dhcpd-options(5)                                              dhcpd-options(5)



[1mNAME[0m
       dhcp-options - Dynamic Host Configuration Protocol options

[1mDESCRIPTION[0m
       The Dynamic Host Configuration protocol allows the client to receive
       [1moptions [22mfrom the DHCP server describing the network configuration and
       various services that are available on the network.   When configuring
       [1mdhcpd(8) [22mor [1mdhclient(8) , [22moptions must often be declared.   The syntax
       for declaring options, and the names and formats of the options that
       can be declared, are documented here.

[1mREFERENCE: OPTION STATEMENTS[0m
       DHCP [4moption[24m statements always start with the [4moption[24m keyword, followed
       by an option name, followed by option data.  The option names and data
       formats are described below.   It is not necessary to exhaustively
       specify all DHCP options - only those options which are needed by
       clients must be specified.

       Option data comes in a variety of formats, as defined below:

       The [1mip-address [22mdata type can be entered either as an explicit IP
       address (e.g., 239.254.197.10) or as a domain name (e.g.,
       haagen.isc.org).  When entering a domain name, be sure that that domain
       name resolves to a single IP address.

       The [1mint32 [22mdata type specifies a signed 32-bit integer.   The [1muint32[0m
       data type specifies an unsigned 32-bit integer.   The [1mint16 [22mand [1muint16[0m
       data types specify signed and unsigned 16-bit integers.   The [1mint8 [22mand
       [1muint8 [22mdata types specify signed and unsigned 8-bit integers.  Unsigned
       8-bit integers are also sometimes referred to as octets.

       The [1mtext [22mdata type specifies an NVT ASCII string, which must be
       enclosed in double quotes - for example, to specify a root-path option,
       the syntax would be

       option root-path "10.0.1.4:/var/tmp/rootfs";

       The [1mdomain-name [22mdata type specifies a domain name, which must not
       enclosed in double quotes.   This data type is not used for any
       existing DHCP options.   The domain name is stored just as if it were a
       text option.

       The [1mdomain-list [22mdata type specifies a list of domain names, a space
       between each name and the entire string enclosed in double quotes.
       These types of data are used for the domain-search option for example,
       and encodes an RFC1035 compressed DNS label list on the wire.

       The [1mflag [22mdata type specifies a boolean value.   Booleans can be either
       true or false (or on or off, if that makes more sense to you).

       The [1mstring [22mdata type specifies either an NVT ASCII string enclosed in
       double quotes, or a series of octets specified in hexadecimal,
       separated by colons.   For example:

         option dhcp-client-identifier "CLIENT-FOO";
       or
         option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f;

[1mSETTING OPTION VALUES USING EXPRESSIONS[0m
       Sometimes it's helpful to be able to set the value of a DHCP option
       based on some value that the client has sent.   To do this, you can use
       expression evaluation.   The [1mdhcp-eval(5) [22mmanual page describes how to
       write expressions.   To assign the result of an evaluation to an
       option, define the option as follows:

         [1moption [4m[22mmy-option[24m [1m= [4m[22mexpression[24m [1m;[0m

       For example:

         option hostname = binary-to-ascii (16, 8, "-",
                                            substring (hardware, 1, 6));

[1mSTANDARD DHCP OPTIONS[0m
       The documentation for the various options mentioned below is taken from
       the latest IETF draft document on DHCP options.  Options not listed
       below may not yet be implemented, but it is possible to use such
       options by defining them in the configuration file.  Please see the
       DEFINING NEW OPTIONS heading later in this document for more
       information.

       Some of the options documented here are automatically generated by the
       DHCP server or by clients, and cannot be configured by the user.  The
       value of such an option can be used in the configuration file of the
       receiving DHCP protocol agent (server or client), for example in
       conditional expressions. However, the value of the option cannot be
       used in the configuration file of the sending agent, because the value
       is determined only [4mafter[24m the configuration file has been processed. In
       the following documentation, such options will be shown as "not user
       configurable"

       The standard options are:

       [1moption all-subnets-local [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client may assume that all
         subnets of the IP network to which the client is connected use the
         same MTU as the subnet of that network to which the client is
         directly connected.  A value of true indicates that all subnets share
         the same MTU.  A value of false means that the client should assume
         that some subnets of the directly connected network may have smaller
         MTUs.

       [1moption arp-cache-timeout [4m[22muint32[24m[1m;[0m

         This option specifies the timeout in seconds for ARP cache entries.

       [1moption bcms-controller-address [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         This option configures a list of IPv4 addresses for use as Broadcast
         and Multicast Controller Servers ("BCMS").

       [1moption bootfile-name [4m[22mtext[24m[1m;[0m

         This option is used to identify a bootstrap file.  If supported by
         the client, it should have the same effect as the [1mfilename[0m
         declaration.  BOOTP clients are unlikely to support this option.
         Some DHCP clients will support it, and others actually require it.

       [1moption boot-size [4m[22muint16[24m[1m;[0m

         This option specifies the length in 512-octet blocks of the default
         boot image for the client.

       [1moption broadcast-address [4m[22mip-address[24m[1m;[0m

         This option specifies the broadcast address in use on the client's
         subnet.  Legal values for broadcast addresses are specified in
         section 3.2.1.3 of STD 3 (RFC1122).

       [1moption cookie-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The cookie server option specifies a list of RFC 865 cookie servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption default-ip-ttl [4m[22muint8;[0m

         This option specifies the default time-to-live that the client should
         use on outgoing datagrams.

       [1moption default-tcp-ttl [4m[22muint8[24m[1m;[0m

         This option specifies the default TTL that the client should use when
         sending TCP segments.  The minimum value is 1.

