


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


NAME
       dhcp-options - DHCP 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, separated by colons.   For exam-
       ple:

            option client-identifier "CLIENT-FOO";
       or
            option 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 sepa-
       rated 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 provided any-
       where in scope, as a last resort dhcpd will use the subnet
       mask  from the subnet declaration for the network on which
       an address is being assigned.   However,  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.




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


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

       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 prefer-
       ence.

        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 Location
       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  restric-
       tions.

        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;




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


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

        option ip-forwarding flag;

       This  option specifies whether the client should configure
       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  configure
       its  IP  layer  to allow forwarding of datagrams with non-
       local source routes (see Section 3.3.5 of [4] for  a  dis-
       cussion  of this topic).  A value of 0 means disallow for-
       warding 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;




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


       This  option  specifies the maximum size datagram that the
       client should be  prepared  to  reassemble.   The  minimum
       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 minimum 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 discov-
       ery.  A value of 1 means that the  client  should  perform
       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 discovery.

        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 multiple
       routes to the same destination  are  specified,  they  are
       listed in descending order of priority.

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

       The  default route (0.0.0.0) is an illegal destination for
       a static route.  To specify the  default  route,  use  the
       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 encapsula-
       tion.  A value of 1 means that the client should  use  RFC



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


       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 connec-
       tions 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 for-
       matted as a character string consisting of characters 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 prefer-
       ence.

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

       The NetBIOS datagram  distribution  server  (NBDD)  option



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


       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.  A value of
       1 corresponds to a NetBIOS B-node; a  value  of  2  corre-
       sponds to a P-node; a value of 4 corresponds to an M-node;
       a value of 8 corresponds to an H-node.

        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  charac-
       ter-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 running
       the X Window System Display Manager and are  available  to
       the  client.  Addresses should be listed in order of pref-
       erence.

        option dhcp-client-identifier data-string;

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

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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