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dhcp-options(5)						       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 spec‐
       ify  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   ip6-address   data	  specifies  an	 IPv6  address,	 like  ::1  or
       3ffe:bbbb:aaaa:aaaa::1.

       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  be
       enclosed	 in  double  quotes.   The domain name is stored just as if it
       were a text option.

       The domain-list data type specifies a list of domain names, enclosed in
       double  quotes  and  separated  by  commas  ("example.com",  "foo.exam‐
       ple.com").

       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));

INCLUDING OPTION DEFINITIONS
       Starting	 with 4.3.0 when ISC adds new option definitions those defini‐
       tions will be included in the code based on the definition of an	 argu‐
       ment for the RFC that defines the option in includes/site.h.  This pro‐
       vides you with a method for over-riding the ISC definitions  if	neces‐
       sary  -	for  example  if you have previously defined the option with a
       different format using the mechanism from DEFINING NEW OPTIONS below.

       By default all of the options are enabled.   In	order  to  disable  an
       option you would edit the includes/site.h file and comment out the def‐
       inition for the proper RFC.

STANDARD DHCPV4 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 associated-ip ip-address [, ip-address... ];

	 This  option is part of lease query.  It is used to return all of the
	 IP addresses associated with a given DHCP client.

	 This option is not user configurable.

       option bcms-controller-address ip-address [, ip-address... ];

	 This option configures a list of IPv4 addresses for use as  Broadcast
	 and Multicast Controller Servers ("BCMS").

       option bcms-controller-names domain-list;

	 This  option  contains the domain names of local Broadcast and Multi‐
	 cast Controller Servers ("BCMS") controllers  which  the  client  may
	 use.

       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 capwap-ac-v4 ip-address [, ip-address ... ] ;

	 A  list  of  IPv4  addresses of CAPWAP ACs that the WTP may use.  The
	 addresses are listed in preference order.

	 This option is included based on RFC 5417.

       option client-last-transaction-time uint32;

	 This option is part of lease query.  It allows the receiver to deter‐
	 mine  the time of the most recent access by the client.  The value is
	 a duration in seconds from when the client last communicated with the
	 DHCP server.

	 This option is not user configurable.

       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 default-url string;

	 The  format  and meaning of this option is not described in any stan‐
	 dards document, but is claimed to be in use by Apple Computer.	 It is
	 not  known  what  clients  may	 reasonably  do	 if supplied with this
	 option.  Use at your own risk.

       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
		      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 uint8 [, uint8... ];

	 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 user configurable, but it will be ignored if the value
	 is greater than or equal to the lease time.

	 To make DHCPv4+DHCPv6 migration easier in the future, any value  con‐
	 figured in this option is also used as a DHCPv6 "T1" (renew) time.

       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 user configurable, but it will be ignored if the value
	 is greater than or equal to the rebinding time, or lease time.

	 To  make DHCPv4+DHCPv6 migration easier in the future, any value con‐
	 figured in this option is also used as a DHCPv6 "T2" (rebind) time.

       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 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 domain-search domain-list;

	 The domain-search option specifies a ´search list´ of Domain Names to
	 be  used  by  the  client to locate not-fully-qualified domain names.
	 The difference between this option and historic use  of  the  domain-
	 name  option  for  the	 same  ends  is that this option is encoded in
	 RFC1035 compressed labels on the wire.	 For example:

	   option domain-search "example.com", "sales.example.com",
				"eng.example.com";

       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 geoconf-civic string;

	 A string to hold the geoconf civic structure.

	 This option is included based on RFC 4776.

       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  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 name-service-search uint16 [, uint6... ];

	 This option specifies a list of name services in the order the client
	 should attempt to use them.

	 This option is included based on RFC 2937.

       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  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 netinfo-server-address ip-address [, ip-address... ];

	 The  netinfo-server-address option has not been described in any RFC,
	 but has been allocated (and is claimed to be in use) by Apple Comput‐
	 ers.	It's  hard  to say if the above is the correct format, or what
	 clients might be expected to do if values were	 configured.   Use  at
	 your own risk.

       option netinfo-server-tag text;

	 The  netinfo-server-tag option has not been described in any RFC, but
	 has been allocated (and is claimed to be in use) by Apple  Computers.
	 It's  hard to say if the above is the correct format, or what clients
	 might be expected to do if values were configured.  Use at  your  own
	 risk.

