. A        |
  |                                       |         |non-zero value of this    |
  |        pkt6-advertise-received        | integer |statistic indicates an    |
  |                                       |         |error occurring in the    |
  |                                       |         |network. One likely cause |
  |                                       |         |would be a misbehaving    |
  |                                       |         |relay agent that          |
  |                                       |         |incorrectly forwards      |
  |                                       |         |ADVERTISE messages towards|
  |                                       |         |the server, rather back to|
  |                                       |         |the clients.              |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REQUEST packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |                                       |         |increase means that       |
  |         pkt6-request-received         | integer |clients that just booted  |
  |                                       |         |received the server's     |
  |                                       |         |response (ADVERTISE),     |
  |                                       |         |accepted it and are now   |
  |                                       |         |requesting an address     |
  |                                       |         |(REQUEST).                |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REPLY packets   |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to remain zero|
  |                                       |         |at all times, as REPLY    |
  |                                       |         |packets are sent by the   |
  |                                       |         |server and the server is  |
  |                                       |         |never expected to receive |
  |          pkt6-reply-received          | integer |them. A non-zero value    |
  |                                       |         |indicates an error. One   |
  |                                       |         |likely cause would be a   |
  |                                       |         |misbehaving relay agent   |
  |                                       |         |that incorrectly forwards |
  |                                       |         |REPLY messages towards the|
  |                                       |         |server, rather back to the|
  |                                       |         |clients.                  |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of RENEW packets   |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |          pkt6-renew-received          | integer |increase means that       |
  |                                       |         |clients received their    |
  |                                       |         |addresses and prefixes and|
  |                                       |         |are trying to renew them. |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REBIND packets  |
  |                                       |         |received. A non-zero value|
  |                                       |         |indicates that clients    |
  |                                       |         |didn't receive responses  |
  |                                       |         |to their RENEW messages   |
  |                                       |         |(regular lease renewal    |
  |         pkt6-rebind-received          | integer |mechanism) and are        |
  |                                       |         |attempting to find any    |
  |                                       |         |server that is able to    |
  |                                       |         |take over their leases. It|
  |                                       |         |may mean that some        |
  |                                       |         |server's REPLY messages   |
  |                                       |         |never reached the clients.|
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of RELEASE packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow when a|
  |                                       |         |device is being shut down |
  |                                       |         |in the network. It        |
  |                                       |         |indicates that the address|
  |         pkt6-release-received         | integer |or prefix assigned is     |
  |                                       |         |reported as no longer     |
  |                                       |         |needed. Note that many    |
  |                                       |         |devices, especially       |
  |                                       |         |wireless, do not send     |
  |                                       |         |RELEASE, because of design|
  |                                       |         |choice or due to moving   |
  |                                       |         |out of range.             |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DECLINE packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to remain     |
  |                                       |         |close to zero. Its        |
  |                                       |         |increase means that a     |
  |                                       |         |client leased an address, |
  |                                       |         |but discovered that the   |
  |         pkt6-decline-received         | integer |address is currently used |
  |                                       |         |by an unknown device in   |
  |                                       |         |your network. If this     |
  |                                       |         |statistic is growing, it  |
  |                                       |         |may indicate misconfigured|
  |                                       |         |server or devices that    |
  |                                       |         |have statically assigned  |
  |                                       |         |conflicting addresses.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of                 |
  |                                       |         |INFORMATION-REQUEST       |
  |                                       |         |packets received. This    |
  |                                       |         |statistic is expected to  |
  |                                       |         |grow if there are devices |
  |                                       |         |that are using stateless  |
  |       pkt6-infrequest-received        | integer |DHCPv6.                   |
  |                                       |         |INFORMATION-REQUEST       |
  |                                       |         |messages are used by      |
  |                                       |         |clients that request      |
  |                                       |         |stateless configuration,  |
  |                                       |         |i.e. options and          |
  |                                       |         |parameters other than     |
  |                                       |         |addresses or prefixes.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of packets received|
  |                                       |         |of an unknown type.       |
  |                                       |         |Non-zero value of this    |
  |                                       |         |statistic indicates that  |
  |         pkt6-unknown-received         | integer |the server received a     |
  |                                       |         |packet that it wasn't able|
  |                                       |         |to recognize: either with |
  |                                       |         |unsupported type or       |
  |                                       |         |possibly malformed.       |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv6 packets  |
  |                                       |         |sent. This statistic is   |
  |                                       |         |expected to grow every    |
  |                                       |         |time the server transmits |
  |                                       |         |a packet. In general, it  |
  |                                       |         |should roughly match      |
  |                                       |         |pkt6-received, as most    |
  |               pkt6-sent               | integer |incoming packets cause the|
  |                                       |         |server to respond. There  |
  |                                       |         |are exceptions (e.g.      |
  |                                       |         |server receiving a REQUEST|
  |                                       |         |with server-id matching   |
  |                                       |         |other server), so do not  |
  |                                       |         |worry, if it is lesser    |
  |                                       |         |than pkt6-received.       |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of ADVERTISE       |
  |                                       |         |packets sent. This        |
  |                                       |         |statistic is expected to  |
  |                                       |         |grow in most cases after a|
  |                                       |         |SOLICIT is processed.     |
  |          pkt6-advertise-sent          | integer |There are certain         |
  |                                       |         |uncommon, but valid cases |
  |                                       |         |where incoming SOLICIT is |
  |                                       |         |dropped, but in general   |
  |                                       |         |this statistic is expected|
  |                                       |         |to be close to            |
  |                                       |         |pkt6-solicit-received.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REPLY packets   |
  |                                       |         |sent. This statistic is   |
  |                                       |         |expected to grow in most  |
  |                                       |         |cases after a SOLICIT     |
  |                                       |         |(with rapid-commit),      |
  |            pkt6-reply-sent            | integer |REQUEST, RENEW, REBIND,   |
  |                                       |         |RELEASE, DECLINE or       |
  |                                       |         |INFORMATION-REQUEST is    |
  |                                       |         |processed. There are      |
  |                                       |         |certain cases where there |
  |                                       |         |is no response.           |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |total number of NA        |
  |                                       |         |addresses available for   |
  |                                       |         |DHCPv6 management for a   |
  |                                       |         |given subnet. In other    |
  |                                       |         |words, this is the sum of |
  |                                       |         |all addresses in all      |
  |                                       |         |configured pools. This    |
  |                                       |         |statistic changes only    |
  |                                       |         |during configuration      |
  |         subnet[id].total-nas          | integer |changes. Note it does not |
  |                                       |         |take into account any     |
  |                                       |         |addresses that may be     |
  |                                       |         |reserved due to host      |
  |                                       |         |reservation. The id is the|
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately. This statistic|
  |                                       |         |is reset during a         |
  |                                       |         |reconfiguration event.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of NA addresses in |
  |                                       |         |a given subnet that are   |
  |                                       |         |assigned. This statistic  |
  |                                       |         |increases every time a new|
  |                                       |         |lease is allocated (as a  |
  |                                       |         |result of receiving a     |
  |                                       |         |REQUEST message) and is   |
  |                                       |         |decreased every time a    |
  |        subnet[id].assigned-nas        | integer |lease is released (a      |
  |                                       |         |RELEASE message is        |
  |                                       |         |received) or expires. The |
  |                                       |         |id is the subnet-id of a  |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately.   |
  |                                       |         |This statistic is reset   |
  |                                       |         |during a reconfiguration  |
  |                                       |         |event.                    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |total number of PD        |
  |                                       |         |prefixes available for    |
  |                                       |         |DHCPv6 management for a   |
  |                                       |         |given subnet. In other    |
  |                                       |         |words, this is the sum of |
  |                                       |         |all prefixes in all       |
  |                                       |         |configured pools. This    |
  |                                       |         |statistic changes only    |
  |                                       |         |during configuration      |
  |         subnet[id].total-pds          | integer |changes. Note it does not |
  |                                       |         |take into account any     |
  |                                       |         |prefixes that may be      |
  |                                       |         |reserved due to host      |
  |                                       |         |reservation. The id is the|
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately. This statistic|
  |                                       |         |is reset during a         |
  |                                       |         |reconfiguration event.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of PD prefixes in a|
  |                                       |         |given subnet that are     |
  |                                       |         |assigned. This statistic  |
  |                                       |         |increases every time a new|
  |                                       |         |lease is allocated (as a  |
  |                                       |         |result of receiving a     |
  |                                       |         |REQUEST message) and is   |
  |                                       |         |decreased every time a    |
  |        subnet[id].assigned-pds        | integer |lease is released (a      |
  |                                       |         |RELEASE message is        |
  |                                       |         |received) or expires. The |
  |                                       |         |id is the subnet-id of a  |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately.   |
  |                                       |         |This statistic is reset   |
  |                                       |         |during a reconfiguration  |
  |                                       |         |event.                    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that are currently        |
  |                                       |         |declined. This statistic  |
  |                                       |         |counts the number of      |
  |                                       |         |leases currently          |
  |                                       |         |unavailable. Once a lease |
  |                                       |         |is recovered, this        |
  |                                       |         |statistic will be         |
  |          declined-addresses           | integer |decreased. Ideally, this  |
  |                                       |         |statistic should be zero. |
  |                                       |         |If this statistic is      |
  |                                       |         |non-zero (or worse        |
  |                                       |         |increasing), a network    |
  |                                       |         |administrator should      |
  |                                       |         |investigate if there is a |
  |                                       |         |misbehaving device in his |
  |                                       |         |network. This is a global |
  |                                       |         |statistic that covers all |
  |                                       |         |subnets.                  |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that are currently        |
  |                                       |         |declined in a given       |
  |                                       |         |subnet. This statistic    |
  |                                       |         |counts the number of      |
  |                                       |         |leases currently          |
  |                                       |         |unavailable. Once a lease |
  |                                       |         |is recovered, this        |
  |                                       |         |statistic will be         |
  |                                       |         |decreased. Ideally, this  |
  |     subnet[id].declined-addresses     | integer |statistic should be zero. |
  |                                       |         |If this statistic is      |
  |                                       |         |non-zero (or worse        |
  |                                       |         |increasing), a network    |
  |                                       |         |administrator should      |
  |                                       |         |investigate if there is a |
  |                                       |         |misbehaving device in his |
  |                                       |         |network. The id is the    |
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately.               |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that were declined, but   |
  |                                       |         |have now been recovered.  |
  |                                       |         |Unlike declined-addresses,|
  |                                       |         |this statistic never      |
  |     reclaimed-declined-addresses      | integer |decreases. It can be used |
  |                                       |         |as a long term indicator  |
  |                                       |         |of how many actual valid  |
  |                                       |         |Declines were processed   |
  |                                       |         |and recovered from. This  |
  |                                       |         |is a global statistic that|
  |                                       |         |covers all subnets.       |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that were declined, but   |
  |                                       |         |have now been recovered.  |
  |                                       |         |Unlike declined-addresses,|
  |                                       |         |this statistic never      |
  |                                       |         |decreases. It can be used |
  |subnet[id].reclaimed-declined-addresses| integer |as a long term indicator  |
  |                                       |         |of how many actual valid  |
  |                                       |         |Declines were processed   |
  |                                       |         |and recovered from. The id|
  |                                       |         |is the subnet-id of a     |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately.   |
  +----------------------------------------------------------------------------+

8.12. Management API for the DHCPv6 server

   Management API has been introduced in Kea 0.9.2-beta. It allows issuing
   specific management commands, like statistics retrieval, reconfiguration
   or shutdown. For more details, see Chapter 15, Management API. Currently
   the only supported communication channel type is UNIX stream socket. By
   default there are no sockets open. To instruct Kea to open a socket, the
   following entry in the configuration file can be used:

 "Dhcp6": {
     "control-socket": {
         "socket-type": "unix",
         "socket-name": "/path/to/the/unix/socket"
     },

     "subnet6": [
         ...
     ],
     ...
 }

   The length of the path specified by the socket-name parameter is
   restricted by the maximum length for the unix socket name on your
   operating system, i.e. the size of the sun_path field in the sockaddr_un
   structure, decreased by 1. This value varies on different operating
   systems between 91 and 107 characters. The typical values are 107 on Linux
   and 103 on FreeBSD.