       [1moption default-url [4m[22mstring[24m[1m;[0m

         The format and meaning of this option is not described in any
         standards document, but is claimed to be in use by Apple Computer.
         It is not known what clients may reasonably do if supplied with this
         option.  Use at your own risk.

       [1moption dhcp-client-identifier [4m[22mstring[24m[1m;[0m

         This option can be used to specify a DHCP client identifier in a host
         declaration, so that dhcpd can find the host record by matching
         against the client identifier.

         Please be aware that some DHCP clients, when configured with client
         identifiers that are ASCII text, will prepend a zero to the ASCII
         text.   So you may need to write:

              option dhcp-client-identifier "\0foo";

         rather than:

              option dhcp-client-identifier "foo";

       [1moption dhcp-lease-time [4m[22muint32[24m[1m;[0m

         This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
         to allow the client to request a lease time for the IP address.  In a
         server reply (DHCPOFFER), a DHCP server uses this option to specify
         the lease time it is willing to offer.

         This option is not directly user configurable in the server; refer to
         the [4mmax-lease-time[24m and [4mdefault-lease-time[24m server options in
         [1mdhcpd.conf(5).[0m

       [1moption dhcp-max-message-size [4m[22muint16[24m[1m;[0m

         This option, when sent by the client, specifies the maximum size of
         any response that the server sends to the client.   When specified on
         the server, if the client did not send a dhcp-max-message-size
         option, the size specified on the server is used.   This works for
         BOOTP as well as DHCP responses.

       [1moption dhcp-message [4m[22mtext[24m[1m;[0m

         This option is used by a DHCP server to provide an error message to a
         DHCP client in a DHCPNAK message in the event of a failure. A client
         may use this option in a DHCPDECLINE message to indicate why the
         client declined the offered parameters.

         This option is not user configurable.

       [1moption dhcp-message-type [4m[22muint8[24m[1m;[0m

         This option, sent by both client and server, specifies the type of
         DHCP message contained in the DHCP packet. Possible values (taken
         directly from RFC2132) are:

                      1     DHCPDISCOVER
                      2     DHCPOFFER
                      3     DHCPREQUEST
                      4     DHCPDECLINE
                      5     DHCPACK
                      6     DHCPNAK
                      7     DHCPRELEASE
                      8     DHCPINFORM

         This option is not user configurable.

       [1moption dhcp-option-overload [4m[22muint8[24m[1m;[0m

         This option is used to indicate that the DHCP 'sname' or 'file'
         fields are being overloaded by using them to carry DHCP options. A
         DHCP server inserts this option if the returned parameters will
         exceed the usual space allotted for options.

         If this option is present, the client interprets the specified
         additional fields after it concludes interpretation of the standard
         option fields.

         Legal values for this option are:

                      1     the 'file' field is used to hold options
                      2     the 'sname' field is used to hold options
                      3     both fields are used to hold options

         This option is not user configurable.

       [1moption dhcp-parameter-request-list [4m[22muint16[24m[1m;[0m

         This option, when sent by the client, specifies which options the
         client wishes the server to return.   Normally, in the ISC DHCP
         client, this is done using the [4mrequest[24m statement.   If this option is
         not specified by the client, the DHCP server will normally return
         every option that is valid in scope and that fits into the reply.
         When this option is specified on the server, the server returns the
         specified options.   This can be used to force a client to take
         options that it hasn't requested, and it can also be used to tailor
         the response of the DHCP server for clients that may need a more
         limited set of options than those the server would normally return.

       [1moption dhcp-rebinding-time [4m[22muint32[24m[1m;[0m

         This option specifies the number of seconds from the time a client
         gets an address until the client transitions to the REBINDING state.

         This option is not user configurable.

       [1moption dhcp-renewal-time [4m[22muint32[24m[1m;[0m

         This option specifies the number of seconds from the time a client
         gets an address until the client transitions to the RENEWING state.

         This option is not user configurable.

       [1moption dhcp-requested-address [4m[22mip-address[24m[1m;[0m

         This option is used by the client in a DHCPDISCOVER to request that a
         particular IP address be assigned.

         This option is not user configurable.

       [1moption dhcp-server-identifier [4m[22mip-address[24m[1m;[0m

         This option is used in DHCPOFFER and DHCPREQUEST messages, and may
         optionally be included in the DHCPACK and DHCPNAK messages.  DHCP
         servers include this option in the DHCPOFFER in order to allow the
         client to distinguish between lease offers.  DHCP clients use the
         contents of the 'server identifier' field as the destination address
         for any DHCP messages unicast to the DHCP server.  DHCP clients also
         indicate which of several lease offers is being accepted by including
         this option in a DHCPREQUEST message.

         The value of this option is the IP address of the server.

         This option is not directly user configurable. See the [4mserver-[0m
         [4midentifier[24m server option in [4mdhcpd.conf(5).[0m

       [1moption domain-name [4m[22mtext[24m[1m;[0m

         This option specifies the domain name that client should use when
         resolving hostnames via the Domain Name System.

       [1moption domain-name-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The domain-name-servers option specifies a list of Domain Name System
         (STD 13, RFC 1035) name servers available to the client.  Servers
         should be listed in order of preference.

       [1moption domain-search [4m[22mdomain-list[24m[1m;[0m

         The domain-search option specifies a 'search list' of Domain Names to
         be used by the client to locate not-fully-qualified domain names.
         The difference between this option and historic use of the domain-
         name option for the same ends is that this option is encoded in
         RFC1035 compressed labels on the wire.  For example:

           option domain-search "example.com", "sales.example.com",
                                "eng.example.com";

       [1moption extensions-path [4m[22mtext[24m[1m;[0m

         This option specifies the name of a file containing additional
         options to be interpreted according to the DHCP option format as
         specified in RFC2132.

