


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


NNAAMMEE
       dhcp-options - Dynamic Host Configuration Protocol options

DDEESSCCRRIIPPTTIIOONN
       The Dynamic Host Configuration protocol allows the  client
       to  receive  ooppttiioonnss  from  the DHCP server describing the
       network configuration and various services that are avail-
       able  on  the  network.    When  configuring  ddhhccppdd((88))  or
       ddhhcclliieenntt((88)) ,, options must often be declared.   The syntax
       for  declaring  options,  and the names and formats of the
       options that can be declared, are documented here.

RREEFFEERREENNCCEE:: OOPPTTIIOONN SSTTAATTEEMMEENNTTSS
       DHCP _o_p_t_i_o_n statements always start with the  _o_p_t_i_o_n  key-
       word, 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 iipp--aaddddrreessss data 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 iinntt3322 data type specifies  a  signed  32-bit  integer.
       The uuiinntt3322 data type specifies an unsigned 32-bit integer.
       The  iinntt1166  and  uuiinntt1166  data  types  specify  signed  and
       unsigned  16-bit integers.   The iinntt88 and uuiinntt88 data types
       specify signed  and  unsigned  8-bit  integers.   Unsigned
       8-bit integers are also sometimes referred to as octets.

       The  tteexxtt  data  type specifies an NVT ASCII string, which
       must be enclosed in double quotes - for example, to  spec-
       ify a root-path option, the syntax would be

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

       The  ddoommaaiinn--nnaammee  data 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 ddoommaaiinn--lliisstt data  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 ffllaagg data type specifies a boolean  value.    Booleans



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


       can  be  either true or false (or on or off, if that makes
       more sense to you).

       The ssttrriinngg data 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;

SSEETTTTIINNGG OOPPTTIIOONN VVAALLUUEESS UUSSIINNGG EEXXPPRREESSSSIIOONNSS
       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 ddhhccpp--
       eevvaall((55))  manual  page  describes how to write expressions.
       To assign the result of an evaluation to an option, define
       the option as follows:

         ooppttiioonn _m_y_-_o_p_t_i_o_n == _e_x_p_r_e_s_s_i_o_n ;;

       For example:

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

SSTTAANNDDAARRDD DDHHCCPP OOPPTTIIOONNSS
       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 imple-
       mented, 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 infor-
       mation.

       Some of the options documented here are automatically gen-
       erated 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 condi-
       tional expressions. However, the value of the option  can-
       not  be  used  in  the  configuration  file of the sending
       agent, because the value is determined only _a_f_t_e_r the con-
       figuration file has been processed. In the following docu-
       mentation, such options will be shown as "not user config-
       urable"

       The standard options are:

       ooppttiioonn aallll--ssuubbnneettss--llooccaall _f_l_a_g;;

          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



                                                                2





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


          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 con-
          nected network may have smaller MTUs.

       ooppttiioonn aarrpp--ccaacchhee--ttiimmeeoouutt _u_i_n_t_3_2;;

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

       ooppttiioonn bbccmmss--ccoonnttrroolllleerr--aaddddrreessss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...
       ];;

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

       ooppttiioonn bboooottffiillee--nnaammee _t_e_x_t;;

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

       ooppttiioonn bboooott--ssiizzee _u_i_n_t_1_6;;

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

       ooppttiioonn bbrrooaaddccaasstt--aaddddrreessss _i_p_-_a_d_d_r_e_s_s;;

          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).

       ooppttiioonn ccooookkiiee--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn ddeeffaauulltt--iipp--ttttll _u_i_n_t_8_;

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

       ooppttiioonn ddeeffaauulltt--ttccpp--ttttll _u_i_n_t_8;;

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




                                                                3





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


       ooppttiioonn ddeeffaauulltt--uurrll _s_t_r_i_n_g;;

          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.

       ooppttiioonn ddhhccpp--cclliieenntt--iiddeennttiiffiieerr _s_t_r_i_n_g;;

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

          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";

       ooppttiioonn ddhhccpp--lleeaassee--ttiimmee _u_i_n_t_3_2;;

          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 (DHCPOF-
          FER), 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 _m_a_x_-_l_e_a_s_e_-_t_i_m_e and  _d_e_f_a_u_l_t_-_l_e_a_s_e_-
          _t_i_m_e server options in ddhhccppdd..ccoonnff((55))..

       ooppttiioonn ddhhccpp--mmaaxx--mmeessssaaggee--ssiizzee _u_i_n_t_1_6;;

          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.

       ooppttiioonn ddhhccpp--mmeessssaaggee _t_e_x_t;;

          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.



