


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


NAME
       dhcp-options - Dynamic Host Configuration Protocol options

DESCRIPTION
       The Dynamic Host Configuration protocol allows the  client
       to  receive  options  from  the DHCP server describing the
       network configuration and various services that are avail-
       able  on  the  network.    When  configuring  dhcpd(8)  or
       dhclient(8) , 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.

REFERENCE: OPTION STATEMENTS
       DHCP option statements always start with the  option  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 ip-address 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 int32 data type specifies  a  signed  32-bit  integer.
       The uint32 data type specifies an unsigned 32-bit integer.
       The  int16  and  uint16  data  types  specify  signed  and
       unsigned  16-bit integers.   The int8 and uint8 data types
       specify signed  and  unsigned  8-bit  integers.   Unsigned
       8-bit integers are also sometimes referred to as octets.

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

            option domain-name "isc.org";

       The  flag  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  data-string  data  type specifies either an NVT ASCII
       string enclosed in double quotes, or a  series  of  octets
       specified in hexadecimal, seperated by colons.   For exam-
       ple:

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



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


       The documentation for the various options mentioned  below
       is  taken  from  the  latest  IETF  draft document on DHCP
       options.   Options which are not listed  by  name  may  be
       defined  by  the name option-nnn, where nnn is the decimal
       number of the option code.   These options may be followed
       either  by a string, enclosed in quotes, or by a series of
       octets, expressed as two-digit hexadecimal numbers  seper-
       ated by colons.   For example:

            option option-133 "my-option-133-text";
            option option-129 1:54:c9:2b:47;

       Because  dhcpd does not know the format of these undefined
       option codes, no checking is done to ensure  the  correct-
       ness of the entered data.

       The standard options are:

       option subnet-mask ip-address;

          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, any subnet-mask option  declaration  that  is  in
          scope  for the address being assigned will override the
          subnet mask specified in the subnet declaration.

       option time-offset int32;

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

       option routers ip-address [, ip-address...  ];

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

       option time-servers ip-address [, ip-address...  ];

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

       option ien116-name-servers ip-address [, ip-address...  ];

          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.

       option domain-name-servers ip-address [, ip-address...  ];



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


          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.

       option log-servers ip-address [, ip-address...  ];

          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.

       option cookie-servers ip-address [, ip-address...  ];

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

       option lpr-servers ip-address  [, ip-address...  ];

          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.

       option impress-servers ip-address [, ip-address...  ];

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

       option   resource-location-servers   ip-address   [,   ip-
       address...  ];

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

       option host-name string;

          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.

       option boot-size uint16;

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

       option merit-dump string;

          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



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


          character string consisting of characters from the  NVT
          ASCII character set.

       option domain-name string;

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

       option swap-server ip-address;

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

       option root-path string;

          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.

       option ip-forwarding flag;

          This option specifies whether the client should config-
          ure its IP layer for packet forwarding.  A value  of  0
          means  disable  IP  forwarding,  and a value of 1 means
          enable IP forwarding.

       option non-local-source-routing flag;

          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 0 means disallow
          forwarding of such datagrams, and a value  of  1  means
          allow forwarding.

       option  policy-filter  ip-address ip-address [, ip-address
       ip-address...  ];

          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.

       option max-dgram-reassembly uint16;

          This  option  specifies  the maximum size datagram that



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


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

       option default-ip-ttl uint8;

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

       option path-mtu-aging-timeout uint32;

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

       option path-mtu-plateau-table uint16 [, uint16...  ];

          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 mini-
          mum MTU value cannot be smaller than 68.

       option interface-mtu uint16;

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

       option all-subnets-local flag;

          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 1 indicates that all subnets share the same
          MTU.  A value of 0 means that the client should  assume
          that some subnets of the directly connected network may
          have smaller MTUs.

       option broadcast-address ip-address;

          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).

       option perform-mask-discovery flag;