       [1moption finger-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The Finger server option specifies a list of Finger servers available
         to the client.  Servers should be listed in order of preference.

       [1moption font-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         This option specifies a list of X Window System Font servers
         available to the client. Servers should be listed in order of
         preference.

       [1moption host-name [4m[22mstring[24m[1m;[0m

         This option specifies the name of the client.  The name may or may
         not be qualified with the local domain name (it is preferable to use
         the domain-name option to specify the domain name).  See RFC 1035 for
         character set restrictions.  This option is only honored by [1mdhclient-[0m
         [1mscript(8) [22mif the hostname for the client machine is not set.

       [1moption ieee802-3-encapsulation [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should use Ethernet
         Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the
         interface is an Ethernet.  A value of false indicates that the client
         should use RFC 894 encapsulation.  A value of true means that the
         client should use RFC 1042 encapsulation.

       [1moption ien116-name-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ];

         The ien116-name-servers option specifies a list of IEN 116 name
         servers available to the client.  Servers should be listed in order
         of preference.

       [1moption impress-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The impress-server option specifies a list of Imagen Impress servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption interface-mtu [4m[22muint16[24m[1m;[0m

         This option specifies the MTU to use on this interface.   The minimum
         legal value for the MTU is 68.

       [1moption ip-forwarding [4m[22mflag[24m[1m;[0m

         This option specifies whether the client should configure its IP
         layer for packet forwarding.  A value of false means disable IP
         forwarding, and a value of true means enable IP forwarding.

       [1moption irc-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The IRC server option specifies a list of IRC servers available to
         the client.  Servers should be listed in order of preference.

       [1moption log-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The log-server option specifies a list of MIT-LCS UDP log servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption lpr-servers [4m[22mip-address[24m  [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The LPR server option specifies a list of RFC 1179 line printer
         servers available to the client.  Servers should be listed in order
         of preference.

       [1moption mask-supplier [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should respond to
         subnet mask requests using ICMP.  A value of false indicates that the
         client should not respond.  A value of true means that the client
         should respond.

       [1moption max-dgram-reassembly [4m[22muint16[24m[1m;[0m

         This option specifies the maximum size datagram that the client
         should be prepared to reassemble.  The minimum legal value is 576.

       [1moption merit-dump [4m[22mtext[24m[1m;[0m

         This option specifies the path-name of a file to which the client's
         core image should be dumped in the event the client crashes.  The
         path is formatted as a character string consisting of characters from
         the NVT ASCII character set.

       [1moption mobile-ip-home-agent [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         This option specifies a list of IP addresses indicating mobile IP
         home agents available to the client.  Agents should be listed in
         order of preference, although normally there will be only one such
         agent.

       [1moption nds-context [4m[22mstring[24m[1m;[0m

         The nds-context option specifies the name of the initial Netware
         Directory Service for an NDS client.

       [1moption nds-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The nds-servers option specifies a list of IP addresses of NDS
         servers.

       [1moption nds-tree-name [4m[22mstring[24m[1m;[0m

         The nds-tree-name option specifies NDS tree name that the NDS client
         should use.

       [1moption netbios-dd-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The NetBIOS datagram distribution server (NBDD) option specifies a
         list of RFC 1001/1002 NBDD servers listed in order of preference.

       [1moption netbios-name-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...][1m;[0m

         The NetBIOS name server (NBNS) option specifies a list of RFC
         1001/1002 NBNS name servers listed in order of preference.   NetBIOS
         Name Service is currently more commonly referred to as WINS.   WINS
         servers can be specified using the netbios-name-servers option.

       [1moption netbios-node-type [4m[22muint8[24m[1m;[0m

         The NetBIOS node type option allows NetBIOS over TCP/IP clients which
         are configurable to be configured as described in RFC 1001/1002.  The
         value is specified as a single octet which identifies the client
         type.

         Possible node types are:

         [4m1[24m    B-node: Broadcast - no WINS

         [4m2[24m    P-node: Peer - WINS only

         [4m4[24m    M-node: Mixed - broadcast, then WINS

         [4m8[24m    H-node: Hybrid - WINS, then broadcast

       [1moption netbios-scope [4m[22mstring[24m[1m;[0m

         The NetBIOS scope option specifies the NetBIOS over TCP/IP scope
         parameter for the client as specified in RFC 1001/1002. See RFC1001,
         RFC1002, and RFC1035 for character-set restrictions.

       [1moption netinfo-server-address [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The [1mnetinfo-server-address [22moption has not been described in any RFC,
         but has been allocated (and is claimed to be in use) by Apple
         Computers.  It's hard to say if the above is the correct format, or
         what clients might be expected to do if values were configured.  Use
         at your own risk.

       [1moption netinfo-server-tag [4m[22mtext[24m[1m;[0m

         The [1mnetinfo-server-tag [22moption has not been described in any RFC, but
         has been allocated (and is claimed to be in use) by Apple Computers.
         It's hard to say if the above is the correct format, or what clients
         might be expected to do if values were configured.  Use at your own
         risk.

       [1moption nis-domain [4m[22mtext[24m[1m;[0m

         This option specifies the name of the client's NIS (Sun Network
         Information Services) domain.  The domain is formatted as a character
         string consisting of characters from the NVT ASCII character set.

       [1moption nis-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         This option specifies a list of IP addresses indicating NIS servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption nisplus-domain [4m[22mtext[24m[1m;[0m

         This option specifies the name of the client's NIS+ domain.  The
         domain is formatted as a character string consisting of characters
         from the NVT ASCII character set.

       [1moption nisplus-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         This option specifies a list of IP addresses indicating NIS+ servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption nntp-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The NNTP server option specifies a list of NNTP servesr available to
         the client.  Servers should be listed in order of preference.

