


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 available 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  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 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.,  haa-
       gen.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 specify 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  exist-
       ing 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 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, sepa-
       rated by colons.   For example:




                                                                1





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


         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 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  informa-
       tion.

       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 condi-
       tional  expressions. However, the value of the option cannot be used in
       the configuration file of the  sending  agent,  because  the  value  is
       determined only _a_f_t_e_r the configuration file has been processed. In the
       following documentation, such options will be shown as "not  user  con-
       figurable"

       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  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.

       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... ];;




                                                                2





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


          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  declara-
          tion.  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  sec-
          tion 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 pref-
          erence.

       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.

       ooppttiioonn ddeeffaauulltt--uurrll _s_t_r_i_n_g;;

          The  format and meaning of this option is not described in any stan-
          dards 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  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:




                                                                3





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


               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  DHCPRE-
          QUEST)  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  _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.

          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'



                                                                4





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


          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 addi-
          tional 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.


       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.    Normally,  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 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 transitions 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 transitions 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.





                                                                5





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


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

          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  includ-
          ing 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.

       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 Sys-
          tem (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 avail-
          able to the client.  Servers should be listed in  order  of  prefer-
          ence.

       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



                                                                6





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


          available to the client. Servers should be listed in order of  pref-
          erence.

       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 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 pref-
          erence.

       ooppttiioonn iinntteerrffaaccee--mmttuu _u_i_n_t_1_6;;

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

       ooppttiioonn iipp--ffoorrwwaarrddiinngg _f_l_a_g;;

          This  option  specifies  whether  the client should configure its IP
          layer for packet forwarding.  A value of false means disable IP for-
          warding, 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 pref-
          erence.




                                                                7





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


       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 the client
          should be prepared to reassemble.  The minimum 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 character  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 normally 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  initial  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...];;




                                                                8





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


          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 identi-
          fies the client type.

          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 Com-
          puters.  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 charac-
          ter string consisting of characters 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...  ];;




                                                                9





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


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

       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 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 pref-
          erence.

       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  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.

       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  Net-
          Ware/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...  ];;




                                                               10





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


          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.

       ooppttiioonn ppeerrffoorrmm--mmaasskk--ddiissccoovveerryy _f_l_a_g;;

          This option specifies whether or not the client should perform  sub-
          net  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  spec-
          ify  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  Location  servers
          available to the client.  Servers should be listed in order of pref-
          erence.

       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 character 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;;

          This option  specifies  the  address  to  which  the  client  should



                                                               11





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


          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  prefer-
          ence.

       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 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 config-
          ure, 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 pref-
          erence 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.

       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.

       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 multiple routes to the same desti-
          nation are specified, they are listed in descending order of  prior-
          ity.

          The routes consist of a list of IP address pairs.  The first address



                                                               12





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


          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  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 standard, 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 preference.

       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 pref-
          erence.

       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 provided anywhere in scope,  as  a
          last  resort dhcpd will use the subnet mask from the subnet declara-
          tion 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 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.


       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



                                                               13





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


          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  declara-
          tion.    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 pref-
          erence.

       ooppttiioonn ttrraaiilleerr--eennccaappssuullaattiioonn _f_l_a_g;;

          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 trail-
          ers.  A value of true means that the client should  attempt  to  use
          trailers.

       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 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 nor-
          mal 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 spec-
          ified 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



                                                               14





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


          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.

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

       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 normally specified in the DHCP server  configura-
          tion file - instead, a vendor class is defined for each vendor, ven-
          dor 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 (cur-
          rently, the Microsoft Windows 2000 DHCP client) are configured auto-
          matically,  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 running the X  Win-
          dow  System  Display  Manager  and  are  available  to  the  client.
          Addresses should be listed in order of preference.




                                                               15





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


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  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.

       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 partic-
          ular 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



                                                               16





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


          server will use its contents to find a subnet declared in configura-
          tion, 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 suffi-
       ciently wide use already that we have implemented it.   Due to the com-
       plexity  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.

       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 format 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_-_-;;



                                                               17





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 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_-_-;;

          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  subop-
          tion - for example, 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 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  com-
       parison,  and  is  just  intended  for  reference by people who already
       understand 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



                                                               18





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


          between retries when attempting to 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 NetWare/IP version 1.1
          compatibility.   This is only needed if the client will be  contact-
          ing Netware/IP version 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  adminis-
          tration utility uses this value as Primary DSS server when configur-
          ing 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 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:

       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 ;;



                                                               19





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


       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 chosen.   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 supported:

       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 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;

       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

       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 ;;



                                                               20





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


       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;


       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  formatted  (on  the
       wire, "DNS Format") list of domain names, separated 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";


       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";



                                                               21





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


       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 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  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 config-
       ure these numbers to match the applicable option space you are  config-
       uring.   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



                                                               22





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


       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 dif-
       ferent 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 vveennddoorr--ooppttiioonn--ssppaaccee declaration tells the DHCP  server  to
       use  options  in the SUNW option space to construct the vveennddoorr--eennccaappssuu--
       llaatteedd--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



                                                               23





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


       Lemon  under  a contract with Vixie Labs.  Funding for this project was
       provided through Internet Systems Consortium.  Information about Inter-
       net Systems Consortium can be found at hhttttppss::////wwwwww..iisscc..oorrgg..






















































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