                                                                4





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


          This option is not user configurable.

       ooppttiioonn ddhhccpp--mmeessssaaggee--ttyyppee _u_i_n_t_8;;

          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.

       ooppttiioonn ddhhccpp--ooppttiioonn--oovveerrllooaadd _u_i_n_t_8;;

          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 inter-
          pretation 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.


       ooppttiioonn ddhhccpp--ppaarraammeetteerr--rreeqquueesstt--lliisstt _u_i_n_t_1_6;;

          This option, when sent by the client,  specifies  which
          options  the client wishes the server to return.   Nor-
          mally, in the ISC DHCP client, this is done  using  the
          _r_e_q_u_e_s_t 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



                                                                5





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


          normally return.

       ooppttiioonn ddhhccpp--rreebbiinnddiinngg--ttiimmee _u_i_n_t_3_2;;

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

          This option is not user configurable.


       ooppttiioonn ddhhccpp--rreenneewwaall--ttiimmee _u_i_n_t_3_2;;

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

          This option is not user configurable.


       ooppttiioonn ddhhccpp--rreeqquueesstteedd--aaddddrreessss _i_p_-_a_d_d_r_e_s_s;;

          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.


       ooppttiioonn ddhhccpp--sseerrvveerr--iiddeennttiiffiieerr _i_p_-_a_d_d_r_e_s_s;;

          This  option  is used in DHCPOFFER and DHCPREQUEST mes-
          sages, 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  dis-
          tinguish  between  lease  offers.  DHCP clients use the
          contents of the 'server identifier' field as the desti-
          nation  address  for  any  DHCP messages unicast to the
          DHCP server.  DHCP clients also indicate which of  sev-
          eral  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
          _s_e_r_v_e_r_-_i_d_e_n_t_i_f_i_e_r server option in _d_h_c_p_d_._c_o_n_f_(_5_)_.


       ooppttiioonn ddoommaaiinn--nnaammee _t_e_x_t;;

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




                                                                6





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


       ooppttiioonn ddoommaaiinn--nnaammee--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

          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.

       ooppttiioonn ddoommaaiinn--sseeaarrcchh _d_o_m_a_i_n_-_l_i_s_t;;

          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";

       ooppttiioonn eexxtteennssiioonnss--ppaatthh _t_e_x_t;;

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

       ooppttiioonn ffiinnggeerr--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn ffoonntt--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn hhoosstt--nnaammee _s_t_r_i_n_g;;

          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
          ddhhcclliieenntt--ssccrriipptt((88))  if  the  hostname  for  the  client
          machine is not set.

       ooppttiioonn iieeeeee880022--33--eennccaappssuullaattiioonn _f_l_a_g;;

          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



                                                                7





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


          client should use RFC 1042 encapsulation.

       ooppttiioonn iieenn111166--nnaammee--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];

          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.

       ooppttiioonn iimmpprreessss--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn iinntteerrffaaccee--mmttuu _u_i_n_t_1_6;;

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

       ooppttiioonn iipp--ffoorrwwaarrddiinngg _f_l_a_g;;

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

       ooppttiioonn iirrcc--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn lloogg--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

          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.

       ooppttiioonn llpprr--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s  [,, _i_p_-_a_d_d_r_e_s_s...  ];;

          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.

       ooppttiioonn mmaasskk--ssuupppplliieerr _f_l_a_g;;

          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.

       ooppttiioonn mmaaxx--ddggrraamm--rreeaasssseemmbbllyy _u_i_n_t_1_6;;

          This option specifies the maximum  size  datagram  that



                                                                8





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


          the client should be prepared to reassemble.  The mini-
          mum legal value is 576.

       ooppttiioonn mmeerriitt--dduummpp _t_e_x_t;;

          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 charac-
          ter  string consisting of characters from the NVT ASCII
          character set.

       ooppttiioonn mmoobbiillee--iipp--hhoommee--aaggeenntt _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

          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 nor-
          mally there will be only one such agent.

       ooppttiioonn nnddss--ccoonntteexxtt _s_t_r_i_n_g;;

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

       ooppttiioonn nnddss--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn nnddss--ttrreeee--nnaammee _s_t_r_i_n_g;;

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

       ooppttiioonn nneettbbiiooss--dddd--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn nneettbbiiooss--nnaammee--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...];;

          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.

       ooppttiioonn nneettbbiiooss--nnooddee--ttyyppee _u_i_n_t_8;;

          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.