       [1moption non-local-source-routing [4m[22mflag[24m[1m;[0m

         This option specifies whether the client should configure its IP
         layer to allow forwarding of datagrams with non-local source routes
         (see Section 3.3.5 of [4] for a discussion of this topic).  A value
         of false means disallow forwarding of such datagrams, and a value of
         true means allow forwarding.

       [1moption ntp-servers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         This option specifies a list of IP addresses indicating NTP (RFC
         1035) servers available to the client.  Servers should be listed in
         order of preference.

       [1moption nwip-domain [4m[22mstring[24m[1m;[0m

         The name of the NetWare/IP domain that a NetWare/IP client should
         use.

       [1moption nwip-suboptions [4m[22mstring[24m[1m;[0m

         A sequence of suboptions for NetWare/IP clients - see RFC2242 for
         details.   Normally this option is set by specifying specific
         NetWare/IP suboptions - see the NETWARE/IP SUBOPTIONS section for
         more information.

       [1moption path-mtu-aging-timeout [4m[22muint32[24m[1m;[0m

         This option specifies the timeout (in seconds) to use when aging Path
         MTU values discovered by the mechanism defined in RFC 1191.

       [1moption path-mtu-plateau-table [4m[22muint16[24m [[1m, [4m[22muint16[24m...  ][1m;[0m

         This option specifies a table of MTU sizes to use when performing
         Path MTU Discovery as defined in RFC 1191.  The table is formatted as
         a list of 16-bit unsigned integers, ordered from smallest to largest.
         The minimum MTU value cannot be smaller than 68.

       [1moption perform-mask-discovery [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should perform subnet
         mask discovery using ICMP.  A value of false indicates that the
         client should not perform mask discovery.  A value of true means that
         the client should perform mask discovery.

       [1moption policy-filter [4m[22mip-address[24m [4mip-address[0m
                         [[1m, [4m[22mip-address[24m [4mip-address[24m...][1m;[0m

         This option specifies policy filters for non-local source routing.
         The filters consist of a list of IP addresses and masks which specify
         destination/mask pairs with which to filter incoming source routes.

         Any source routed datagram whose next-hop address does not match one
         of the filters should be discarded by the client.

         See STD 3 (RFC1122) for further information.

       [1moption pop-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The POP3 server option specifies a list of POP3 servers available to
         the client.  Servers should be listed in order of preference.

       [1moption resource-location-servers [4m[22mip-address[0m
                                     [[1m, [4m[22mip-address[24m...][1m;[0m

         This option specifies a list of RFC 887 Resource Location servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption root-path [4m[22mtext[24m[1m;[0m

         This option specifies the path-name that contains the client's root
         disk.  The path is formatted as a character string consisting of
         characters from the NVT ASCII character set.

       [1moption router-discovery [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should solicit
         routers using the Router Discovery mechanism defined in RFC 1256.  A
         value of false indicates that the client should not perform router
         discovery.  A value of true means that the client should perform
         router discovery.

       [1moption router-solicitation-address [4m[22mip-address[24m[1m;[0m

         This option specifies the address to which the client should transmit
         router solicitation requests.

       [1moption routers [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         The routers option specifies a list of IP addresses for routers on
         the client's subnet.  Routers should be listed in order of
         preference.

       [1moption slp-directory-agent [4m[22mboolean[24m [4mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         This option specifies two things: the IP addresses of one or more
         Service Location Protocol Directory Agents, and whether the use of
         these addresses is mandatory.   If the initial boolean value is true,
         the SLP agent should just use the IP addresses given.   If the value
         is false, the SLP agent may additionally do active or passive
         multicast discovery of SLP agents (see RFC2165 for details).

         Please note that in this option and the slp-service-scope option, the
         term "SLP Agent" is being used to refer to a Service Location
         Protocol agent running on a machine that is being configured using
         the DHCP protocol.

         Also, please be aware that some companies may refer to SLP as NDS.
         If you have an NDS directory agent whose address you need to
         configure, the slp-directory-agent option should work.

       [1moption slp-service-scope [4m[22mboolean[24m [4mtext[24m[1m;[0m

         The Service Location Protocol Service Scope Option specifies two
         things: a list of service scopes for SLP, and whether the use of this
         list is mandatory.  If the initial boolean value is true, the SLP
         agent should only use the list of scopes provided in this option;
         otherwise, it may use its own static configuration in preference to
         the list provided in this option.

         The text string should be a comma-separated list of scopes that the
         SLP agent should use.   It may be omitted, in which case the SLP
         Agent will use the aggregated list of scopes of all directory agents
         known to the SLP agent.

       [1moption smtp-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The SMTP server option specifies a list of SMTP servers available to
         the client.  Servers should be listed in order of preference.

       [1moption static-routes [4m[22mip-address[24m [4mip-address[0m
                         [[1m, [4m[22mip-address[24m [4mip-address[24m...][1m;[0m

         This option specifies a list of static routes that the client should
         install in its routing cache.  If multiple routes to the same
         destination are specified, they are listed in descending order of
         priority.

         The routes consist of a list of IP address pairs.  The first address
         is the destination address, and the second address is the router for
         the destination.

         The default route (0.0.0.0) is an illegal destination for a static
         route.  To specify the default route, use the [1mrouters [22moption.   Also,
         please note that this option is not intended for classless IP routing
         - it does not include a subnet mask.   Since classless IP routing is
         now the most widely deployed routing standard, this option is
         virtually useless, and is not implemented by any of the popular DHCP
         clients, for example the Microsoft DHCP client.

       [1moption streettalk-directory-assistance-server [4m[22mip-address[0m
                                                  [[1m, [4m[22mip-address[24m...][1m;[0m

         The StreetTalk Directory Assistance (STDA) server option specifies a
         list of STDA servers available to the client.  Servers should be
         listed in order of preference.

