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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 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.,  haa-
       gen.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  text  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  domain-name	 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 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  string  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:

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

SETTING OPTION VALUES USING EXPRESSIONS
       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 dhcp-eval(5) manual page describes how to
       write expressions.   To assign  the  result  of	an  evaluation	to  an
       option, define the option as follows:

	 option my-option = expression ;

       For example:

	 option hostname = binary-to-ascii (16, 8, "-",
					    substring (hardware, 1, 6));

STANDARD DHCP OPTIONS
       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 after the configuration file has been processed. In the
       following  documentation,  such options will be shown as "not user con-
       figurable"

       The standard options are:

       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  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.

       option arp-cache-timeout uint32;

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

       option bootfile-name text;

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

       option boot-size uint16;

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

       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  sec-
	  tion 3.2.1.3 of STD 3 (RFC1122).

       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 pref-
	  erence.

       option default-ip-ttl uint8;

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

       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 dhcp-client-identifier string;

	  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:

	       option dhcp-client-identifier "\0foo";

	  rather than:

	       option dhcp-client-identifier "foo";

       option dhcp-lease-time uint32;

	  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  max-lease-time  and	default-lease-time  server  options in
	  dhcpd.conf(5).

       option dhcp-max-message-size uint16;

	  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.

       option dhcp-message text;

	  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.

       option dhcp-message-type uint8;

	  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.

       option dhcp-option-overload uint8;

	  This	option	is  used  to  indicate that the DHCP 'sname' or 'file'
	  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.


       option dhcp-parameter-request-list uint16;

	  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 request 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.

       option dhcp-rebinding-time uint32;

	  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.


       option dhcp-renewal-time uint32;

	  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.


       option dhcp-requested-address ip-address;

	  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.


       option dhcp-server-identifier ip-address;

	  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  server-iden-
	  tifier server option in dhcpd.conf(5).


       option domain-name text;

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

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

	  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.

       option extensions-path text;

	  This option specifies the  name  of  a  file	containing  additional
	  options  to  be  interpreted	according to the DHCP option format as
	  specified in RFC2132.

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

	  The Finger server option specifies a list of Finger  servers	avail-
	  able	to  the	 client.  Servers should be listed in order of prefer-
	  ence.

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

	  This option specifies a list of X Window System Font servers	avail-
	  able 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.   This  option is only honored by
	  dhclient-script(8) if the hostname for the  client  machine  is  not
	  set.

       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 false indicates that the
	  client should use RFC 894 encapsulation.  A value of true means that
	  the client should use RFC 1042 encapsulation.

       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 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 pref-
	  erence.

       option interface-mtu uint16;

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

       option ip-forwarding flag;

	  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.

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

	  The IRC server option specifies a list of IRC 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 pref-
	  erence.

       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 mask-supplier flag;

	  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.

       option max-dgram-reassembly uint16;

	  This option specifies the maximum  size  datagram  that  the	client
	  should be prepared to reassemble.  The minimum legal value is 576.

       option merit-dump text;

	  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 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 nds-context string;

	  The  nds-context  option  specifies  the name of the initial Netware
	  Directory Service for an NDS client.

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

	  The nds-servers option specifies a  list  of	IP  addresses  of  NDS
	  servers.

       option nds-tree-name string;

	  The nds-tree-name option specifies NDS tree name that the NDS client
	  should use.

       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-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-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  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

       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 nis-domain text;

	  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.

       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 pref-
	  erence.

       option nisplus-domain text;

	  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 pref-
	  erence.

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

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

       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 false means disallow forwarding of such datagrams, and a value of
	  true means allow forwarding.

       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 nwip-domain string;

	  The  name  of	 the NetWare/IP domain that a NetWare/IP client should
	  use.

       option nwip-suboptions string;

	  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.

       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 perform-mask-discovery flag;

	  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.

       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 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.

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

	  The POP3 server option specifies a list of POP3 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 pref-
	  erence.

       option root-path text;

	  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 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  false indicates that the client should not perform router
	  discovery.  A value of true means that  the  client  should  perform
	  router discovery.

       option router-solicitation-address ip-address;

	  This	option specifies the address to which the client should trans-
	  mit router solicitation requests.

       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 prefer-
	  ence.

       option slp-directory-agent boolean ip-address [, ip-address... ];

	  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.

       option slp-service-scope boolean text;

	  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.

       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 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 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
	  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.
	  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.

	  NOTE to Red Hat dhclient users:
	  The RedHat dhclient-script interprets trailing 0 octets of the  tar-
	  get  as  indicating  the  subnet  class  of  the route - so for this
	  static-routes value:
		  option static-routes 172.0.0.0 172.16.2.254,
				       192.168.0.0 192.168.2.254;
	  the Red Hat dhclient-script will create routes:
		  172/8 via 172.16.2.254 dev $interface
		  192.168/16 via 192.168.2.254 dev $interface
	  which slightly increases the usefulness of the static-routes option.

       option streettalk-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.

       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 pref-
	  erence.

