


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, 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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