       [1moption streettalk-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The StreetTalk server option specifies a list of StreetTalk servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption subnet-mask [4m[22mip-address[24m[1m;[0m

         The subnet mask option specifies the client's subnet mask as per RFC
         950.  If no subnet mask option is provided anywhere in scope, as a
         last resort dhcpd will use the subnet mask from the subnet
         declaration for the network on which an address is being assigned.
         However, [4many[24m subnet-mask option declaration that is in scope for the
         address being assigned will override the subnet mask specified in the
         subnet declaration.

       [1moption subnet-selection [4m[22mstring[24m[1m;[0m

         Sent by the client if an address is required in a subnet other than
         the one that would normally be selected (based on the relaying
         address of the connected subnet the request is obtained from). See
         RFC3011. Note that the option number used by this server is 118; this
         has not always been the defined number, and some clients may use a
         different value. Use of this option should be regarded as slightly
         experimental!

       This option is not user configurable in the server.

       [1moption swap-server [4m[22mip-address[24m[1m;[0m

         This specifies the IP address of the client's swap server.

       [1moption tcp-keepalive-garbage [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should send TCP
         keepalive messages with an octet of garbage for compatibility with
         older implementations.  A value of false indicates that a garbage
         octet should not be sent. A value of true indicates that a garbage
         octet should be sent.

       [1moption tcp-keepalive-interval [4m[22muint32[24m[1m;[0m

         This option specifies the interval (in seconds) that the client TCP
         should wait before sending a keepalive message on a TCP connection.
         The time is specified as a 32-bit unsigned integer.  A value of zero
         indicates that the client should not generate keepalive messages on
         connections unless specifically requested by an application.

       [1moption tftp-server-name [4m[22mtext[24m[1m;[0m

         This option is used to identify a TFTP server and, if supported by
         the client, should have the same effect as the [1mserver-name[0m
         declaration.   BOOTP clients are unlikely to support this option.
         Some DHCP clients will support it, and others actually require it.

       [1moption time-offset [4m[22mint32[24m[1m;[0m

         The time-offset option specifies the offset of the client's subnet in
         seconds from Coordinated Universal Time (UTC).

       [1moption time-servers [4m[22mip-address[24m [, [4mip-address[24m...  ][1m;[0m

         The time-server option specifies a list of RFC 868 time servers
         available to the client.  Servers should be listed in order of
         preference.

       [1moption trailer-encapsulation [4m[22mflag[24m[1m;[0m

         This option specifies whether or not the client should negotiate the
         use of trailers (RFC 893 [14]) when using the ARP protocol.  A value
         of false indicates that the client should not attempt to use
         trailers.  A value of true means that the client should attempt to
         use trailers.

       [1moption uap-servers [4m[22mtext[24m[1m;[0m

         This option specifies a list of URLs, each pointing to a user
         authentication service that is capable of processing authentication
         requests encapsulated in the User Authentication Protocol (UAP).  UAP
         servers can accept either HTTP 1.1 or SSLv3 connections.  If the list
         includes a URL that does not contain a port component, the normal
         default port is assumed (i.e., port 80 for http and port 443 for
         https).  If the list includes a URL that does not contain a path
         component, the path /uap is assumed.   If more than one URL is
         specified in this list, the URLs are separated by spaces.

       [1moption user-class [4m[22mstring[24m[1m;[0m

         This option is used by some DHCP clients as a way for users to
         specify identifying information to the client.   This can be used in
         a similar way to the vendor-class-identifier option, but the value of
         the option is specified by the user, not the vendor.   Most recent
         DHCP clients have a way in the user interface to specify the value
         for this identifier, usually as a text string.

       [1moption vendor-class-identifier [4m[22mstring[24m[1m;[0m

         This option is used by some DHCP clients to identify the vendor type
         and possibly the configuration of a DHCP client.  The information is
         a string of bytes whose contents are specific to the vendor and are
         not specified in a standard.   To see what vendor class identifier
         clients are sending, you can write the following in your DHCP server
         configuration file:

         set vendor-string = option vendor-class-identifier;

         This will result in all entries in the DHCP server lease database
         file for clients that sent vendor-class-identifier options having a
         set statement that looks something like this:

         set vendor-string = "SUNW.Ultra-5_10";

         The vendor-class-identifier option is normally used by the DHCP
         server to determine the options that are returned in the [1mvendor-[0m
         [1mencapsulated-options [22moption.   Please see the VENDOR ENCAPSULATED
         OPTIONS section later in this manual page for further information.

       [1moption vendor-encapsulated-options [4m[22mstring[24m[1m;[0m

         The [1mvendor-encapsulated-options [22moption can contain either a single
         vendor-specific value or one or more vendor-specific suboptions.
         This option is not normally specified in the DHCP server
         configuration file - instead, a vendor class is defined for each
         vendor, vendor class suboptions are defined, values for those
         suboptions are defined, and the DHCP server makes up a response on
         that basis.

         Some default behaviours for well-known DHCP client vendors
         (currently, the Microsoft Windows 2000 DHCP client) are configured
         automatically, but otherwise this must be configured manually - see
         the VENDOR ENCAPSULATED OPTIONS section later in this manual page for
         details.

       [1moption www-server [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         The WWW server option specifies a list of WWW servers available to
         the client.  Servers should be listed in order of preference.

       [1moption x-display-manager [4m[22mip-address[24m [[1m, [4m[22mip-address[24m...  ][1m;[0m

         This option specifies a list of systems that are running the X Window
         System Display Manager and are available to the client.  Addresses
         should be listed in order of preference.

