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dhcp-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

	 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...  ];


       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 DHCPREQUEST)
	 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

       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 lim-
	 ited 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.

	 indicate which of several lease offers is being accepted by including
	 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-identi-
	 fier 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 System
	 (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 available
	 to the client.  Servers should be listed in order of preference.

       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	(i.e.,
	 set to the empty string in rc.conf(5) ).

       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.

	 This option specifies the MTU to use on this interface.   The minimum
	 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.

	 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  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 nis-domain text;

	 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  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...  ];


       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 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 subnet
	 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 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.

	 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 transmit
	 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	multi-
	 cast 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	Proto-
	 col  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	preference  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
       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	virtu-
	 ally  useless,  and  is  not  implemented  by any of the popular DHCP
	 clients, for example the Microsoft DHCP client.

       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.  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 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;

	 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 0 indicates that the client should not attempt to use trailers.  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 authen-
	 tication  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 normal
	 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 com-
	 ponent, the path /uap is assumed.   If more than one URL is specified
	 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 spec-
	 ify 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  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-class "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 of the dhcpd.conf manual page for further informa-
	    tion.

	 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 configu-
	    ration file - instead, a vendor class is defined for each  vendor,
	    vendor  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
	    automatically,  but  otherwise  this must be configured manually -
	    see the VENDOR ENCAPSULATED OPTIONS section of the dhcpd.conf man-
	    ual 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
	    Window  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

	 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-spec-
	 ified, and it should generally be assumed to be an opaque object that
	 is  administratively  guaranteed  to be unique to a particular remote
	 end of a circuit.

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 con-
	 figuration side, it controls the format in which the fqdn.fqdn subop-
	 tion is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode1 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 all labels after 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  "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 contacting
	 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 administration
       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;

       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 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;

	 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

       dhclient.conf(5), dhcp-eval(5), dhclient(8), RFC2132, RFC2131.

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.

							      dhcpd-options(5)

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