   Communication over control channel is conducted using JSON structures. See
   the Control Channel section in the Kea Developer's Guide for more details.

   DHCPv6 server supports statistic-get, statistic-reset, statistic-remove,
   statistic-get-all, statistic-reset-all and statistic-remove-all, specified
   in Section 14.3, "Commands for Manipulating Statistics". It also supports
   list-commands and shutdown, specified in Section 15.3.2, "list-commands
   command" and Section 15.3.3, "shutdown command", respectively.

8.13. Supported DHCPv6 Standards

   The following standards are currently supported:

     * Dynamic Host Configuration Protocol for IPv6, RFC 3315: Supported
       messages are SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND,
       INFORMATION-REQUEST, CONFIRM and REPLY.
     * IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP)
       version 6, RFC 3633: Supported options are IA_PD and IA_PREFIX. Also
       supported is the status code NoPrefixAvail.
     * DNS Configuration options for Dynamic Host Configuration Protocol for
       IPv6 (DHCPv6), RFC 3646: Supported option is DNS_SERVERS.
     * The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent
       Remote-ID Option, RFC 4649: REMOTE-ID option is supported.
     * The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully
       Qualified Domain Name (FQDN) Option, RFC 4704: Supported option is
       CLIENT_FQDN.
     * Relay-Supplied DHCP Options, RFC 6422: Full functionality is
       supported: OPTION_RSOO, ability of the server to echo back the
       options, checks whether an option is RSOO-enabled, ability to mark
       additional options as RSOO-enabled.
     * Client Link-Layer Address Option in DHCPv6, RFC 6939: Supported option
       is client link-layer address option.
     * Issues and Recommendations with Multiple Stateful DHCPv6 Options, RFC
       7550: All recommendations related to the DHCPv6 server operation are
       supported.

8.14. DHCPv6 Server Limitations

   These are the current limitations and known problems with the DHCPv6
   server software. Most of them are reflections of the early stage of
   development and should be treated as "not implemented yet", rather than
   actual limitations.

     * On-line configuration has some limitations. Adding new subnets or
       modifying existing ones work, as is removing the last subnet from the
       list. However, removing non-last (e.g. removing subnet 1,2 or 3 if
       there are 4 subnets configured) will cause issues. The problem is
       caused by simplistic subnet-id assignment. The subnets are always
       numbered, starting from 1. That subnet-id is then used in leases that
       are stored in the lease database. Removing non-last subnet will cause
       the configuration information to mismatch data in the lease database.
       It is possible to manually update subnet-id fields in MySQL or
       PostgreSQL database, but it is awkward and error prone process. A
       better reconfiguration support is planned.

     * The server will allocate, renew or rebind a maximum of one lease for a
       particular IA option (IA_NA or IA_PD) sent by a client. RFC 3315 and
       RFC 3633 allow for multiple addresses or prefixes to be allocated for
       a single IA.
     * Temporary addresses are not supported.
     * Duplication report (DECLINE) and client reconfiguration (RECONFIGURE)
       are not yet supported.

                Chapter 9. Lease Expiration in DHCPv4 and DHCPv6

   Table of Contents

   9.1. Lease Reclamation

   9.2. Configuring Leases Reclamation

   9.3. Configuring Lease Affinity

   9.4. Default Configuration Values for Leases Reclamation

   9.5. Reclaiming Expired Leases with Command

   The primary role of the DHCP server is to assign addresses and/or delegate
   prefixes to DHCP clients. These addresses and prefixes are often referred
   to as 'leases'. Leases are typically assigned to clients for a finite
   amount of time, known as 'valid lifetime'. DHCP clients who wish to
   continue using their assigned leases, will periodically renew them by
   sending the appropriate message to the DHCP server. The DHCP server
   records the time when these leases are renewed and calculates new
   expiration times for them.

   If the client does not renew a lease before its valid lifetime elapses,
   the lease is considered expired. There are many situations when the client
   may cease lease renewals. A common scenario is when the machine running
   the client shuts down for an extended period of time.

   The process through which the DHCP server makes expired leases available
   for reassignment is referred to as "lease reclamation" and expired leases
   returned to availability through this process are referred to as
   "reclaimed". The DHCP server should reclaim an expired lease as soon as it
   detects that it has expired. One way in which the server may detect
   expiration is when it is trying to allocate a lease to a client and finds
   this lease already present in the database but expired. Another way the
   server detects expired leases is by periodically querying the lease
   database for them. Regardless of how an expired lease is detected, before
   it my assigned to a client, it must be reclaimed. This chapter explains
   how to configure the server to periodically query for the expired leases
   and how to minimize the impact of the periodic leases reclamation process
   on the server's responsiveness. Finally, 'lease affinity', which provides
   the means to assign the same lease to the returning client after its lease
   has expired, is explained.

   Although, all configuration examples in this section are provided for the
   DHCPv4 server, the same parameters may be used for the DHCPv6 server
   configuration.

9.1. Lease Reclamation

   Lease reclamation is the process through which an expired lease becomes
   available for assignment to the same or a different client. This process
   involves the following steps for each reclaimed lease:

     * Invoke callouts for the lease4_expire or lease6_expire hook points, if
       hook libraries supporting those callouts are currently loaded.
     * Update DNS, i.e. remove any DNS entries associated with the expired
       lease.
     * Update lease information in the lease database to indicate that the
       lease is now available for re-assignment.
     * Update statistics of the server, which includes increasing the number
       of reclaimed leases and decreasing the number of assigned addresses or
       delegated prefixes etc.

   Please refer to Chapter 10, The DHCP-DDNS Server to see how to configure
   DNS updates in Kea, and to Chapter 13, Hooks Libraries for information
   about using hooks libraries.

9.2. Configuring Leases Reclamation

   Kea can be configured to periodically detect and reclaim expired leases.
   During this process the lease entries in the database are modified or
   removed. Therefore the server will not process incoming DHCP messages to
   avoid issues with concurrent access to database information. As a result,
   the server will be unresponsive while lease reclamation is performed. DHCP
   queries will accumulate and responses will be sent once the leases
   reclamation cycle is complete.

   In deployments where response time is critical, administrators may wish to
   minimize the interruptions in service caused by lease reclamation. Toward
   this end, Kea provides configuration parameters to control: the frequency
   of lease reclamation cycles, the maximum number of leases processed in a
   single reclamation cycle, and the maximum amount of time a single
   reclamation cycle is allowed to run before being interrupted. The
   following examples demonstrate how these parameters can be used:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 5,
         "max-reclaim-leases": 0,
         "max-reclaim-time": 0,
         "flush-reclaimed-timer-wait-time": 0,
     },

     ...
 }

   The first parameter is expressed in seconds and specifies an interval
   between the two consecutive lease reclamation cycles. This is explained on
   the following diagram.


 |  c1  |            | c2 |            |c3|            | c4 |
 |<---->|<---------->|<-->|<---------->|<>|<---------->|<-->|
 ---------------------------------------------------------------->
 |      |     5s     |    |     5s     |  |     5s     |    | time


   This diagram shows 4 leases reclamation cycles of variable duration. Note
   that the duration of the reclamation cycle depends on the number of
   expired leases detected and processed in the particular cycle. This
   duration is also usually significantly shorter than the interval between
   the cycles.

   According to the reclaim-timer-wait-time the server keeps fixed intervals
   of 5 seconds between the end of one cycle and the start of the next cycle.
   This guarantees the presence of 5s long periods during which the server
   remains responsive to DHCP queries and does not perform leases
   reclamation. The max-reclaim-leases and max-reclaim-time are set to 0,
   which implies that there is no restriction on the maximum number of leases
   reclaimed in the particular cycle, or the maximum duration of each cycle.

   In deployments with high lease pool utilization, relatively short valid
   lifetimes, and frequently disconnecting clients which allow leases to
   expire; the number of expired leases requiring reclamation at any given
   time may rise significantly. In this case it is often desirable to apply
   restrictions on the maximum duration of a reclamation cycle or the maximum
   number of leases reclaimed in a cycle. The following configuration
   demonstrates how this can be done:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 3,
         "max-reclaim-leases": 100,
         "max-reclaim-time": 50,
         "unwarned-reclaim-cycles": 10,
         "flush-reclaimed-timer-wait-time": 0,
     },

     ...
 }


   The max-reclaim-leases parameter limits the number of leases reclaimed in
   a single cycle to 100. The max-reclaim-time limits the maximum duration of
   each cycle to 50ms. The lease reclamation cycle will be interrupted if
   either of these limitations is reached. The reclamation of all unreclaimed
   leases will be attempted in subsequent cycles.

   The following diagram illustrates the behavior of the system in the
   presence of many expired leases, when the limits are applied for the
   reclamation cycles.


 | c1 |                | c2 |                | c3 |                | c4 |
 |<-->|<-------------->|<-->|<-------------->|<-->|<-------------->|<-->|<--
 ------------------------------------------------------------------------------>
 |50ms|       3s       |50ms|       3s       |50ms|       3s       |50ms|  time


   The diagram demonstrates the case when each reclamation cycle would take
   more than 50ms, and thus is interrupted according to the value of the
   max-reclaim-time. This results in equal durations of all reclamation
   cycles over time. Note that in this example the limitation of maximum 100
   leases is not reached. This may be the case when database transactions are
   slow or callouts in the hook libraries attached to the server are slow.
   Regardless, the choosing values for either the maximum number of leases or
   a maximum cycle time strongly depends on the particular deployment, lease
   database backend being used, and any hooks libraries etc. Administrators
   may need to experiment to tune the system to suit the dynamics of their
   deployment.

   It is important to realize that with the use of these limits, there is a
   risk that expired leases will accumulate faster than the server can
   reclaim them. This should not be the problem if the server is dealing with
   a temporary burst of expirations, because it should be able to eventually
   deal with them over time. However, if leases expire at the high rate for a
   longer period of time, the unreclaimed leases will pile up in the
   database. In order to notify the administrator that the current
   configuration does not satisfy the needs for reclamation of expired
   leases, the server issues a warning message in the log, if it was unable
   to reclaim all leases within the last couple of reclamation cycles. The
   number of cycles after which such warning is issued is specified with the
   unwarned-reclaim-cycles configuration parameter.

   Setting the reclaim-timer-wait-time to 0 disables periodic reclamation of
   the expired leases.

9.3. Configuring Lease Affinity

   Suppose that a laptop goes to a sleep mode after a period of user
   inactivity. While the laptop is in sleep mode, its DHCP client will not
   renew leases obtained from the server and these leases will eventually
   expire. When the laptop wakes up, it is often desired that it continue
   using its previous assigned IP addresses. In order to facilitate this, the
   server needs to correlate returning clients with their expired leases When
   the client returns, the server will first check for those leases and
   re-assign them if they have not assigned to another client. The ability of
   the server to re-assign the same lease to a returning client is referred
   to as 'lease affinity'.