[1mRELAY AGENT INFORMATION OPTION[0m
       An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
       encapsulated options that a relay agent can add to a DHCP packet when
       relaying it to the DHCP server.   The server can then make address
       allocation decisions (or whatever other decisions it wants) based on
       these options.   The server also returns these options in any replies
       it sends through the relay agent, so that the relay agent can use the
       information in these options for delivery or accounting purposes.

       The current draft defines two options.   To reference these options in
       the dhcp server, specify the option space name, "agent", followed by a
       period, followed by the option name.   It is not normally useful to
       define values for these options in the server, although it is
       permissible.   These options are not supported in the client.

       [1moption agent.circuit-id [4m[22mstring[24m[1m;[0m

         The circuit-id suboption encodes an agent-local identifier of the
         circuit from which a DHCP client-to-server packet was received.  It
         is intended for use by agents in relaying DHCP responses back to the
         proper circuit.   The format of this option is currently defined to
         be vendor-dependent, and will probably remain that way, although the
         current draft allows for for the possibility of standardizing the
         format in the future.

       [1moption agent.remote-id [4m[22mstring[24m[1m;[0m

         The remote-id suboption encodes information about the remote host end
         of a circuit.   Examples of what it might contain include caller ID
         information, username information, remote ATM address, cable modem
         ID, and similar things.   In principal, the meaning is not well-
         specified, and it should generally be assumed to be an opaque object
         that is administratively guaranteed to be unique to a particular
         remote end of a circuit.

       [1moption agent.DOCSIS-device-class [4m[22muint32[24m[1m;[0m

         The DOCSIS-device-class suboption is intended to convey information
         about the host endpoint, hardware, and software, that either the host
         operating system or the DHCP server may not otherwise be aware of
         (but the relay is able to distinguish).  This is implemented as a
         32-bit field (4 octets), each bit representing a flag describing the
         host in one of these ways.  So far, only bit zero (being the least
         significant bit) is defined in RFC3256.  If this bit is set to one,
         the host is considered a CPE Controlled Cable Modem (CCCM).  All
         other bits are reserved.

       [1moption agent.link-selection [4m[22mip-address[24m[1m;[0m

         The link-selection suboption is provided by relay agents to inform
         servers what subnet the client is actually attached to.  This is
         useful in those cases where the giaddr (where responses must be sent
         to the relay agent) is not on the same subnet as the client.  When
         this option is present in a packet from a relay agent, the DHCP
         server will use its contents to find a subnet declared in
         configuration, and from here take one step further backwards to any
         shared-network the subnet may be defined within...the client may be
         given any address within that shared network, as normally
         appropriate.

[1mTHE CLIENT FQDN SUBOPTIONS[0m
       The Client FQDN option, currently defined in the Internet Draft draft-
       ietf-dhc-fqdn-option-00.txt is not a standard yet, but is in
       sufficiently wide use already that we have implemented it.   Due to the
       complexity of the option format, we have implemented it as a suboption
       space rather than a single option.   In general this option should not
       be configured by the user - instead it should be used as part of an
       automatic DNS update system.

       [1moption fqdn.no-client-update [4m[22mflag[24m[1m;[0m

         When the client sends this, if it is true, it means the client will
         not attempt to update its A record.   When sent by the server to the
         client, it means that the client [4mshould[24m [4mnot[24m update its own A record.

       [1moption fqdn.server-update [4m[22mflag[24m[1m;[0m

         When the client sends this to the server, it is requesting that the
         server update its A record.   When sent by the server, it means that
         the server has updated (or is about to update) the client's A record.

       [1moption fqdn.encoded [4m[22mflag[24m[1m;[0m

         If true, this indicates that the domain name included in the option
         is encoded in DNS wire format, rather than as plain ASCII text.   The
         client normally sets this to false if it doesn't support DNS wire
         format in the FQDN option.   The server should always send back the
         same value that the client sent.   When this value is set on the
         configuration side, it controls the format in which the [4mfqdn.fqdn[0m
         suboption is encoded.

       [1moption fqdn.rcode1 [4m[22mflag[24m[1m;[0m

       [1moption fqdn.rcode2 [4m[22mflag[24m[1m;[0m

         These options specify the result of the updates of the A and PTR
         records, respectively, and are only sent by the DHCP server to the
         DHCP client.  The values of these fields are those defined in the DNS
         protocol specification.

       [1moption fqdn.fqdn [4m[22mtext[24m[1m;[0m

         Specifies the domain name that the client wishes to use.   This can
         be a fully-qualified domain name, or a single label.   If there is no
         trailing generally update that name in some locally-defined domain.

       [1moption fqdn.hostname [4m[22m--never[24m [4mset--[24m[1m;[0m

         This option should never be set, but it can be read back using the
         [1moption [22mand [1mconfig-option [22moperators in an expression, in which case it
         returns the first label in the [1mfqdn.fqdn [22msuboption - for example, if
         the value of [1mfqdn.fqdn [22mis "foo.example.com.", then [1mfqdn.hostname [22mwill
         be "foo".

       [1moption fqdn.domainname [4m[22m--never[24m [4mset--[24m[1m;[0m

         This option should never be set, but it can be read back using the
         [1moption [22mand [1mconfig-option [22moperators in an expression, in which case it
         returns all labels after the first label in the [1mfqdn.fqdn [22msuboption -
         for example, if the value of [1mfqdn.fqdn [22mis "foo.example.com.", then
         [1mfqdn.hostname [22mwill be "example.com.".   If this suboption value is
         not set, it means that an unqualified name was sent in the fqdn
         option, or that no fqdn option was sent at all.

       If you wish to use any of these suboptions, we strongly recommend that
       you refer to the Client FQDN option draft (or standard, when it becomes
       a standard) - the documentation here is sketchy and incomplete in
       comparison, and is just intended for reference by people who already
       understand the Client FQDN option specification.