                                                                9





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


          Possible node types are:


          _1    B-node: Broadcast - no WINS

          _2    P-node: Peer - WINS only

          _4    M-node: Mixed - broadcast, then WINS

          _8    H-node: Hybrid - WINS, then broadcast

       ooppttiioonn nneettbbiiooss--ssccooppee _s_t_r_i_n_g;;

          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.

       ooppttiioonn  nneettiinnffoo--sseerrvveerr--aaddddrreessss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...
       ];;

          The  nneettiinnffoo--sseerrvveerr--aaddddrreessss   option   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.

       ooppttiioonn nneettiinnffoo--sseerrvveerr--ttaagg _t_e_x_t;;

          The nneettiinnffoo--sseerrvveerr--ttaagg option 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.

       ooppttiioonn nniiss--ddoommaaiinn _t_e_x_t;;

          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  charac-
          ters from the NVT ASCII character set.

       ooppttiioonn nniiss--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn nniisspplluuss--ddoommaaiinn _t_e_x_t;;

          This  option  specifies  the  name of the client's NIS+
          domain.  The domain is formatted as a character  string



                                                               10





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


          consisting  of  characters from the NVT ASCII character
          set.

       ooppttiioonn nniisspplluuss--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn nnnnttpp--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn nnoonn--llooccaall--ssoouurrccee--rroouuttiinngg _f_l_a_g;;

          This option specifies whether the client should config-
          ure  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 dis-
          allow forwarding of such datagrams, and a value of true
          means allow forwarding.

       ooppttiioonn nnttpp--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

          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.

       ooppttiioonn nnwwiipp--ddoommaaiinn _s_t_r_i_n_g;;

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

       ooppttiioonn nnwwiipp--ssuubbooppttiioonnss _s_t_r_i_n_g;;

          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.

       ooppttiioonn ppaatthh--mmttuu--aaggiinngg--ttiimmeeoouutt _u_i_n_t_3_2;;

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

       ooppttiioonn ppaatthh--mmttuu--ppllaatteeaauu--ttaabbllee _u_i_n_t_1_6 [,, _u_i_n_t_1_6...  ];;

          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



                                                               11





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


          minimum MTU value cannot be smaller than 68.

       ooppttiioonn ppeerrffoorrmm--mmaasskk--ddiissccoovveerryy _f_l_a_g;;

          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.

       ooppttiioonn ppoolliiccyy--ffiilltteerr _i_p_-_a_d_d_r_e_s_s _i_p_-_a_d_d_r_e_s_s
                         [,, _i_p_-_a_d_d_r_e_s_s _i_p_-_a_d_d_r_e_s_s...];;

          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.

       ooppttiioonn ppoopp--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn rreessoouurrccee--llooccaattiioonn--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s
                                     [,, _i_p_-_a_d_d_r_e_s_s...];;

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

       ooppttiioonn rroooott--ppaatthh _t_e_x_t;;

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

       ooppttiioonn rroouutteerr--ddiissccoovveerryy _f_l_a_g;;

          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.

       ooppttiioonn rroouutteerr--ssoolliicciittaattiioonn--aaddddrreessss _i_p_-_a_d_d_r_e_s_s;;



                                                               12





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


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

       ooppttiioonn rroouutteerrss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn   ssllpp--ddiirreeccttoorryy--aaggeenntt  _b_o_o_l_e_a_n  _i_p_-_a_d_d_r_e_s_s  [,,  _i_p_-
       _a_d_d_r_e_s_s... ];;

          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  proto-
          col.