       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 declara-
	  tion 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 subnet-selection string;

	  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.


       option swap-server ip-address;

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

       option tcp-keepalive-garbage flag;

	  This	option	specifies  whether  or	not the client should send TCP
	  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.

       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 tftp-server-name text;

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

       option time-offset int32;

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

       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 pref-
	  erence.

       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  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.

       option uap-servers text;

	  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.

       option user-class string;

	  This	option	is  used  by  some  DHCP clients as a way for users to
	  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.

       option vendor-class-identifier string;

	  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  vendor-
	  encapsulated-options	option.	   Please  see the VENDOR ENCAPSULATED
	  OPTIONS section later in this manual page for further information.

       option vendor-encapsulated-options string;

	  The vendor-encapsulated-options 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.

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

	  The  WWW  server option specifies a list of WWW 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  Win-
	  dow  System  Display	Manager	 and  are  available  to  the  client.
	  Addresses should be listed in order of preference.

RELAY AGENT INFORMATION OPTION
       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.

       option agent.circuit-id string;

	  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.

       option agent.remote-id string;

	  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.

       option agent.DOCSIS-device-class uint32;

	  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.

THE CLIENT FQDN SUBOPTIONS
       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.

       option fqdn.no-client-update flag;

	  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 should not update its own A record.

       option fqdn.server-update flag;

	  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.

       option fqdn.encoded flag;

	  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 fqdn.fqdn
	  suboption is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

	  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.

       option fqdn.fqdn text;

	  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.

       option fqdn.hostname --never set--;

	  This option should never be set, but it can be read back  using  the
	  option  and  config-option operators in an expression, in which case
	  it returns the first label in the fqdn.fqdn suboption - for example,
	  if  the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname
	  will be "foo".

       option fqdn.domainname --never set--;

	  This option should never be set, but it can be read back  using  the
	  option  and  config-option operators in an expression, in which case
	  it returns all labels after the first label in the fqdn.fqdn	subop-
	  tion - for example, if the value of fqdn.fqdn is "foo.example.com.",
	  then fqdn.hostname 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.

THE NETWARE/IP SUBOPTIONS
       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:

       option nwip.nsq-broadcast flag;

	  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.

       option nwip.preferred-dss ip-address [, ip-address... ];

	  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).

       option nwip.nearest-nwip-server ip-address
				    [, ip-address...];

	  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.

       option nwip.autoretries uint8;

	  Specifies the number	of  times  that	 a  NetWare/IP	client	should
	  attempt to communicate with a given DSS server at startup.

       option nwip.autoretry-secs uint8;

	  Specifies the number of seconds that a Netware/IP client should wait
	  between retries when attempting to establish communications  with  a
	  DSS server at startup.

       option nwip.nwip-1-1 uint8;

	  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.

       option nwip.primary-dss ip-address;

	  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.

DEFINING NEW OPTIONS
       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.	For site-local
       options, all codes between 128 and 254 are reserved for	DHCP  options,
       so  you	can  pick  any	one  of these.	In practice, some vendors have
       interpreted the protocol rather loosely and have used option code  val-
       ues  greater  than  128 themselves.   There's no real way to avoid this
       problem, but it's not likely to cause too much trouble in practice.

       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:

       option new-name code new-code = definition ;

       The values of new-name and new-code should be the name you have	chosen
       for  the	 new  option  and  the	code you have chosen.	The definition
       should be the definition of the structure of the option.

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

       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;

       INTEGER

       option new-name code new-code = sign integer width ;

       The  sign token should either be blank, unsigned or signed.   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;

       IP-ADDRESS

       option new-name code new-code = ip-address ;

       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;


       TEXT

       option new-name code new-code = text ;

       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";


       DATA STRING

       option new-name code new-code = string ;

       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;


       ENCAPSULATION

       option new-name code new-code = encapsulate identifier ;

       An option whose type is encapsulate will encapsulate  the  contents  of
       the  option  space  specified in identifier.   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";


       ARRAYS

       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;

       RECORDS

       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";

       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;


VENDOR ENCAPSULATED OPTIONS
       The DHCP	 protocol  defines  the	  vendor-encapsulated-options  option,
       which  allows  vendors  to  define  their own options that will be sent
       encapsulated in a standard DHCP option.	 The  format  of  the  vendor-
       encapsulated-options 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  vendor-encapsulated-options
       option.

       To define a new option space in which vendor options can be stored, use
       the option space statement:

       option space name ;

       The  name  can then be used in option definitions, as described earlier
       in this document.   For example:

       option space SUNW;
       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  vendor-option-space declaration tells the DHCP server to
       use options in the SUNW option space to construct  the  vendor-encapsu-
       lated-options option.

SEE ALSO
       dhcpd.conf(5),	 dhcpd.leases(5),    dhclient.conf(5),	 dhcp-eval(5),
       dhcpd(8),   dhclient(8),	  RFC2132,   RFC2131,	 draft-ietf-dhc-agent-
       options-??.txt.

AUTHOR
       The  Internet  Systems  Consortium DHCP Distribution was written by Ted
       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 http://www.isc.org.



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