[1mTHE NETWARE/IP SUBOPTIONS[0m
       RFC2242 defines a set of encapsulated options for Novell NetWare/IP
       clients.  To use these options in the dhcp server, specify the option
       space name, "nwip", followed by a period, followed by the option name.
       The following options can be specified:

       [1moption nwip.nsq-broadcast [4m[22mflag[24m[1m;[0m

         If true, the client should use the NetWare Nearest Server Query to
         locate a NetWare/IP server.   The behaviour of the Novell client if
         this suboption is false, or is not present, is not specified.

       [1moption nwip.preferred-dss [4m[22mip-address[24m [[1m, [4m[22mip-address[24m... ][1m;[0m

         This suboption specifies a list of up to five IP addresses, each of
         which should be the IP address of a NetWare Domain SAP/RIP server
         (DSS).

       [1moption nwip.nearest-nwip-server [4m[22mip-address[0m
                                    [[1m, [4m[22mip-address[24m...][1m;[0m

         This suboption specifies a list of up to five IP addresses, each of
         which should be the IP address of a Nearest NetWare IP server.

       [1moption nwip.autoretries [4m[22muint8[24m[1m;[0m

         Specifies the number of times that a NetWare/IP client should attempt
         to communicate with a given DSS server at startup.

       [1moption nwip.autoretry-secs [4m[22muint8[24m[1m;[0m

         Specifies the number of seconds that a Netware/IP client should wait
         between retries when attempting to establish communications with a
         DSS server at startup.

       [1moption nwip.nwip-1-1 [4m[22muint8[24m[1m;[0m

         If true, the NetWare/IP client should support NetWare/IP version 1.1
         compatibility.   This is only needed if the client will be contacting
         Netware/IP version 1.1 servers.

       [1moption nwip.primary-dss [4m[22mip-address[24m[1m;[0m

         Specifies the IP address of the Primary Domain SAP/RIP Service server
         (DSS) for this NetWare/IP domain.   The NetWare/IP administration
         utility uses this value as Primary DSS server when configuring a
         secondary DSS server.

[1mDEFINING NEW OPTIONS[0m
       The Internet Systems Consortium DHCP client and server provide the
       capability to define new options.   Each DHCP option has a name, a
       code, and a structure.   The name is used by you to refer to the
       option.   The code is a number, used by the DHCP server and client to
       refer to an option.   The structure describes what the contents of an
       option looks like.

       To define a new option, you need to choose a name for it that is not in
       use for some other option - for example, you can't use "host-name"
       because the DHCP protocol already defines a host-name option, which is
       documented earlier in this manual page.   If an option name doesn't
       appear in this manual page, you can use it, but it's probably a good
       idea to put some kind of unique string at the beginning so you can be
       sure that future options don't take your name.   For example, you might
       define an option, "local-host-name", feeling some confidence that no
       official DHCP option name will ever start with "local".

       Once you have chosen a name, you must choose a code.  All codes between
       224 and 254 are reserved as 'site-local' DHCP options, so you can pick
       any one of these for your site (not for your product/application).  In
       RFC3942, site-local space was moved from starting at 128 to starting at
       224.  In practice, some vendors have interpreted the protocol rather
       loosely and have used option code values greater than 128 themselves.
       There's no real way to avoid this problem, and it was thought to be
       unlikely to cause too much trouble in practice.  If you come across a
       vendor-documented option code in either the new or old site-local
       spaces, please contact your vendor and inform them about rfc3942.

       The structure of an option is simply the format in which the option
       data appears.   The ISC DHCP server currently supports a few simple
       types, like integers, booleans, strings and IP addresses, and it also
       supports the ability to define arrays of single types or arrays of
       fixed sequences of types.

       New options are declared as follows:

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= [4m[22mdefinition[24m [1m;[0m

       The values of [4mnew-name[24m and [4mnew-code[24m should be the name you have chosen
       for the new option and the code you have chosen.   The [4mdefinition[0m
       should be the definition of the structure of the option.

       The following simple option type definitions are supported:

       [1mBOOLEAN[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= boolean ;[0m

       An option of type boolean is a flag with a value of either on or off
       (or true or false).   So an example use of the boolean type would be:

       option use-zephyr code 180 = boolean;
       option use-zephyr on;

       [1mINTEGER[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= [4m[22msign[24m [1minteger [4m[22mwidth[24m [1m;[0m

       The [4msign[24m token should either be blank, [4munsigned[24m or [4msigned[24m.   The width
       can be either 8, 16 or 32, and refers to the number of bits in the
       integer.   So for example, the following two lines show a definition of
       the sql-connection-max option and its use:

       option sql-connection-max code 192 = unsigned integer 16;
       option sql-connection-max 1536;

       [1mIP-ADDRESS[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= ip-address ;[0m

       An option whose structure is an IP address can be expressed either as a
       domain name or as a dotted quad.  So the following is an example use of
       the ip-address type:

       option sql-server-address code 193 = ip-address;
       option sql-server-address sql.example.com;


       [1mTEXT[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= text ;[0m

       An option whose type is text will encode an ASCII text string.   For
       example:

       option sql-default-connection-name code 194 = text;
       option sql-default-connection-name "PRODZA";


       [1mDATA STRING[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= string ;[0m

       An option whose type is a data string is essentially just a collection
       of bytes, and can be specified either as quoted text, like the text
       type, or as a list of hexadecimal contents separated by colons whose
       values must be between 0 and FF.   For example:

       option sql-identification-token code 195 = string;
       option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;


       [1mDOMAIN-LIST[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= domain-list ;[0m

       An option whose type is [1mdomain-list [22mis an RFC1035 formatted (on the
       wire, "DNS Format") list of domain names, separated by root labels.