          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.

       ooppttiioonn ssllpp--sseerrvviiccee--ssccooppee _b_o_o_l_e_a_n _t_e_x_t;;

          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 omit-
          ted, in which case the SLP Agent will  use  the  aggre-
          gated  list  of scopes of all directory agents known to
          the SLP agent.

       ooppttiioonn ssmmttpp--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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




                                                               13





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


       ooppttiioonn ssttaattiicc--rroouutteess _i_p_-_a_d_d_r_e_s_s _i_p_-_a_d_d_r_e_s_s
                         [,, _i_p_-_a_d_d_r_e_s_s _i_p_-_a_d_d_r_e_s_s...];;

          This option specifies a list of static routes that  the
          client  should install in its routing cache.  If multi-
          ple 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  sec-
          ond 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  rroouutteerrss  option.    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  stan-
          dard,  this  option  is  virtually  useless, and is not
          implemented by any of the  popular  DHCP  clients,  for
          example the Microsoft DHCP client.

       ooppttiioonn ssttrreeeettttaallkk--ddiirreeccttoorryy--aassssiissttaannccee--sseerrvveerr _i_p_-_a_d_d_r_e_s_s
                                                  [,, _i_p_-_a_d_d_r_e_s_s...];;

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

       ooppttiioonn ssttrreeeettttaallkk--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn ssuubbnneett--mmaasskk _i_p_-_a_d_d_r_e_s_s;;

          The subnet mask option specifies  the  client's  subnet
          mask  as per RFC 950.  If no subnet mask option is pro-
          vided 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.   How-
          ever,  _a_n_y  subnet-mask  option  declaration that is in
          scope for the address being assigned will override  the
          subnet mask specified in the subnet declaration.

       ooppttiioonn ssuubbnneett--sseelleeccttiioonn _s_t_r_i_n_g;;

          Sent  by the client if an address is required in a sub-
          net 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



                                                               14





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


          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.


       ooppttiioonn sswwaapp--sseerrvveerr _i_p_-_a_d_d_r_e_s_s;;

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

       ooppttiioonn ttccpp--kkeeeeppaalliivvee--ggaarrbbaaggee _f_l_a_g;;

          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.

       ooppttiioonn ttccpp--kkeeeeppaalliivvee--iinntteerrvvaall _u_i_n_t_3_2;;

          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.

       ooppttiioonn ttffttpp--sseerrvveerr--nnaammee _t_e_x_t;;

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

       ooppttiioonn ttiimmee--ooffffsseett _i_n_t_3_2;;

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

       ooppttiioonn ttiimmee--sseerrvveerrss _i_p_-_a_d_d_r_e_s_s [, _i_p_-_a_d_d_r_e_s_s...  ];;

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

       ooppttiioonn ttrraaiilleerr--eennccaappssuullaattiioonn _f_l_a_g;;

          This option specifies whether or not the client  should



                                                               15





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


          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 trail-
          ers.

       ooppttiioonn uuaapp--sseerrvveerrss _t_e_x_t;;

          This  option specifies a list of URLs, each pointing to
          a user authentication service that is capable  of  pro-
          cessing  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 compo-
          nent, 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.

       ooppttiioonn uusseerr--ccllaassss _s_t_r_i_n_g;;

          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 spec-
          ified  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.

       ooppttiioonn vveennddoorr--ccllaassss--iiddeennttiiffiieerr _s_t_r_i_n_g;;

          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  fol-
          lowing 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  vveennddoorr--eennccaappssuullaatteedd--ooppttiioonnss  option.
          Please  see  the  VENDOR  ENCAPSULATED  OPTIONS section
          later in this manual page for further information.



                                                               16





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


       ooppttiioonn vveennddoorr--eennccaappssuullaatteedd--ooppttiioonnss _s_t_r_i_n_g;;

          The  vveennddoorr--eennccaappssuullaatteedd--ooppttiioonnss  option  can   contain
          either  a  single  vendor-specific value or one or more
          vendor-specific suboptions.   This option is  not  nor-
          mally 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 ven-
          dors  (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.

       ooppttiioonn wwwwww--sseerrvveerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

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

       ooppttiioonn xx--ddiissppllaayy--mmaannaaggeerr _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s...  ];;

          This option specifies a list of systems that  are  run-
          ning the X Window System Display Manager and are avail-
          able to the client.   Addresses  should  be  listed  in
          order of preference.

