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dhcpd-options(5)

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NAME    [Toc]    [Back]

       dhcp-options - Dynamic Host Configuration Protocol options

DESCRIPTION    [Toc]    [Back]

       The  Dynamic  Host  Configuration protocol allows the client to receive
       options from the DHCP server describing the network  configuration  and
       various	services that are available 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  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 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  specify	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 example:

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

       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 seperated 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 correctness 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 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.  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.

       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 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  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 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 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 character string consisting of
	 characters from the NVT ASCII character 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 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  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 discovery.  A	value  of  1  means  that  the
	 client should perform mask discovery.

       option mask-supplier flag;

	 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 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 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
	 1305)	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 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 running the X Window
	 System Display Manager and are available 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;

	 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 normally 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 available 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  available  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 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 preference.

SEE ALSO    [Toc]    [Back]

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

AUTHOR    [Toc]    [Back]

       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.  Information about the Internet Software Consortium
 can be found at http://www.isc.org/isc.



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