   When lease affinity is enabled, the server will still reclaim leases
   according to the parameters described in Section 9.2, "Configuring Leases
   Reclamation", but the reclaimed leases will be held in the database
   (rather than removed) for the specified amount of time. When the client
   returns, the server will first check if there are any reclaimed leases
   associated with this client and re-assign them if possible. However, it is
   important to note that any reclaimed lease may be assigned to another
   client if that client specifically asks for it. Therefore, the lease
   affinity does not guarantee that the reclaimed lease will be available for
   the client who used it before. It merely increases the chances for the
   client to be assigned the same lease. If the lease pool is small (mostly
   applies to DHCPv4 for which address space is small), there is an increased
   likelihood that the expired lease will be hijacked by another client.

   Consider the following configuration:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 3,
         "hold-reclaimed-time": 1800,
         "flush-reclaimed-timer-wait-time": 5
     },

     ...
 }

   The hold-reclaim-time specifies how many seconds after an expiration a
   reclaimed lease should be held in the database for re-assignment to the
   same client. In the example given above, reclaimed leases will be held for
   30 minutes (1800s) after their expiration. During this time, the server
   will likely be able to re-assign the same lease to the returning client,
   unless another client requests this lease and the server assigns it.

   The server must periodically remove reclaimed leases for which the time
   indicated by hold-reclaim-time has elapsed. The
   flush-reclaimed-timer-wait-time controls how often the server removes such
   leases. In the example provided above, the server will initiate removal of
   such leases 5 seconds after the previous removal attempt was completed.
   Setting this value to 0 disables lease affinity, in which case leases will
   be removed from the lease database when they are reclaimed. If lease
   affinity is enabled, it is recommended that hold-reclaim-time be set to a
   value significantly higher than the reclaim-timer-wait-time, as timely
   removal of expired-reclaimed leases is less critical while the removal
   process may impact server responsiveness.

9.4. Default Configuration Values for Leases Reclamation

   The following list presents all configuration parameters pertaining to
   processing expired leases with their default values:

     * reclaim-timer-wait-time = 10 [seconds]
     * flush-reclaimed-timer-wait-time = 25 [seconds]
     * hold-reclaimed-time = 3600 [seconds]
     * max-reclaim-leases = 100
     * max-reclaim-time = 250 [milliseconds]
     * unwarned-reclaim-cycles = 5

   The default value for any parameter is used when this parameter not
   explicitly specified in the configuration. Also, the
   expired-leases-processing map may be omitted entirely in the
   configuration, in which case the default values are used for all
   parameters listed above.

9.5. Reclaiming Expired Leases with Command

   The leases-reclaim command can be used to trigger leases reclamation at
   any time. Please consult the Section 15.3.1, "leases-reclaim command" for
   the details about using this command.

                        Chapter 10. The DHCP-DDNS Server

   Table of Contents

   10.1. Starting and Stopping the DHCP-DDNS Server

   10.2. Configuring the DHCP-DDNS Server

                10.2.1. Global Server Parameters

                10.2.2. TSIG Key List

                10.2.3. Forward DDNS

                10.2.4. Reverse DDNS

                10.2.5. Example DHCP-DDNS Server Configuration

   10.3. DHCP-DDNS Server Limitations

   The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the
   client side of the DDNS protocol (defined in RFC 2136) on behalf of the
   DHCPv4 and DHCPv6 servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP
   servers construct DDNS update requests, known as NameChangeRequests
   (NCRs), based upon DHCP lease change events and then post these to D2. D2
   attempts to match each such request to the appropriate DNS server(s) and
   carry out the necessary conversation with those servers to update the DNS
   data.

   In order to match a request to the appropriate DNS servers, D2 must have a
   catalog of servers from which to select. In fact, D2 has two such
   catalogs, one for forward DNS and one for reverse DNS; these catalogs are
   referred to as DDNS Domain Lists. Each list consists of one or more named
   DDNS Domains. Further, each DDNS Domain has a list of one or more DNS
   servers that publish the DNS data for that domain.

   When conducting forward domain matching, D2 will compare the FQDN in the
   request against the name of each forward DDNS Domain. The domain whose
   name matches the longest portion of the FQDN is considered the best match.
   For example, if the FQDN is "myhost.sample.example.com.", and there are
   two forward domains in the catalog: "sample.example.com." and
   "example.com.", the former is regarded as the best match. In some cases,
   it may not be possible to find a suitable match. Given the same two
   forward domains there would be no match for the FQDN, "bogus.net", so the
   request would be rejected. Finally, if there are no forward DDNS Domains
   defined, D2 will simply disregard the forward update portion of requests.

   When conducting reverse domain matching, D2 constructs a reverse FQDN from
   the lease address in the request and compare that against the name of each
   reverse DDNS Domain. Again, the domain whose name matches the longest
   portion of the FQDN is considered the best match. For instance, if the
   lease address is "172.16.1.40" and there are two reverse domains in the
   catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the former is
   the best match. As with forward matching, it is possible to not find a
   suitable match. Given the same two domains, there would be no match for
   the lease address, "192.168.1.50", and the request would be rejected.
   Finally, if there are no reverse DDNS Domains defined, D2 will simply
   disregard the reverse update portion of requests.

10.1. Starting and Stopping the DHCP-DDNS Server

   kea-dhcp-ddns is the Kea DHCP-DDNS server and, due to the nature of DDNS,
   it is run alongside either the DHCPv4 or DHCPv6 components (or both). Like
   other parts of Kea, it is a separate binary that can be run on its own or
   through keactrl (see Chapter 6, Managing Kea with keactrl). In normal
   operation, controlling kea-dhcp-ddns with keactrl is recommended. However,
   it is also possible to run the DHCP-DDNS server directly. It accepts the
   following command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     * -v - prints out Kea version and exits.
     * -V - prints out Kea extended version with additional parameters and
       exits.
     * -W - prints out Kea configuration report and exits.

   The -V command returns the versions of the external libraries dynamically
   linked.

   The -W command describes the environment used to build Kea. This command
   displays a copy of the config.report file produced by ./configure that is
   embedded in the executable binary.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/d2/.libs/kea-dhcp-ddns.

 strings path/kea-dhcp-ddns | sed -n 's/;;;; //p'

   Upon start up the module will load its configuration and begin listening
   for NCRs based on that configuration.

   During startup the server will attempt to create a PID file of the form:
   [localstatedir]/[conf name].kea-dhcp-ddns.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP_DDNS_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

10.2. Configuring the DHCP-DDNS Server

   Before starting kea-dhcp-ddns module for the first time, a configuration
   file needs to be created. The following default configuration is a
   template that can be customised to your requirements.

 "DhcpDdns": {
     "ip-address": "127.0.0.1",
     "port": 53001,
     "dns-server-timeout": 100,
     "ncr-protocol": "UDP",
     "ncr-format": "JSON",
     "tsig-keys": [ ],
     "forward-ddns": {
         "ddns-domains": [ ]
     },
     "reverse-ddns": {
         "ddns-domains": [ ]
     }
 }

   The configuration can be divided as follows, each of which is described in
   its own section:

     * Global Server Parameters - values which control connectivity and
       global server behavior
     * TSIG Key Info - defines the TSIG keys used for secure traffic with DNS
       servers
     * Forward DDNS - defines the catalog of Forward DDNS Domains
     * Reverse DDNS - defines the catalog of Forward DDNS Domains

  10.2.1. Global Server Parameters

     * ip-address - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * port - Port on which D2 listens for requests. The default value is
       53001.
     * dns-server-timeout - The maximum amount of time in milliseconds, that
       D2 will wait for a response from a DNS server to a single DNS update
       message.
     * ncr-protocol - Socket protocol to use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     * ncr-format - Packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   D2 must listen for change requests on a known address and port. By default
   it listens at 127.0.0.1 on port 53001. The following example illustrates
   how to change D2's global parameters so it will listen at 192.168.1.10
   port 900:

 "DhcpDdns": {
     "ip-address": "192.168.1.10",
     "port": 900,
     ...
     }
 }

  Warning

   It is possible for a malicious attacker to send bogus NameChangeRequests
   to the DHCP-DDNS server. Addresses other than the IPv4 or IPv6 loopback
   addresses (127.0.0.1 or ::1) should only be used for testing purposes, but
   note that local users may still communicate with the DHCP-DDNS server. A
   future version of Kea will implement authentication to guard against such
   attacks.

  Note

   If the ip-address and port are changed, it will be necessary to change the
   corresponding values in the DHCP servers' "dhcp-ddns" configuration
   section.

  10.2.2. TSIG Key List

   A DDNS protocol exchange can be conducted with or without TSIG (defined in
   RFC 2845). This configuration section allows the administrator to define
   the set of TSIG keys that may be used in such exchanges.

   To use TSIG when updating entries in a DNS Domain, a key must be defined
   in the TSIG Key List and referenced by name in that domain's configuration
   entry. When D2 matches a change request to a domain, it checks whether the
   domain has a TSIG key associated with it. If so, D2 will use that key to
   sign DNS update messages sent to and verify responses received from the
   domain's DNS server(s). For each TSIG key required by the DNS servers that
   D2 will be working with there must be a corresponding TSIG key in the TSIG
   Key list.

   As one might gather from the name, the tsig-key section of the D2
   configuration lists the TSIG keys. Each entry describes a TSIG key used by
   one or more DNS servers to authenticate requests and sign responses. Every
   entry in the list has three parameters:

     * name - a unique text label used to identify this key within the list.
       This value is used to specify which key (if any) should be used when
       updating a specific domain. So long as it is unique its content is
       arbitrary, although for clarity and ease of maintenance it is
       recommended that it match the name used on the DNS server(s). It
       cannot be blank.
     * algorithm - specifies which hashing algorithm should be used with this
       key. This value must specify the same algorithm used for the key on
       the DNS server(s). The supported algorithms are listed below:

          * HMAC-MD5
          * HMAC-SHA1
          * HMAC-SHA224
          * HMAC-SHA256
          * HMAC-SHA384
          * HMAC-SHA512

       This value is not case sensitive.
     * digest-bits - is used to specify the minimum truncated length in bits.
       The default value 0 means truncation is forbidden, not 0 values must
       be an integral number of octets, be greater than 80 and the half of
       the full length. Note in BIND9 this parameter is appended after a dash
       to the algorithm name.
     * secret - is used to specify the shared secret key code for this key.
       This value is case sensitive and must exactly match the value
       specified on the DNS server(s). It is a base64-encoded text value.

   As an example, suppose that a domain D2 will be updating is maintained by
   a BIND9 DNS server which requires dynamic updates to be secured with TSIG.
   Suppose further that the entry for the TSIG key in BIND9's named.conf file
   looks like this:

    :
    key "key.four.example.com." {
        algorithm hmac-sha224;
        secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
    };
    :

   By default, the TSIG Key list is empty:

 "DhcpDdns": {
    "tsig-keys": [ ],
    ...
 }

   We must extend the list with a new key:

 "DhcpDdns": {
     "tsig-keys": [
         {
             "name": "key.four.example.com.",
             "algorithm": "HMAC-SHA224",
             "secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
         }
     ],
     ...
 }

   These steps would be repeated for each TSIG key needed. Note that the same
   TSIG key can be used with more than one domain.