RREELLAAYY AAGGEENNTT IINNFFOORRMMAATTIIOONN OOPPTTIIOONN
       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 permissi-
       ble.   These options are not supported in the client.

       ooppttiioonn aaggeenntt..cciirrccuuiitt--iidd _s_t_r_i_n_g;;

          The circuit-id suboption encodes an agent-local identi-
          fier  of the circuit from which a DHCP client-to-server
          packet was received.  It is intended for use by  agents



                                                               17





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


          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 possibil-
          ity of standardizing the format in the future.

       ooppttiioonn aaggeenntt..rreemmoottee--iidd _s_t_r_i_n_g;;

          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.

       ooppttiioonn aaggeenntt..DDOOCCSSIISS--ddeevviiccee--ccllaassss _u_i_n_t_3_2;;

          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.

       ooppttiioonn aaggeenntt..lliinnkk--sseelleeccttiioonn _i_p_-_a_d_d_r_e_s_s;;

          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.

TTHHEE CCLLIIEENNTT FFQQDDNN SSUUBBOOPPTTIIOONNSS
       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 for-
       mat,  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



                                                               18





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


       part of an automatic DNS update system.

       ooppttiioonn ffqqddnn..nnoo--cclliieenntt--uuppddaattee _f_l_a_g;;

          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 _s_h_o_u_l_d _n_o_t update its own A record.

       ooppttiioonn ffqqddnn..sseerrvveerr--uuppddaattee _f_l_a_g;;

          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.

       ooppttiioonn ffqqddnn..eennccooddeedd _f_l_a_g;;

          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 for-
          mat in which the _f_q_d_n_._f_q_d_n suboption is encoded.

       ooppttiioonn ffqqddnn..rrccooddee11 _f_l_a_g;;

       ooppttiioonn ffqqddnn..rrccooddee22 _f_l_a_g;;

          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.

       ooppttiioonn ffqqddnn..ffqqddnn _t_e_x_t;;

          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.

       ooppttiioonn ffqqddnn..hhoossttnnaammee _-_-_n_e_v_e_r _s_e_t_-_-;;

          This  option  should  never  be set, but it can be read
          back using the ooppttiioonn and ccoonnffiigg--ooppttiioonn operators in an
          expression, in which case it returns the first label in
          the ffqqddnn..ffqqddnn suboption - for example, if the value  of
          ffqqddnn..ffqqddnn  is  "foo.example.com.",  then  ffqqddnn..hhoossttnnaammee
          will be "foo".

       ooppttiioonn ffqqddnn..ddoommaaiinnnnaammee _-_-_n_e_v_e_r _s_e_t_-_-;;



                                                               19





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


          This option should never be set, but  it  can  be  read
          back using the ooppttiioonn and ccoonnffiigg--ooppttiioonn operators in an
          expression, in which case it returns all  labels  after
          the  first label in the ffqqddnn..ffqqddnn suboption - for exam-
          ple, if the value of ffqqddnn..ffqqddnn  is  "foo.example.com.",
          then  ffqqddnn..hhoossttnnaammee  will  be "example.com.".   If this
          suboption value is not set, it means that  an  unquali-
          fied  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 documenta-
       tion  here is sketchy and incomplete in comparison, and is
       just intended for reference by people who  already  under-
       stand the Client FQDN option specification.

TTHHEE NNEETTWWAARREE//IIPP SSUUBBOOPPTTIIOONNSS
       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:

       ooppttiioonn nnwwiipp..nnssqq--bbrrooaaddccaasstt _f_l_a_g;;

          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.

       ooppttiioonn nnwwiipp..pprreeffeerrrreedd--ddssss _i_p_-_a_d_d_r_e_s_s [,, _i_p_-_a_d_d_r_e_s_s... ];;

          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).

       ooppttiioonn nnwwiipp..nneeaarreesstt--nnwwiipp--sseerrvveerr _i_p_-_a_d_d_r_e_s_s
                                    [,, _i_p_-_a_d_d_r_e_s_s...];;

          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.

       ooppttiioonn nnwwiipp..aauuttoorreettrriieess _u_i_n_t_8;;

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

       ooppttiioonn nnwwiipp..aauuttoorreettrryy--sseeccss _u_i_n_t_8;;

          Specifies the  number  of  seconds  that  a  Netware/IP
          client  should  wait between retries when attempting to



                                                               20





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


          establish communications with a DSS server at  startup.

       ooppttiioonn nnwwiipp..nnwwiipp--11--11 _u_i_n_t_8;;

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

       ooppttiioonn nnwwiipp..pprriimmaarryy--ddssss _i_p_-_a_d_d_r_e_s_s;;

          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.