       Note that when [1mdomain-list [22mformatted options are output as environment
       variables to [1mdhclient-script(8), [22mthe standard DNS -escape mechanism is
       used: they are decimal.  This is appropriate for direct use in e.g.
       /etc/resolv.conf.


       [1mENCAPSULATION[0m

       [1moption [4m[22mnew-name[24m [1mcode [4m[22mnew-code[24m [1m= encapsulate [4m[22midentifier[24m [1m;[0m

       An option whose type is [1mencapsulate [22mwill encapsulate the contents of
       the option space specified in [4midentifier[24m.   Examples of encapsulated
       options in the DHCP protocol as it currently exists include the vendor-
       encapsulated-options option, the netware-suboptions option and the
       relay-agent-information option.

       option space local;
       option local.demo code 1 = text;
       option local-encapsulation code 197 = encapsulate local;
       option local.demo "demo";


       [1mARRAYS[0m

       Options can contain arrays of any of the above types except for the
       text and data string types, which aren't currently supported in arrays.
       An example of an array definition is as follows:

       option kerberos-servers code 200 = array of ip-address;
       option kerberos-servers 10.20.10.1, 10.20.11.1;

       [1mRECORDS[0m

       Options can also contain data structures consisting of a sequence of
       data types, which is sometimes called a record type.   For example:

       option contrived-001 code 201 = { boolean, integer 32, text };
       option contrived-001 on 1772 "contrivance";

       It's also possible to have options that are arrays of records, for
       example:

       option new-static-routes code 201 = array of {
            ip-address, ip-address, ip-address, integer 8 };
       option static-routes
            10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
            10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
            10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;


[1mVENDOR ENCAPSULATED OPTIONS[0m
       The DHCP protocol defines the  [1mvendor-encapsulated-options [22moption,
       which allows vendors to define their own options that will be sent
       encapsulated in a standard DHCP option.   The format of the [1mvendor-[0m
       [1mencapsulated-options [22moption is either a series of bytes whose format is
       not specified, or a sequence of options, each of which consists of a
       single-byte vendor-specific option code, followed by a single-byte
       length, followed by as many bytes of data as are specified in the
       length (the length does not include itself or the option code).

       The value of this option can be set in one of two ways.   The first way
       is to simply specify the data directly, using a text string or a colon-
       separated list of hexadecimal values.   For example:

       option vendor-encapsulated-options
           2:4:AC:11:41:1:
           3:12:73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
           4:12:2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;

       The second way of setting the value of this option is to have the DHCP
       server generate a vendor-specific option buffer.   To do this, you must
       do four things: define an option space, define some options in that
       option space, provide values for them, and specify that that option
       space should be used to generate the [1mvendor-encapsulated-options[0m
       option.

       To define a new option space in which vendor options can be stored, use
       the option space statement:

       [1moption space [4m[22mname[24m [1m[ [ code width [4m[22mnumber[24m [1m] [ length width [4m[22mnumber[24m [1m] [[0m
       [1mhash size [4m[22mnumber[24m [1m] ] ;[0m

       Where the numbers following [1mcode width[22m, [1mlength width[22m, and [1mhash size[0m
       respectively identify the number of bytes used to describe option
       codes, option lengths, and the size in buckets of the hash tables to
       hold options in this space.

       The code and length widths are used in DHCP protocol - you must
       configure these numbers to match the applicable option space you are
       configuring.  They each default to 1.  Valid values for code widths are
       1, 2 or 4.  Valid values for length widths are 1 or 2.

       The hash size defaults depend upon the [1mcode width [22mselected, and may be
       254 or 1009.  Valid values range between 1 and 65535.  Note that the
       higher you configure this value, the more memory will be used.  It is
       considered good practice to configure a value that is slightly larger
       than the estimated number of options you plan to configure within the
       space.  Due to limitations in previous versions of ISC DHCP (up to and
       including DHCP 3.0.*), this value was fixed at 9973.

       The name can then be used in option definitions, as described earlier
       in this document.   For example:

       option space SUNW code width 1 length width 1 hash size 3;
       option SUNW.server-address code 2 = ip-address;
       option SUNW.server-name code 3 = text;
       option SUNW.root-path code 4 = text;

       Once you have defined an option space and the format of some options,
       you can set up scopes that define values for those options, and you can
       say when to use them.   For example, suppose you want to handle two
       different classes of clients.   Using the option space definition shown
       in the previous example, you can send different option values to
       different clients based on the vendor-class-identifier option that the
       clients send, as follows:

       class "vendor-classes" {
         match option vendor-class-identifier;
       }

       option SUNW.server-address 172.17.65.1;
       option SUNW.server-name "sundhcp-server17-1";

       subclass "vendor-classes" "SUNW.Ultra-5_10" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/sparc";
       }

       subclass "vendor-classes" "SUNW.i86pc" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/i86pc";
       }

       As you can see in the preceding example, regular scoping rules apply,
       so you can define values that are global in the global scope, and only
       define values that are specific to a particular class in the local
       scope.   The [1mvendor-option-space [22mdeclaration tells the DHCP server to
       use options in the SUNW option space to construct the [1mvendor-[0m
       [1mencapsulated-options [22moption.

[1mSEE ALSO[0m
       dhcpd.conf(5), dhcpd.leases(5), dhclient.conf(5), dhcp-eval(5),
       dhcpd(8), dhclient(8), RFC2132, RFC2131, draft-ietf-dhc-agent-
       options-??.txt.

[1mAUTHOR[0m
       The Internet Systems Consortium DHCP Distribution was written by Ted
       Lemon under a contract with Vixie Labs.  Funding for this project was
       provided through Internet Systems Consortium.  Information about
       Internet Systems Consortium can be found at [1mhttps://www.isc.org.[0m



                                                              dhcpd-options(5)