  10.2.3. Forward DDNS

   The Forward DDNS section is used to configure D2's forward update
   behavior. Currently it contains a single parameter, the catalog of forward
   DDNS Domains, which is a list of structures.

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [ ]
     },
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   forward update portions of requests.

    10.2.3.1. Adding Forward DDNS Domains

   A forward DDNS Domain maps a forward DNS zone to a set of DNS servers
   which maintain the forward DNS data (i.e. name to address mapping) for
   that zone. You will need one forward DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers. You will still need one DDNS Domain per zone.
   Remember that matching a request to the appropriate server(s) is done by
   zone and a DDNS Domain only defines a single zone.

   This section describes how to add Forward DDNS Domains. Repeat these steps
   for each Forward DDNS Domain desired. Each Forward DDNS Domain has the
   following parameters:

     * name - The fully qualified domain name (or zone) that this DDNS Domain
       can update. This is value used to compare against the request FQDN
       during forward matching. It must be unique within the catalog.
     * key-name - If TSIG is used with this domain's servers, this value
       should be the name of the key from within the TSIG Key List to use. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers.
     * dns-servers - A list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. The servers are used
       in a first to last preference. In other words, when D2 begins to
       process a request for this domain it will pick the first server in
       this list and attempt to communicate with it. If that attempt fails,
       it will move to next one in the list and so on until the it achieves
       success or the list is exhausted.

   To create a new forward DDNS Domain, one must add a new domain element and
   set its parameters:

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "other.example.com.",
                 "key-name": "",
                 "dns-servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      10.2.3.1.1. Adding Forward DNS Servers

   This section describes how to add DNS servers to a Forward DDNS Domain.
   Repeat them for as many servers as desired for a each domain.

   Forward DNS Server entries represent actual DNS servers which support the
   server side of the DDNS protocol. Each Forward DNS Server has the
   following parameters:

     * hostname - The resolvable host name of the DNS server. This value is
       not yet implemented.
     * ip-address - The IP address at which the server listens for DDNS
       requests. This may be either an IPv4 or an IPv6 address.
     * port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new forward DNS Server, one must add a new server element to
   the domain and fill in its parameters. If for example the service is
   running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "other.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     {
                         "hostname": "",
                         "ip-address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip-address" must be set to the address of the DNS server.

  10.2.4. Reverse DDNS

   The Reverse DDNS section is used to configure D2's reverse update
   behavior, and the concepts are the same as for the forward DDNS section.
   Currently it contains a single parameter, the catalog of reverse DDNS
   Domains, which is a list of structures.

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [ ]
     }
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   reverse update portions of requests.

    10.2.4.1. Adding Reverse DDNS Domains

   A reverse DDNS Domain maps a reverse DNS zone to a set of DNS servers
   which maintain the reverse DNS data (address to name mapping) for that
   zone. You will need one reverse DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers; even then, you will still need one DDNS Domain entry
   for each zone. Remember that matching a request to the appropriate
   server(s) is done by zone and a DDNS Domain only defines a single zone.

   This section describes how to add Reverse DDNS Domains. Repeat these steps
   for each Reverse DDNS Domain desired. Each Reverse DDNS Domain has the
   following parameters:

     * name - The fully qualified reverse zone that this DDNS Domain can
       update. This is the value used during reverse matching which will
       compare it with a reversed version of the request's lease address. The
       zone name should follow the appropriate standards: for example, to to
       support the IPv4 subnet 172.16.1, the name should be.
       "1.16.172.in-addr.arpa.". Similarly, to support an IPv6 subnet of
       2001:db8:1, the name should be "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
       Whatever the name, it must be unique within the catalog.
     * key-name - If TSIG should be used with this domain's servers, then
       this value should be the name of that key from the TSIG Key List. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers. Currently this value is not
       used as TSIG has not been implemented.
     * dns-servers - a list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. Currently the
       servers are used in a first to last preference. In other words, when
       D2 begins to process a request for this domain it will pick the first
       server in this list and attempt to communicate with it. If that
       attempt fails, it will move to next one in the list and so on until
       the it achieves success or the list is exhausted.

   To create a new reverse DDNS Domain, one must add a new domain element and
   set its parameters. For example, to support subnet 2001:db8:1::, the
   following configuration could be used:

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      10.2.4.1.1. Adding Reverse DNS Servers

   This section describes how to add DNS servers to a Reverse DDNS Domain.
   Repeat them for as many servers as desired for each domain.

   Reverse DNS Server entries represents a actual DNS servers which support
   the server side of the DDNS protocol. Each Reverse DNS Server has the
   following parameters:

     * hostname - The resolvable host name of the DNS server. This value is
       currently ignored.
     * ip-address - The IP address at which the server listens for DDNS
       requests.
     * port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new reverse DNS Server, one must first add a new server
   element to the domain and fill in its parameters. If for example the
   service is running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     {
                         "hostname": "",
                         "ip-address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip-address" must be set to the address of the DNS server.

  10.2.5. Example DHCP-DDNS Server Configuration

   This section provides an example DHCP-DDNS server configuration based on a
   small example network. Let's suppose our example network has three
   domains, each with their own subnet.

   Table 10.1. Our example network

   +------------------------------------------------------------------------+
   | Domain           | Subnet          | Forward DNS Servers | Reverse DNS |
   |                  |                 |                     | Servers     |
   |------------------+-----------------+---------------------+-------------|
   | four.example.com | 192.0.2.0/24    | 172.16.1.5,         | 172.16.1.5, |
   |                  |                 | 172.16.2.5          | 172.16.2.5  |
   |------------------+-----------------+---------------------+-------------|
   | six.example.com  | 2001:db8:1::/64 | 3001:1::50          | 3001:1::51  |
   |------------------+-----------------+---------------------+-------------|
   | example.com      | 192.0.0.0/16    | 172.16.2.5          | 172.16.2.5  |
   +------------------------------------------------------------------------+

   We need to construct three forward DDNS Domains:

   Table 10.2. Forward DDNS Domains Needed

   +-------------------------------------------------+
   | #  | DDNS Domain Name  | DNS Servers            |
   |----+-------------------+------------------------|
   | 1. | four.example.com. | 172.16.1.5, 172.16.2.5 |
   |----+-------------------+------------------------|
   | 2. | six.example.com.  | 3001:1::50             |
   |----+-------------------+------------------------|
   | 3. | example.com.      | 172.16.2.5             |
   +-------------------------------------------------+

   As discussed earlier, FQDN to domain matching is based on the longest
   match. The FQDN, "myhost.four.example.com.", will match the first domain
   ("four.example.com") while "admin.example.com." will match the third
   domain ("example.com"). The FQDN, "other.example.net." will fail to match
   any domain and would be rejected.

   The following example configuration specified the Forward DDNS Domains.

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "four.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.1.5" },
                     { "ip-address": "172.16.2.5" }
                 ]
             },
             {
                 "name": "six.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "2001:db8::1" }
                 ]
             },
             {
                 "name": "example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.2.5" }
                 ]
             },

         ]
     }
 }

   Similarly, we need to construct the three reverse DDNS Domains:

   Table 10.3. Reverse DDNS Domains Needed

   +-----------------------------------------------------------------+
   | #  | DDNS Domain Name                  | DNS Servers            |
   |----+-----------------------------------+------------------------|
   | 1. | 2.0.192.in-addr.arpa.             | 172.16.1.5, 172.16.2.5 |
   |----+-----------------------------------+------------------------|
   | 2. | 1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa. | 3001:1::50             |
   |----+-----------------------------------+------------------------|
   | 3. | 0.182.in-addr.arpa.               | 172.16.2.5             |
   +-----------------------------------------------------------------+

   An address of "192.0.2.150" will match the first domain, "2001:db8:1::10"
   will match the second domain, and "192.0.50.77" the third domain.

   These Reverse DDNS Domains are specified as follows:

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "2.0.192.in-addr.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.1.5" },
                     { "ip-address": "172.16.2.5" }
                 ]
             }
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "2001:db8::1" }
                 ]
             }
             {
                 "name": "0.192.in-addr.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.2.5" }
                 ]
             }
         ]
     }
 }

10.3. DHCP-DDNS Server Limitations

   The following are the current limitations of the DHCP-DDNS Server.

     * Requests received from the DHCP servers are placed in a queue until
       they are processed. Currently all queued requests are lost when the
       server shuts down.

                          Chapter 11. The LFC process

   Table of Contents

   11.1. Overview

   11.2. Command Line Options

11.1. Overview

   kea-lfc is a service process that removes redundant information from the
   files used to provide persistent storage for the memfile data base
   backend. This service is written to run as a stand alone process.

   While kea-lfc can be started externally, there is usually no need to do
   this. kea-lfc is run on a periodic basis by the Kea DHCP servers.

   The process operates on a set of files, using them for input and output of
   the lease entries and to indicate where it is in the process in case of an
   interruption. Currently the caller must supply names for all of the files,
   in the future this requirement may be relaxed with the process getting the
   names from either the config file or from defaults.

11.2. Command Line Options

   kea-lfc is run as follows:

 kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file

   The argument -4 or -6 selects the protocol version of the lease files.

   The -c argument specifies the configuration file. This is required, but
   not currently used by the process.

   The -p argument specifies the PID file. When the kea-lfc process starts it
   attempts to determine if another instance of the process is already
   running by examining the pid file. If one is already running the new
   process is terminated. If one isn't running it writes its pid into the pid
   file.

   The other filenames specify where the kea-lfc process should look for
   input, write its output and use for bookkeeping.

     * previous -- When kea-lfc starts this is the result of any previous run
       of kea-lfc. When kea-lfc finishes it is the result of this run. If
       kea-lfc is interrupted before completing, this file may not exist.
     * input -- Before the DHCP server invokes kea-lfc it will move the
       current lease file here and then call kea-lfc with this file.
     * output -- The temporary file kea-lfc should use to write the leases.
       Upon completion of writing this file, it will be moved to the finish
       file (see below).
     * finish -- Another temporary file kea-lfc uses for bookkeeping. When
       kea-lfc completes writing the outputfile it moves it to this file
       name. After kea-lfc finishes deleting the other files (previous and
       input) it moves this file to previous lease file. By moving the files
       in this fashion the kea-lfc and the DHCP server processes can
       determine the correct file to use even if one of the processes was
       interrupted before completing its task.

   There are several additional arguments mostly for debugging purposes. -d
   Sets the logging level to debug. -v and -V print out version stamps with
   -V providing a longer form. -h prints out the usage string.

                       Chapter 12. Client Classification

   Table of Contents

   12.1. Client Classification Overview

   12.2. Using Vendor Class Information In Classification

   12.3. Using Expressions In Classification

                12.3.1. Substring

   12.4. Configuring Classes

   12.5. Configuring Subnets With Class Information

   12.6. Using Classes

   12.7. Classes and Hooks

12.1. Client Classification Overview

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. Common reasons include:

     * The clients represent different pieces of topology, e.g. a cable modem
       is different to the clients behind that modem.

     * The clients have different behavior, e.g. a smart phone behaves
       differently to a laptop.

     * The clients require different values for some options, e.g. a
       docsis3.0 cable modem requires different settings to docsis2.0 cable
       modem.