DDEEFFIINNIINNGG NNEEWW OOPPTTIIOONNSS
       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 num-
       ber, 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 prob-
       ably 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 offi-
       cial 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  start-
       ing  at  224.   In practice, some vendors have interpreted
       the protocol rather loosely and have used option code val-
       ues  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



                                                               21





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


       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:

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == _d_e_f_i_n_i_t_i_o_n ;;

       The values of _n_e_w_-_n_a_m_e and _n_e_w_-_c_o_d_e should be the name you
       have chosen for the new option and the code you have  cho-
       sen.    The  _d_e_f_i_n_i_t_i_o_n  should  be  the definition of the
       structure of the option.

       The following simple  option  type  definitions  are  sup-
       ported:

       BBOOOOLLEEAANN

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == bboooolleeaann ;;

       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;

       IINNTTEEGGEERR

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == _s_i_g_n iinntteeggeerr _w_i_d_t_h ;;

       The _s_i_g_n token should either be blank, _u_n_s_i_g_n_e_d or _s_i_g_n_e_d.
       The width can be either 8, 16 or 32,  and  refers  to  the
       number  of bits in the integer.   So for example, the fol-
       lowing 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;

       IIPP--AADDDDRREESSSS

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == iipp--aaddddrreessss ;;

       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;


       TTEEXXTT



                                                               22





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


       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == tteexxtt ;;

       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";


       DDAATTAA SSTTRRIINNGG

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == ssttrriinngg ;;

       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 hexadeci-
       mal  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;


       DDOOMMAAIINN--LLIISSTT

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == ddoommaaiinn--lliisstt ;;

       An option whose type is ddoommaaiinn--lliisstt is an RFC1035  format-
       ted (on the wire, "DNS Format") list of domain names, sep-
       arated by root labels.

       Note that when ddoommaaiinn--lliisstt formatted options are output as
       environment  variables to ddhhcclliieenntt--ssccrriipptt((88)),, the standard
       DNS -escape mechanism is used: they are decimal.  This  is
       appropriate for direct use in e.g. /etc/resolv.conf.


       EENNCCAAPPSSUULLAATTIIOONN

       ooppttiioonn _n_e_w_-_n_a_m_e ccooddee _n_e_w_-_c_o_d_e == eennccaappssuullaattee _i_d_e_n_t_i_f_i_e_r ;;

       An  option  whose type is eennccaappssuullaattee will encapsulate the
       contents of the  option  space  specified  in  _i_d_e_n_t_i_f_i_e_r.
       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";





                                                               23





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


       AARRRRAAYYSS

       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;

       RREECCOORRDDSS

       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;


VVEENNDDOORR EENNCCAAPPSSUULLAATTEEDD OOPPTTIIOONNSS
       The DHCP protocol defines the  vveennddoorr--eennccaappssuullaatteedd--ooppttiioonnss
       option,  which  allows vendors to define their own options
       that will be sent encapsulated in a standard DHCP  option.
       The  format  of  the vveennddoorr--eennccaappssuullaatteedd--ooppttiioonnss option 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 hexadeci-
       mal 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



                                                               24





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


       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 vveennddoorr--eennccaappssuullaatteedd--
       ooppttiioonnss option.

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

       ooppttiioonn  ssppaaccee  _n_a_m_e [[ [[ ccooddee wwiiddtthh _n_u_m_b_e_r ]] [[ lleennggtthh wwiiddtthh
       _n_u_m_b_e_r ]] [[ hhaasshh ssiizzee _n_u_m_b_e_r ]] ]] ;;

       Where the numbers following ccooddee wwiiddtthh, lleennggtthh wwiiddtthh,  and
       hhaasshh  ssiizzee  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  ccooddee   wwiiddtthh
       selected,  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 consid-
       ered 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  previ-
       ous 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;
       }




                                                               25





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


       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 vveennddoorr--
       ooppttiioonn--ssppaaccee declaration tells  the  DHCP  server  to  use
       options  in the SUNW option space to construct the vveennddoorr--
       eennccaappssuullaatteedd--ooppttiioonnss option.

SSEEEE AALLSSOO
       dhcpd.conf(5),  dhcpd.leases(5),  dhclient.conf(5),  dhcp-
       eval(5),  dhcpd(8),  dhclient(8), RFC2132, RFC2131, draft-
       ietf-dhc-agent-options-??.txt.

AAUUTTHHOORR
       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 hhttttppss::////wwwwww..iisscc..oorrgg..

























                                                               26