          This  option specifies whether or not the client should
          perform subnet mask discovery using ICMP.  A value of 0
          indicates  that the client should not perform mask dis-
          covery.  A value of 1 means that the client should per-
          form mask discovery.

       option mask-supplier flag;



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


          This  option specifies whether or not the client should
          respond to subnet mask requests using ICMP.  A value of
          0  indicates  that  the  client  should not respond.  A
          value of 1 means that the client should respond.

       option router-discovery flag;

          This option specifies whether or not the client  should
          solicit  routers  using  the Router Discovery mechanism
          defined in RFC 1256.  A value of 0 indicates  that  the
          client should not perform router discovery.  A value of
          1 means that the client should perform  router  discov-
          ery.

       option router-solicitation-address ip-address;

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

       option static-routes ip-address ip-address  [,  ip-address
       ip-address...  ];

          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 routers option.

       option trailer-encapsulation flag;

          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  0  indicates  that  the
          client  should not attempt to use trailers.  A value of
          1 means that the client should attempt to use trailers.

       option arp-cache-timeout uint32;

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

       option ieee802-3-encapsulation flag;

          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 0 indicates that the client should use RFC 894



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


          encapsulation.  A value of  1  means  that  the  client
          should use RFC 1042 encapsulation.

       option default-tcp-ttl uint8;

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

       option tcp-keepalive-interval uint32;

          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.

       option tcp-keepalive-garbage flag;

          This  option  specifies  the  whether or not the client
          should send TCP keepalive  messages  with  a  octet  of
          garbage  for  compatibility with older implementations.
          A value of 0 indicates that a garbage octet should  not
          be  sent.  A  value of 1 indicates that a garbage octet
          should be sent.

       option nis-domain string;

          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.

       option nis-servers ip-address [, ip-address...  ];

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

       option ntp-servers ip-address [, ip-address...  ];

          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.

       option  netbios-name-servers  ip-address  [, ip-address...
       ];

          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



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


          specified using the netbios-name-servers option.

       option netbios-dd-server ip-address [, ip-address...  ];

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

       option netbios-node-type uint8;

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

          Possible node types are:


          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

       option netbios-scope string;

          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.

       option font-servers ip-address [, ip-address...  ];

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

       option x-display-manager ip-address [, ip-address...  ];

          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.

       option dhcp-client-identifier data-string;

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




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


          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.
       option nisplus-servers ip-address [, ip-address...  ];

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

       option tftp-server-name string;

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

       option bootfile-name string;

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

       option mobile-ip-home-agent ip-address [, ip-address... ];

          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.

       option smtp-server ip-address [, ip-address... ];

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

       option pop-server ip-address [, ip-address... ];

          The  POP3 server option specifies a list of POP3 avail-
          able to the client.  Servers should be listed in  order
          of preference.

       option nntp-server ip-address [, ip-address... ];

          The  NNTP server option specifies a list of NNTP avail-
          able to the client.  Servers should be listed in  order
          of preference.

       option www-server ip-address [, ip-address... ];

          The WWW server option specifies a list of WWW available



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


          to the client.  Servers should be listed  in  order  of
          preference.

       option finger-server ip-address [, ip-address... ];

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

       option irc-server ip-address [, ip-address... ];

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

       option streettalk-server ip-address [, ip-address... ];

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

       option streetalk-directory-assistance-server ip-address [,
       ip-address... ];

          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.

SEE ALSO
       dhcpd.conf(5),      dhcpd.leases(5),     dhclient.conf(5),
       dhcpd(8), dhclient(8), RFC2132, RFC2131.

AUTHOR
       dhcpd(8) was written by Ted Lemon <mellon@vix.com> under a
       contract  with  Vixie Labs.   Funding for this project was
       provided by the Internet Software  Corporation.   Informa-
       tion  about  the Internet Software Consortium can be found
       at http://www.isc.org/isc.


















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