   It is envisaged that client classification will be used for changing the
   behavior of almost any part of the DHCP message processing, including the
   assignment of leases from different pools, the assignment of different
   options (or different values of the same options) etc. In the current
   release of the software however, there are only three mechanisms that take
   advantage of client classification: subnet selection, assignment of
   different options and, for DHCPv4 cable modems, the setting of specific
   options for use with the TFTP server address and the boot file field.

   The process of doing classification is conducted in three steps:

    1. Assess an incoming packet and assign it to zero or more classes.

    2. Choose a subnet, possibly based on the class information.

    3. Assign options, again possibly based on the class information.

   When determining which options to include in the response the server will
   examine the union of options from all of the assigned classes. In the case
   two or more classes include the same option, the value from the first
   class examined will be used. When choosing a subnet the server will
   iterate over all of the subnets that are feasible given the information
   found in the packet (client address, relay address etc). It will use the
   first subnet it finds that either doesn't have a class associated with it
   or that has a class which matches one of the packet's classes. In the
   future the processing order of the various classes may be specified but
   for now it is being left unspecified and may change in future releases.

   As an example, imagine two classes. Class "foo" defines values for an NTP
   server (option 42 in DHCPv4) and an SMTP server (option 69 in DHCPv4)
   while class "bar" defines values for an NTP server and a POP3 server
   (option 70 in DHCPv4). The server will examine the three options NTP, SMTP
   and POP3 and return any of them that the client requested. As the NTP
   server was defined twice the server will choose only one of the values for
   the reply: the class from which the value is obtained is unspecified.

   There are two methods of doing classification. The first is automatic and
   relies on examining the values in the vendor class options. Information
   from these options is extracted and a class name is constructed from it
   and added to the class list for the packet. The second allows you to
   specify an expression that is evaluated for each packet. If the result is
   true, the packet is a member of the class.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

12.2. Using Vendor Class Information In Classification

   The server checks whether an incoming DHCPv4 packet includes the vendor
   class identifier option (60) or an incoming DHCPv6 packet includes the
   vendor class option (16). If it does, the content of that option is
   prepended with "VENDOR_CLASS_" and the result is interpreted as a class.
   For example, modern cable modems will send this option with value
   "docsis3.0" and so the packet will belong to class
   "VENDOR_CLASS_docsis3.0".

12.3. Using Expressions In Classification

   The expression portion of classification contains operators and values.
   All values are currently strings and operators take a string or strings
   and return another string. When all the operations have completed the
   result should be a value of "true" or "false". The packet belongs to the
   class (and the class name is added to the list of classes) if the result
   is "true". Expressions are written in standard format and can be nested.

   Expressions are pre-processed during the parsing of the configuration file
   and converted to an internal representation. This allows certain types of
   errors to be caught and logged during parsing. Examples of these errors
   include incorrect number or types of arguments to an operator. The
   evaluation code will also check for this class of error and generally
   throw an exception, though they should not occur in a normally functioning
   system.

   Other issues, for example the starting position of a substring being
   outside of the substring or an option not existing in the packet, result
   in the operator returning an empty string.

   Expressions are a work in progress and the supported operators and values
   are limited. The expectation is that additional operators and values will
   be added over time, however it is expected the basic mechanisms will
   remain the same.

   Table 12.1. List of Classification Values

   +------------------------------------------------------------------------+
   |    Name    |     Example      |              Description               |
   |------------+------------------+----------------------------------------|
   | String     | 'example'        | A string                               |
   |------------+------------------+----------------------------------------|
   | Hex String | 0XABCD           | A hexadecimal string                   |
   |------------+------------------+----------------------------------------|
   | Integer    | 123              | An integer value                       |
   |------------+------------------+----------------------------------------|
   | Option Hex | option[code].hex | The value of the option with code      |
   |            |                  | "code" from the packet as hex          |
   +------------------------------------------------------------------------+

   Hex Strings are converted into a string as expected. The starting "0X" or
   "0x" is removed and if the string is an odd number of characters a "0" is
   prepended to it.

   Integers in the expression are converted to strings when the expression is
   read into Kea.

   "option[code].hex" extracts the value of the option with the given code
   from the incoming packet. If the packet doesn't contain the option, it
   returns the empty string. The string is presented as a byte string of the
   option payload without the type code or length fields.

   Table 12.2. List of Classification Expressions

   +------------------------------------------------------------------------+
   |   Name    |         Example         |           Description            |
   |-----------+-------------------------+----------------------------------|
   | Equal     | 'foo' == 'bar'          | Compare the two values and       |
   |           |                         | return "true" or "false"         |
   |-----------+-------------------------+----------------------------------|
   | Substring | substring('foobar',0,3) | Return the requested substring   |
   +------------------------------------------------------------------------+

  12.3.1. Substring

   The substring operator "substring(value, start, length)" accepts both
   positive and negative values for the starting position and the length. For
   "start", a value of 0 is the first byte in the string while -1 is the last
   byte. If the starting point is outside of the original string an empty
   string is returned. "length" is the number of bytes to extract. A negative
   number means to count towards the beginning of the string but doesn't
   include the byte pointed to by "start". The special value "all" means to
   return all bytes from start to the end of the string. If length is longer
   than the remaining portion of the string then the entire remaining portion
   is returned. Some examples may be helpful:

         substring('foobar', 0, 6) == 'foobar'
         substring('foobar', 3, 3) == 'bar'
         substring('foobar', 3, all) == 'bar'
         substring('foobar', 1, 4) == 'ooba'
         substring('foobar', -5, 4) == 'ooba'
         substring('foobar', -1, -3) == 'oba'
         substring('foobar', 4, -2) == 'ob'
         substring('foobar', 10, 2) == ''


  Note

   The expression for each class is executed on each packet received. If the
   expressions are overly complex, the time taken to execute them may impact
   the performance of the server. If you need complex or time consuming
   expressions you should write a hook to perform the necessary work.

12.4. Configuring Classes

   A class contains three items: a name, a test expression and option data.
   The name must exist and must be unique amongst all classes. The test
   expression and option data are optional.

   The test expression is a string containing the logical expression used to
   determine membership in the class. The entire expression is in double
   quotes.

   The option data is a list which defines any options that should be
   assigned to members of this class.

   In the following example the class named "Client_foo" is defined. It is
   comprised of all clients who's client ids (option 61) start with the
   string "foo". Members of this class will be given 192.0.2.1 and 192.0.2.2
   as their domain name servers.

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     ...
 }

   This example shows a client class being defined for use by the DHCPv6
   server. In it the class named "Client_enterprise" is defined. It is
   comprised of all clients who's client identifiers start with the given hex
   string (which would indicate a DUID based on an enterprise id of
   0xAABBCCDD). Members of this class will be given an 2001:db8:0::1 and
   2001:db8:2::1 as their domain name servers.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     ...
 }

12.5. Configuring Subnets With Class Information

   In certain cases it beneficial to restrict access to certain subnets only
   to clients that belong to a given class using the "client-class" keyword
   when defining the subnet.

   Let's assume that the server is connected to a network segment that uses
   the 192.0.2.0/24 prefix. The Administrator of that network has decided
   that addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed
   by the DHCP4 server. Only clients belonging to client class Client_foo are
   allowed to use this subnet. Such a configuration can be achieved in the
   following way:

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "Client_foo"
         },
         ...
     ],,
     ...
 }

   The following example shows restricting access to a DHCPv6 subnet. This
   configuration will restrict use of the addresses 2001:db8:1::1 to
   2001:db8:1::FFFF to members of the "Client_enterprise" class.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
             "client-class": "Client_enterprise"
         }
     ],
     ...
 }

12.6. Using Classes

   Currently classes can be used for two functions. They can supply options
   to the members of the class and they can be used to choose a subnet from
   which an address will be assigned to the class member.

   When supplying options, options defined as part of the class definition
   are considered "class globals". They will override any global options that
   may be defined and in turn will be overridden by any options defined for
   an individual subnet.

12.7. Classes and Hooks

   You may use a hook to classify your packets. This may be useful if the
   expression would either be complex or time consuming and be easier or
   better to write as code. Once the hook has added the proper class name to
   the packet the rest of the classification system will work as normal in
   choosing a subnet and selecting options. For a description of the hooks
   see Chapter 13, Hooks Libraries, for a description on configuring he
   classes see Section 12.4, "Configuring Classes" and Section 12.5,
   "Configuring Subnets With Class Information".

                          Chapter 13. Hooks Libraries

   Table of Contents

   13.1. Introduction

   13.2. Configuring Hooks Libraries

13.1. Introduction

   Although Kea offers a lot of flexibility, there may be cases where its
   behavior needs customisation. To accommodate this possibility, Kea
   includes the idea of "Hooks". This feature lets Kea load one or more
   dynamically-linked libraries (known as "hooks libraries") and, at various
   points in its processing ("hook points"), call functions in them. Those
   functions perform whatever custom processing is required.

   Hooks libraries are attached to individual Kea processes, not to Kea as a
   whole. This means (for example) that it is possible to associate one set
   of libraries with the DHCP4 server and a different set to the DHCP6
   server.

   Another point to note is that it is possible for a process to load
   multiple libraries. When processing reaches a hook point, Kea calls the
   hooks library functions attached to it. If multiple libraries have
   attached a function to a given hook point, Kea calls all of them, in the
   order in which the libraries are specified in the configuration file. The
   order may be important: consult the documentation of the libraries to see
   if this is the case.

   The next section describes how to configure hooks libraries. If you are
   interested in writing your own hooks library, information can be found in
   the Kea Developer's Guide.

13.2. Configuring Hooks Libraries

   The hooks libraries for a given process are configured using the
   hooks-libraries keyword in the configuration for that process. (Note that
   the word "hooks" is plural). The value of the keyword is an array of map
   structures, each structure corresponding to a hooks library. For example,
   to set up two hooks libraries for the DHCPv4 server, the configuration
   would be:

 "Dhcp4": {
     :
     "hooks-libraries": [
         {
             "library": "/opt/charging.so"
         },
         {
             "library": "/opt/local/notification.so"
         }
     ]
     :
 }

  Note

   This is a change to the syntax used in Kea 0.9.2 and earlier, where
   hooks-libraries was a list of strings, each string being the name of a
   library. The change has been made in Kea 1.0 to facilitate the
   specification of library-specific parameters, a feature that will be added
   to a future version of Kea.

   Notes:

     * The full path to each library should be given.

     * As noted above, order may be important - consult the documentation for
       each library.

     * An empty list has the same effect as omitting the hooks-libraries
       configuration element all together.

  Note

       There is one case where this is not true: if Kea is running with a
       configuration that contains a hooks-libraries item, and that item is
       removed and the configuration reloaded, the removal will be ignored
       and the libraries remain loaded. As a workaround, instead of removing
       the hooks-libraries item, change it to an empty list. This will be
       fixed in a future version of Kea.

   At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
   hooks libraries.

                             Chapter 14. Statistics

   Table of Contents

   14.1. Statistics Overview

   14.2. Statistics Lifecycle

   14.3. Commands for Manipulating Statistics

                14.3.1. statistic-get command

                14.3.2. statistic-reset command

                14.3.3. statistic-remove command

                14.3.4. statistic-get-all command

                14.3.5. statistic-reset-all command

                14.3.6. statistic-remove-all command

14.1. Statistics Overview

   Both Kea DHCP servers support statistics gathering since 0.9.2-beta
   version. A working DHCP server encounters various events that can cause
   certain statistics to be collected. For example, a DHCPv4 server may
   receive a packet (pkt4-received statistic increases by one) that after
   parsing was identifier as DHCPDISCOVER (pkt4-discover-received). The
   Server processed it and decided to send DHCPOFFER representing its answer
   (pkt4-offer-sent and pkt4-sent statistics increase by one). Such events
   happen frequently, so it is not uncommon for the statistics to have values
   in high thousands. They can serve as an easy and powerful tool for
   observing a server's and network's health. For example, if pkt4-received
   statistic stops growing, it means that the clients' packets are not
   reaching the server.

   There are four types of statistics:

     * integer - this is the most common type. It is implemented as 64 bit
       integer (int64_t in C++), so it can hold any value between -2^63 to
       2^63 -1.
     * floating point - this type is intended to store floating point
       precision. It is implemented as double C++ type.
     * duration - this type is intended for recording time periods. It uses
       boost::posix_time::time_duration type, which stores hours, minutes,
       seconds and microseconds.
     * string - this type is intended for recording statistics in textual
       form. It uses std::string C++ type.

   During normal operation, DHCPv4 and DHCPv6 servers gather statistics. For
   a list of DHCPv4 and DHCPv6 statistics, see Section 7.7, "Statistics in
   DHCPv4 server" and Section 8.11, "Statistics in DHCPv6 server",
   respectively.

   To extract data from the statistics module, the control channel can be
   used. See Chapter 15, Management API for details. It is possible to
   retrieve a single or all statistics, reset statistics (i.e. set to neutral
   value, typically zero) or even remove completely a single or all
   statistics. See section Section 14.3, "Commands for Manipulating
   Statistics" for a list of statistic oriented commands.

14.2. Statistics Lifecycle

   It is useful to understand how the Statistics Manager module works. When
   the server starts operation, the manager is empty and does not have any
   statistics. When statistic-get-all is executed, an empty list is returned.
   Once the server performs an operation that causes a statistic to change,
   the related statistic will be created. In the general case once a
   statistic is recorded even once, it is kept in the manager, until
   explicitly removed, by statistic-remove or statistic-remove-all being
   called or the server is shut down. Per subnet statistics are explicitly
   removed when reconfiguration takes place.

   Statistics are considered run-time properties, so they are not retained
   after server restart.

   Removing a statistic that is updated frequently makes little sense as it
   will be re-added when the server code next records that statistic. The
   statistic-remove and statistic-remove-all commands are intended to remove
   statistics that are not expected to be observed in the near future. For
   example, a misconfigured device in a network may cause clients to report
   duplicate addresses, so the server will report increasing values of
   pkt4-decline-received. Once the problem is found and the device is
   removed, the system administrator may want to remove the
   pkt4-decline-received statistic, so it won't be reported anymore. If a
   duplicate address is detected ever again, the server will add this
   statistic back.

14.3. Commands for Manipulating Statistics

   There are several commands defined that can be used for accessing (-get),
   resetting to zero or neutral value (-reset) or even removing a statistic
   completely (-remove). The difference between reset and remove is somewhat
   subtle. The reset command sets the value of the statistic to zero or
   neutral value. After this operation, the statistic will have a value of 0
   (integer), 0.0 (float), 0h0m0s0us (duration) or "" (string). When asked
   for, a statistic with the values mentioned will be returned. Remove
   removes a statistic completely, so the statistic will not be reported
   anymore. Please note that the server code may add it back if there's a
   reason to record it.

  14.3.1. statistic-get command

   statistic-get command retrieves a single statistic. It takes a single
   string parameter called name that specifies the statistic name. An example
   command may look like this:

 {
     "command": "statistic-get",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   The server will respond with details of the requested statistic, with
   result set to 0 indicating success and the specified statistic as the
   value of "arguments" parameter. If the requested statistic is not found,
   the response will contain an empty map, i.e. only { } as argument, but the
   status code will still be set to success (0).

  14.3.2. statistic-reset command

   statistic-reset command sets the specified statistic to its neutral value:
   0 for integer, 0.0 for float, 0h0m0s0us for time duration and "" for
   string type. It takes a single string parameter called name that specifies
   the statistic name. An example command may look like this:

 {
     "command": "statistic-reset",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and reset was successful, the server
   will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

  14.3.3. statistic-remove command

   statistic-remove command attempts to delete a single statistic. It takes a
   single string parameter called name that specifies the statistic name. An
   example command may look like this:

 {
     "command": "statistic-remove",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and its removal was successful, the
   server will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

  14.3.4. statistic-get-all command

   statistic-get-all command retrieves all statistics recorded. An example
   command may look like this:

 {
     "command": "statistic-get-all",
     "arguments": { }
 }

   The server will respond with details of all recorded statistics, with
   result set to 0 indicating that it iterated over all statistics (even when
   the total number of statistics is zero).

  14.3.5. statistic-reset-all command

   statistic-reset command sets all statistics to their neutral values: 0 for
   integer, 0.0 for float, 0h0m0s0us for time duration and "" for string
   type. An example command may look like this:

 {
     "command": "statistic-reset-all",
     "arguments": { }
 }

   If the operation is successful, the server will respond with a status of
   0, indicating success and an empty parameters field. If an error is
   encountered, the server will return a status code of 1 (error) and the
   text field will contain the error description.

  14.3.6. statistic-remove-all command

   statistic-remove-all command attempts to delete all statistics. An example
   command may look like this:

 {
     "command": "statistic-remove-all",
     "arguments": { }
 }

   If the removal of all statistics was successful, the server will respond
   with a status of 0, indicating success and an empty parameters field. If
   an error is encountered, the server will return a status code of 1 (error)
   and the text field will contain the error description.

                           Chapter 15. Management API

   Table of Contents

   15.1. Data syntax

   15.2. Using control channel

   15.3. Commands supported by both DHCPv4 and DHCPv6 servers

                15.3.1. leases-reclaim command

                15.3.2. list-commands command

                15.3.3. shutdown command

   A classic approach to daemon configuration assumes that the server's
   configuration is stored in the configuration files and when the
   configuration is changed, the daemon is restarted. This approach has the
   significant disadvantage of introducing periods of downtime, when client
   traffic is not handled. Another risk is that if the new configuration is
   invalid for whatever reason, the server may refuse to start, which will
   further extend the downtime period, until the issue is resolved.

   To avoid such problems, both DHCPv4 and DHCPv6 servers introduced support
   for a mechanism that will allow on-line reconfiguration, without requiring
   server shutdown. Both servers can be instructed to open control sockets,
   which is a communication channel. The server is able to receive commands
   on that channel, act on them and report back status. While the set of
   commands supported in Kea 0.9.2 is limited, the number is expected to grow
   over time.

   Currently the only supported type of control channel is UNIX stream
   socket. For details how to configure it, see Section 7.8, "Management API
   for the DHCPv4 server" and Section 8.12, "Management API for the DHCPv6
   server". It is likely that support for other control channel types will be
   added in the future.

15.1. Data syntax

   Communication over control channel is conducted using JSON structures. If
   configured, Kea will open a socket and will listen for any incoming
   connections. A process connecting to this socket is expected to send JSON
   commands structured as follows:

 {
     "command": "foo",
     "arguments": {
         "param1": "value1",
         "param2": "value2",
         ...
     }
 }

   command is the name of command to execute and is mandatory. arguments is a
   map of parameters required to carry out the given command. The exact
   content and format is command specific.

   The server will process the incoming command and then send a response of
   the form:

 {
     "result": 0|1,
     "text": "textual description",
     "arguments": {
         "argument1": "value1",
         "argument2": "value2",
         ...
     }
 }

   result indicates the outcome of the command. A value of 0 means success
   while any non-zero value designates an error. Currently 1 is used as a
   generic error, but additional error codes may be added in the future. text
   field typically appears when result is non-zero and contains a description
   of the error encountered, but it may also appear for successful results.
   That's command specific. arguments is a map of additional data values
   returned by the server, specific to the command issued. The map is always
   present, even if it contains no data values.

15.2. Using control channel

   ISC does not provide a client for using control channel. The primary
   reason for that is the expectation is that the entity using control
   channel is typically an IPAM or similar network management/monitoring
   software which may have quite varied expectations regarding the client and
   is even likely to be written in languages different than C or C++.
   Therefore we only provide examples how one can take advantage of the API.

   The easiest way is to use a tool called socat, a tool available from socat
   homepage, but it is also widely available in Linux and BSD distributions.
   Once Kea is started, one could connect to the control interface using the
   following command:

 $ socat UNIX:/path/to/the/kea/socket -

   where /path/to/the/kea/socket is the path specified in the
   Dhcp4/control-socket/socket-name parameter in the Kea configuration file.

   It is also easy to open UNIX socket programmatically. An example of such a
   simplistic client written in C is available in the Kea Developer's Guide,
   chapter Control Channel Overview, section Using Control Channel.

15.3. Commands supported by both DHCPv4 and DHCPv6 servers

  15.3.1. leases-reclaim command

   leases-reclaim command instructs the server to reclaim all expired leases
   immediately. The command has the following JSON syntax:

 {
     "command": "leases-reclaim",
     "arguments": {
         "remove": true
     }
 }

   The remove boolean parameter is mandatory and it indicates whether the
   reclaimed leases should be removed from the lease database (if true), or
   they should be left in the expired-reclaimed state (if false). The latter
   facilitates lease affinity, i.e. ability to re-assign expired lease to the
   same client which used this lease before. See Section 9.3, "Configuring
   Lease Affinity" for the details. Also, see Section 9.1, "Lease
   Reclamation" for the general information about the processing of expired
   leases (leases reclamation).

  15.3.2. list-commands command

   list-commands command retrieves a list of all commands supported by the
   server. It does not take any arguments. An example command may look like
   this:

 {
     "command": "list-commands",
     "arguments": { }
 }

   The server will respond with a list of all supported commands. The
   arguments element will be a list of strings. Each string will convey one
   supported command.

  15.3.3. shutdown command

   shutdown command instructs the server to initiate its shutdown procedure.
   It is the equivalent of sending a SIGTERM signal to the process. This
   command does not take any arguments. An example command may look like
   this:

 {
     "command": "shutdown",
     "arguments": { }
 }

   The server will respond with a confirmation that the shutdown procedure
   has been initiated.

                         Chapter 16. libdhcp++ library

   Table of Contents

   16.1. Interface detection and Socket handling

   libdhcp++ is a common library written in C++ that handles many
   DHCP-related tasks, including:

     * DHCPv4 and DHCPv6 packets parsing, manipulation and assembly
     * Option parsing, manipulation and assembly
     * Network interface detection
     * Socket operations such as creation, data transmission and reception
       and socket closing.

   While this library is currently used by Kea, it is designed to be a
   portable, universal library, useful for any kind of DHCP-related software.

16.1. Interface detection and Socket handling

   Both the DHCPv4 and DHCPv6 components share network interface detection
   routines. Interface detection is currently supported on Linux, all BSD
   family (FreeBSD, NetBSD, OpenBSD), Mac OS X and Solaris 11 systems.

   DHCPv4 requires special raw socket processing to send and receive packets
   from hosts that do not have IPv4 address assigned yet. Support for this
   operation is implemented on Linux, FreeBSD, NetBSD and OpenBSD. It is
   likely that DHCPv4 component will not work in certain cases on other
   systems.

                              Chapter 17. Logging

   Table of Contents

   17.1. Logging Configuration

                17.1.1. Loggers

                17.1.2. Output Options

                17.1.3. Example Logger Configurations

   17.2. Logging Message Format

   17.3. Logging During Kea Startup

17.1. Logging Configuration

   During its operation Kea may produce many messages. They differ in
   severity (some are more important than others) and source (some are
   produced by specific components, e.g. hooks). It is useful to understand
   which log messages are needed and which are not and configure your logging
   appropriately. For example, debug level messages can be safely ignored in
   a typical deployment. They are, however, very useful when debugging a
   problem.

   The logging system in Kea is configured through the Logging structure in
   your configuration file. All daemons (e.g. DHCPv4 and DHCPv6 servers) will
   use the configuration in the Logging structure to see what should be
   logged and to where. This allows for sharing identical logging
   configuration between daemons.

  17.1.1. Loggers

   Within Kea, a message is logged through an entity called a "logger".
   Different components log messages through different loggers, and each
   logger can be configured independently of one another. Some components, in
   particular the DHCP server processes, may use multiple loggers to log
   messages pertaining to different logical functions of the component. For
   example, the DHCPv4 server is using one logger for messages pertaining to
   packet reception and transmission, another logger for messages related to
   lease allocation and so on. Some of the libraries used by the Kea servers,
   e.g. libdhcpsrv or libhooks library, use their own loggers.

   Users implementing hooks libraries (code attached to the server at
   runtime) are responsible for creating the loggers used by those libraries.
   Such loggers should have unique names, different from the logger names
   used by Kea. In this way the messages emitted from the hooks library can
   be distingued from messages issued by the core Kea code. Unique names also
   allow the loggers to be configured independently of loggers used by Kea.
   Whenever it makes sense, a hook library can use multiple loggers to log
   messages pertaining to different logical parts of the library.

   In the "Logging" structure of a configuration file you can specify the
   configuration for zero or more loggers (including loggers used by the
   proprietary hooks libraries). If there are no loggers specified, the code
   will use default values which cause Kea to log messages on at least INFO
   severity to standard output.

   The three most important elements of a logger configuration are the name
   (the component that is generating the messages), the severity (what to
   log), and the output_options (where to log).

    17.1.1.1. name (string)

   Each logger in the system has a name, the name being that of the component
   binary file using it to log messages. For instance, if you want to
   configure logging for the DHCPv4 server, you add an entry for a logger
   named "kea-dhcp4". This configuration will then be used by the loggers in
   the DHCPv4 server, and all the libraries used by it (unless a library
   defines its own logger and there is specific logger configuration that
   applies to that logger).

   When diagnosing the problem with the server's operation, it is often
   desired to use the DEBUG logging level to obtain the verbose output from
   the server and libraries it uses. However, high verbosity may be an
   overkill for the logging system in cases when the server is processing
   high volume traffic. To mitigate this problem, Kea is using multiple
   loggers, which can be configured independently and which are responsible
   for logging messages from different functional parts of the server. If the
   user, trying to diagnose the problem, has a reasonably high confidence
   that the problem origins in a specific function of the server, or the
   problem is related to the specific type of operation, he may enable high
   verbosity only for the relevant logger, thus limiting the debug messages
   to the required minimum.

   The loggers are associated with a particular library or binary of Kea.
   However, each library or binary may (and usually does) include multiple
   loggers. For example, the DHCPv4 server binary contains separate loggers
   for: packet parsing, for dropped packets, for callouts etc. Each logger
   "derives" its configuration from the root logger. In the typical case, the
   root logger configuration is the only logging configuration specified in
   the configuration file. Creating a specific configuration for the selected
   logger, thus overriding the configuration settings specified in the root
   logger configuration, requires putting its configuration aside of the root
   logger's configuration with some of the parameters modified.

   To illustrate this, suppose you are using the DHCPv4 server with the root
   logger "kea-dhcp4" logging at the INFO level. In order to enable DEBUG
   verbosity for the DHCPv4 packet drops, you must create configuration entry
   for the logger called "kea-dhcp4.bad-packets" and specify severity DEBUG
   for this logger. All other configuration parameters may be omited for this
   logger if the logger should use the default values specified in the root
   logger's configuration.

   If there are multiple logger specifications in the configuration that
   might match a particular logger, the specification with the more specific
   logger name takes precedence. For example, if there are entries for both
   "kea-dhcp4" and "kea-dhcp4.dhcpsrv", the DHCPv4 server -- and all
   libraries it uses that are not dhcpsrv -- will log messages according to
   the configuration in the first entry ("kea-dhcp4").

   Currently defined loggers are:

     * kea-dhcp4 - this is the root logger for the DHCPv4 server. All
       components used by the DHCPv4 server inherit the settings from this
       logger if there is no specialized logger provided.
     * kea-dhcp4.alloc-engine - this is the logger used by the lease
       allocation engine, which is responsible for managing leases in the
       lease database, i.e. create, modify and remove DHCPv4 leases as a
       result of processing messages from the clients.
     * kea-dhcp4.bad-packets - this is the logger used by the DHCPv4 server
       daemon for logging inbound client packets that were dropped or to
       which the server responded with a DHCPNAK. The allows administrators
       to configure a separate log output that contains only packet drop and
       reject entries.
     * kea-dhcp4.callouts - this logger is used to log messages pertaining to
       the callouts registration and execution for the particular hook point.
     * kea-dhcp4.commands - this logger is used to log messages relating to
       the handling of commands received by the the DHCPv4 server over the
       command channel.
     * kea-dhcp4.ddns - this logger is used by the DHCPv4 server to log
       messages related to the Client FQDN and Hostname option processing. It
       also includes log messages related to the relevant DNS updates.
     * kea-dhcp4.dhcp4 - this is the logger by the DHCPv4 server daemon to
       log basic operations.
     * kea-dhcp4.dhcpsrv - this is a base logger for the libdhcpsrv library.
     * kea-dhcp4.eval - this logger is used to log messages relating to the
       client classification expression evaluation code.
     * kea-dhcp4.hooks - this logger is used to log messages related to
       management of hooks libraries, e.g. registration and deregistration of
       the libraries, and to the initialization of the callouts execution for
       various hook points within the DHCPv4 server.
     * kea-dhcp4.hosts - this logger is used within the libdhcpsrv and it
       logs messages related to the management of the DHCPv4 host
       reservations, i.e. retrieval of the reservations and adding new
       reservations.
     * kea-dhcp4.leases - this logger is used by the DHCPv4 server to log
       messages related to the lease allocation. The messages include
       detailed information about the allocated or offered leases, errors
       during the lease allocation etc.
     * kea-dhcp4.options - this logger is used by the DHCPv4 server to log
       messages related to processing of the options in the DHCPv4 messages,
       i.e. parsing options, encoding options into on-wire format and packet
       classification using options contained in the received packets.
     * kea-dhcp4.packets - this logger is mostly used to log messages related
       to transmission of the DHCPv4 packets, i.e. packet reception and
       sending a response. Such messages include the information about the
       source and destination IP addresses and interfaces used to transmit
       packets. This logger is also used to log messages related to subnet
       selection, as this selection is usually based on the IP addresses
       and/or interface names, which can be retrieved from the received
       packet, even before the DHCPv4 message carried in the packet is
       parsed.
     * kea-dhcp6 - this is the root logger for the DHCPv6 server. All
       components used by the DHCPv6 server inherit the settings from this
       logger if there is no specialized logger provided.
     * kea-dhcp6.alloc-engine - this is the logger used by the lease
       allocation engine, which is responsible for managing leases in the
       lease database, i.e. create, modify and remove DHCPv6 leases as a
       result of processing messages from the clients.
     * kea-dhcp6.bad-packets - this is the logger used by the DHCPv6 server
       daemon for logging inbound client packets that were dropped.
     * kea-dhcp6.callouts - this logger is used to log messages pertaining to
       the callouts registration and execution for the particular hook point.
     * kea-dhcp6.commands - this logger is used to log messages relating to
       the handling of commands received by the the DHCPv6 server over the
       command channel.
     * kea-dhcp6.ddns - this logger is used by the DHCPv6 server to log
       messages related to the Client FQDN option processing. It also
       includes log messages related to the relevant DNS updates.
     * kea-dhcp6.dhcp6 - this is the logger used DHCPv6 server daemon to log
       basic operations.
     * kea-dhcp6.dhcpsrv - this is a base logger for the libdhcpsrv library.
     * kea-dhcp6.eval - this logger is used to log messages relating to the
       client classification expression evaluation code.
     * kea-dhcp6.hooks - this logger is used to log messages related to
       management of hooks libraries, e.g. registration and deregistration of
       the libraries, and to the initialization of the callouts execution for
       various hook points within the DHCPv6 server.
     * kea-dhcp6.hosts - this logger is used within the libdhcpsrv and it
       logs messages related to the management of the DHCPv6 host
       reservations, i.e. retrieval of the reservations and adding new
       reservations.
     * kea-dhcp6.leases - this logger is used by the DHCPv6 server to log
       messages related to the lease allocation. The messages include
       detailed information about the allocated or offered leases, errors
       during the lease allocation etc.
     * kea-dhcp6.options - this logger is used by the DHCPv6 server to log
       messages related to processing of the options in the DHCPv6 messages,
       i.e. parsing options, encoding options into on-wire format and packet
       classification using options contained in the received packets.
     * kea-dhcp6.packets - this logger is mostly used to log messages related
       to transmission of the DHCPv6 packets, i.e. packet reception and
       sending a response. Such messages include the information about the
       source and destination IP addresses and interfaces used to transmit
       packets. This logger is also used to log messages related to subnet
       selection, as this selection is usually based on the IP addresses
       and/or interface names, which can be retrieved from the received
       packet, even before the DHCPv6 message carried in the packet is
       parsed.
     * kea-dhcp-ddns - this is the root logger for the kea-dhcp-ddns daemon.
       All components used by this daemon inherit the settings from this
       logger if there is no specialized logger provided.
     * kea-dhcp-ddns.dhcpddns - this is the logger used by the kea-dhcp-ddns
       daemon for logging configuration and global event information. This
       logger does not specify logging settings for libraries used by the
       daemon.
     * kea-dhcp-ddns.dhcp-to-d2 - this is the logger used by the
       kea-dhcp-ddns daemon for logging information about events dealing with
       receiving messages from the DHCP servers and adding them to the queue
       for processing.
     * kea-dhcp-ddns.d2-to-dns - this is the logger used by the kea-dhcp-ddns
       daemon for logging information about events dealing with sending and
       receiving messages with the DNS servers.

   Note that user-defined hook libraries should not use any of those loggers,
   and should define new loggers with names that correspond to the libraries
   using them. Suppose that the user created the library called
   "libpacket-capture" to dump packets received and transmitted by the server
   to the file. The appropriate name for the logger could be
   kea-dhcp4.packet-capture. Note that the hook library implementor only
   specifies the second part of this name, i.e. "packet-capture". The first
   part is a root logger name and is prepended by the Kea logging system. It
   is also important to note that since this new logger is a child of a root
   logger, it inherits the configuration from the root logger, unless there
   is a separate configuration entry for the child logger which overrides the
   default configuration.

   The list of loggers above excludes any loggers implemented in hooks
   libraries. Please consult the documentation of the specific hooks
   libraries for the names of loggers they define.

   Additional loggers may be defined in the future. The easiest way to find
   out the logger name is to configure all logging to go to a single
   destination and look for specific logger names. See Section 17.2, "Logging
   Message Format" for details.

    17.1.1.2. severity (string)

   This specifies the category of messages logged. Each message is logged
   with an associated severity which may be one of the following (in
   descending order of severity):

     * FATAL
     * ERROR
     * WARN
     * INFO
     * DEBUG

   When the severity of a logger is set to one of these values, it will only
   log messages of that severity, and the severities above it. The severity
   may also be set to NONE, in which case all messages from that logger are
   inhibited.

    17.1.1.3. output_options (list)

   Each logger can have zero or more output_options. These specify where log
   messages are sent. These are explained in detail below.

   The other options for a logger are:

    17.1.1.4. debuglevel (integer)

   When a logger's severity is set to DEBUG, this value specifies what debug
   messages should be printed. It ranges from 0 (least verbose) to 99 (most
   verbose).

   If severity for the logger is not DEBUG, this value is ignored.

  17.1.2. Output Options

   The main settings for an output option are the destination and a value
   called output, the meaning of which depends on the destination that is
   set.

    17.1.2.1. destination (string)

   The destination is the type of output. It can be one of:

     * console
     * file
     * syslog

    17.1.2.2. output (string)

   This value determines the type of output. There are several special values
   allowed here: stdout (messages are printed on standard output), stderr
   (messages are printed on stderr), syslog (messages are logged to syslog
   using default name, syslog:name (messages are logged to syslog using
   specified name). Any other value is interpreted as a filename that the
   logs should be written to.

   The other options for output_options are:

      17.1.2.2.1. flush (true of false)

   Flush buffers after each log message. Doing this will reduce performance
   but will ensure that if the program terminates abnormally, all messages up
   to the point of termination are output. Default is true.

      17.1.2.2.2. maxsize (integer)

   Only relevant when destination is file, this is maximum file size of
   output files in bytes. When the maximum size is reached, the file is
   renamed and a new file opened. (For example, a ".1" is appended to the
   name -- if a ".1" file exists, it is renamed ".2", etc.)

   If this is 0, no maximum file size is used.

  Note

   Due to a limitation of the underlying logging library (log4cplus), rolling
   over the log files (from ".1" to ".2", etc) may show odd results: There
   can be multiple small files at the timing of roll over. This can happen
   when multiple processes try to roll over the files simultaneously. Version
   1.1.0 of log4cplus solved this problem, so if this or higher version of
   log4cplus is used to build Kea, it shouldn't happen. Even for older
   versions it is normally expected to happen rarely unless the log messages
   are produced very frequently by multiple different processes.

      17.1.2.2.3. maxver (integer)

   Maximum number of old log files to keep around when rolling the output
   file. Only relevant when output is "file".

  17.1.3. Example Logger Configurations

   In this example we want to set the global logging to write to the console
   using standard output.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp4",
             "output_options": [
                 {
                     "output": "stdout"
                 }
             ],
             "severity": "WARN"
         }
     ]
 }


   In this second example, we want to store debug log messages in a file that
   is at most 2MB and keep up to 8 copies of old logfiles. Once the logfile
   grows to 2MB, it will be renamed and a new file file be created.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp6",
             "output_options": [
                 {
                     "output": "/var/log/kea-debug.log",
                     "maxver": 8,
                     "maxsize": 204800,
                     "flush": true
                 }
             ],
             "severity": "DEBUG",
             "debuglevel": 99
         }
    ]
 }

17.2. Logging Message Format

   Each message written to the configured logging destinations comprises a
   number of components that identify the origin of the message and, if the
   message indicates a problem, information about the problem that may be
   useful in fixing it.

   Consider the message below logged to a file:

 2014-04-11 12:58:01.005 INFO  [kea-dhcp4.dhcpsrv/27456]
     DHCPSRV_MEMFILE_DB opening memory file lease database: type=memfile universe=4

   Note: the layout of messages written to the system logging file (syslog)
   may be slightly different. This message has been split across two lines
   here for display reasons; in the logging file, it will appear on one line.

   The log message comprises a number of components:

   2014-04-11 12:58:01.005

           The date and time at which the message was generated.

   INFO

           The severity of the message.

   [kea-dhcp4.dhcpsrv/27456]

           The source of the message. This comprises two elements: the Kea
           process generating the message (in this case, kea-dhcp4) and the
           component within the program from which the message originated
           (which is the name of the common library used by DHCP server
           implementations). The number after the slash is a process id
           (pid).

   DHCPSRV_MEMFILE_DB

           The message identification. Every message in Kea has a unique
           identification, which can be used as an index into the Kea
           Messages Manual (http://kea.isc.org/docs/kea-messages.html) from
           which more information can be obtained.

   opening memory file lease database: type=memfile universe=4

           A brief description. Within this text, information relating to the
           condition that caused the message to be logged will be included.
           In this example, the information is logged that the in-memory
           lease database backend will be used to store DHCP leases.

17.3. Logging During Kea Startup

   The logging configuration is specified in the configuration file. However,
   when Kea starts, the file is not read until some way into the
   initialization process. Prior to that, the logging settings are set to
   default values, although it is possible to modify some aspects of the
   settings by means of environment variables. Note that in the absence of
   any logging configuration in the configuration file, the settings of
   (possibly modified) default configuration will persist while the program
   is running.

   The following environment variables can be used to control the behavior of
   logging during startup:

   KEA_LOCKFILE_DIR

           Specifies a directory where the logging system should create its
           lock file. If not specified, it is prefix/var/run/kea, where
           prefix defaults to /usr/local. This variable must not end with a
           slash. There is one special value: "none", which instructs Kea to
           not create lock file at all. This may cause issues if several
           processes log to the same file.

   KEA_LOGGER_DESTINATION

           Specifies logging output. There are several special values.

                stdout

                        Log to standard output.

                stderr

                        Log to standard error.

                syslog[:fac]

                        Log via syslog. The optional fac (which is separated
                        from the word "syslog" by a colon) specifies the
                        facility to be used for the log messages. Unless
                        specified, messages will be logged using the facility
                        "local0".

           Any other value is treated as a name of the output file. If not
           specified otherwise, Kea will log to standard output.

                     Chapter 18. Frequently Asked Questions

   Table of Contents

   18.1. Generic Frequently Asked Questions

                18.1.1. Where did the Kea name came from?

                18.1.2. Feature X is not supported yet. When/if will it be
                available?

   18.2. Frequently Asked Questions about DHCPv4

                18.2.1. I set up a firewall, but the Kea server still
                receives the traffic. Why?

   18.3. Frequently Asked Questions about DHCPv6

                18.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I
                checked with tcpdump (or other traffic capture software) that
                the incoming traffic is reaching the box. What's wrong?

   This chapter contains a number of frequently asked questions and
   troubleshooting tips. It currently lacks content, but it is expected to
   grow over time.

18.1. Generic Frequently Asked Questions

  18.1.1. Where did the Kea name came from?

   Kea is the name of a high mountain parrot living in New Zealand. See this
   https://lists.isc.org/pipermail/kea-users/2014-October/000032.html for an
   extended answer.

  18.1.2. Feature X is not supported yet. When/if will it be available?

   Kea is developed by a small team of engineers. Our resources are limited,
   so we need to prioritize requests. The complexity of a new feature (how
   difficult it is to implement a feature and how likely it would break
   something that already works), amount of work required and expected
   popularity (i.e., how many users would actually benefit from it) are three
   leading factors. We sometimes also have contractual obligations.

   Simply stating that you'd like feature X is useful. We try to implement
   features that are actively requested first, but the reality is that we
   have more requests than we can handle, so some of them must be postponed,
   at least in the near future. So is your request likely to be rejected? Not
   at all. You can do many things to greatly improve the chances of your
   request being fulfilled. First, it helps to explain why you need a
   feature. If your explanation is reasonable and there are likely other
   users that would benefit from it, the chances for Kea developers to put
   this task on a roadmap is better. Saying that you are willing to
   participate in tests (e.g., test engineering drops when they become
   available) is also helpful.

   Another thing you can do to greatly improve the chances of a feature to
   appear is to actually develop it on your own and submit a patch. That's an
   avenue that people often forget about. Kea is open source software and we
   do accept patches. There are certain requirements, like code quality,
   comments, unit-tests, documentation, etc., but we have accepted a
   significant number of patches in the past, so it's doable. Accepted
   contributions range from minor documentation corrections to significant
   new features, like support for a new database type. Before considering
   writing and submitting a patch, make sure you read the Contributor's Guide
   in Kea Developer's Guide.

   Kea is developed by ISC, which is a non-profit organization. You may
   consider signing a development contract with us. In the past we did
   implement certain features due to contractual obligations. With additional
   funds we are able to put extra engineering efforts into Kea development.
   We can reshuffle our schedule or add extra hands to the team if needed.
   Please keep in mind that Kea is open source software and its principle
   goal is to provide a good DHCP solution that can be used by everyone. In
   other words, we may refuse a contract that would tie the solution to
   specific proprietary technology or make it unusable for other users. Also,
   we strive to make Kea a reference implementation, so if your proposal
   significantly violates a RFC, we may have a problem with that.
   Nevertheless, please talk to us and we may be able to find a solution.

   Finally, Kea has a public roadmap, with releases happening several times
   each year. We tend to not modify plans for the current milestone, unless
   there are very good reasons to do so. Therefore "I'd like a feature X in 6
   months" is much better received than "I'd like a feature X now".

18.2. Frequently Asked Questions about DHCPv4

  18.2.1. I set up a firewall, but the Kea server still receives the traffic.
  Why?

   Any DHCPv4 server must be able to receive from and send traffic to hosts
   that don't have an IPv4 address assigned yet. That is typically not
   possible with regular UDP sockets, therefore the Kea DHCPv4 server uses
   raw sockets by default. Raw sockets mean that the incoming packets are
   received as raw Ethernet frames, thus bypassing the whole kernel IP stack,
   including any firewalling rules your kernel may provide.

   If you do not want the server to use raw sockets, it is possible to
   configure the Kea DHCPv4 server to use UDP sockets instead. See
   dhcp-socket-type described in Section 7.2.4, "Interface configuration".
   However, using UDP sockets has certain limitations. In particular, they
   may not allow for sending responses directly to clients without IPv4
   addresses assigned. That's ok, if all your traffic is coming through relay
   agents.

18.3. Frequently Asked Questions about DHCPv6

  18.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I checked with
  tcpdump (or other traffic capture software) that the incoming traffic is
  reaching the box. What's wrong?

   Please check whether your OS has any IPv6 filtering rules. Many operating
   systems are shipped with firewalls that discard incoming IPv6 traffic by
   default. In particular, many Linux distributions do that. Please check the
   output of the following command:

 # ip6tables -L -n

   One common mistake in this area is to use iptables tool, which lists IPv4
   firewall rules only.

                          Chapter 19. Acknowledgments

   Kea is primarily designed, developed, and maintained by Internet Systems
   Consortium, Inc. It is an open source project and contributions are
   welcomed.

   Support for the development of the DHCPv4, DHCPv6 and DHCP-DDNS components
   was provided by Comcast.

   Kea was initially implemented as a collection of applications within the
   BIND 10 framework. Hence, Kea development would not be possible without
   the generous support of past BIND 10 project sponsors.

   JPRS and CIRA were Patron Level BIND 10 sponsors.

   AFNIC, CNNIC, CZ.NIC, DENIC eG, Google, RIPE NCC, Registro.br, .nz
   Registry Services, and Technical Center of Internet were past BIND 10
   sponsors.

   Afilias, IIS.SE, Nominet, and SIDN were founding sponsors of the BIND 10
   project.