       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...  ];

	 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 servers 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
	 5905)	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 option-6rd uint8	uint8  ip6-address  ip-address	[,  ip-address
       ...];

	 This  option  contains information about the rapid deployment option.
	 It is 8 bits of ipv4 mask length, 8 bits of  6rd  prefix  length,  an
	 ipv6  prefix  as  an  ipv6  address  and  a  list of one or more ipv4
	 addresses.

	 This option is included based on RFC 5969.

       option pana-agent ip-address [, ip-address ... ] ;

	 A set of IPv4 addresses  of  a	 PAA  for  the	client	to  use.   The
	 addresses are listed in preferred order.

	 This option is included based on RFC 5192.

       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 pcode text;

	 This option specifies a string suitable for the TZ variable.

	 This option is included based on RFC 4833.

       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.

       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 rdnss-selection uint8 ip-address ip-address domain-name;

	 The rdnss-selection option specifies an 8 bit flags field, a  primary
	 and  secondary	 ip  address  for  the name server and a domainlist of
	 domains for which the RDNSS has special knowledge.

	 This option is included based on RFC 6731.

       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 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 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 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 ip-address;

	 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 tcode text;

	 This option specifies a name of a zone entry in the TZ database.

	 This option is included based on RFC 4833.

       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 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 v4-access-domain domain-name;

	 The domain name associated with the access network for use  with  LIS
	 Discovery.

	 This option is included based on RFC 5986.

       option v4-lost domain-name;

	 The domain name of the LoST server for the client to use.

	 This option is included based on RFC 5223.

       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 vivso string;

	 The vivso option can contain multiple separate options, one for  each
	 32-bit	 Enterprise  ID.  Each Enterprise-ID discriminated option then
	 contains additional options whose format is defined by the vendor who
	 holds	that  ID.  This option is usually not configured manually, but
	 rather is configured via intervening option definitions.  Please also
	 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 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 allo‐
       cation 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  informa‐
       tion 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 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-speci‐
	 fied,	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.

       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.

       option agent.link-selection ip-address;

	 The  link-selection  suboption	 is provided by relay agents to inform
	 servers what subnet the client is actually attached to.  This is use‐
	 ful  in those cases where the giaddr (where responses must be sent to
	 the relay agent) is not on the same subnet as the client.  When  this
	 option	 is  present  in  a packet from a relay agent, the DHCP server
	 will use its contents to find a subnet declared in configuration, and
	 from  here  take one step further backwards to any shared-network the
	 subnet may be defined within; the client may  be  given  any  address
	 within that shared network, as normally appropriate.

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.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 ´.´ character in the name, it is  not	 fully-qualified,  and
	 the  server  will  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 suboption -
	 for  example,	if  the value of fqdn.fqdn is "foo.example.com.", then
	 fqdn.domainname 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
	 utility uses this value as Primary DSS server when configuring a sec‐
	 ondary DSS server.

STANDARD DHCPV6 OPTIONS
       DHCPv6 options differ from DHCPv4 options partially due to using 16-bit
       code and length tags, but semantically zero-length options are legal in
       DHCPv6, and multiple  options  are  treated  differently.   Whereas  in
       DHCPv4  multiple	 options  would be concatenated to form one option, in
       DHCPv6 they are expected to be individual instantiations.   Understand‐
       ably,  many  options  are not "allowed" to have multiple instances in a
       packet - normally these are options which are digested by the DHCP pro‐
       tocol software, and not by users or applications.

       option dhcp6.client-id string;

	 This  option specifies the client's DUID identifier.  DUIDs are simi‐
	 lar but different from DHCPv4 client identifiers -  there  are	 docu‐
	 mented duid types:

	 duid-llt

	 duid-en

	 duid-ll

	 This  value  should  not  be  configured,  but	 rather is provided by
	 clients and treated as an opaque identifier key blob by servers.

       option dhcp6.server-id string;

	 This option specifies the server's DUID identifier.  One may use this
	 option	 to  configure an opaque binary blob for your server's identi‐
	 fier.

       option dhcp6.ia-na string;

	 The Identity Association for Non-temporary Addresses (ia-na)  carries
	 assigned  addresses  that  are not temporary addresses for use by the
	 DHCPv6 client.	 This option is produced by the	 DHCPv6	 server	 soft‐
	 ware, and should not be configured.

       option dhcp6.ia-ta string;

	 The Identity Association for Temporary Addresses (ia-ta) carries tem‐
	 porary addresses, which may change upon every renewal.	 There	is  no
	 support for this in the current DHCPv6 software.

       option dhcp6.ia-addr string;

	 The  Identity Association Address option is encapsulated inside ia-na
	 or ia-ta options in order  to	represent  addresses  associated  with
	 those	IA's.	These  options	are  manufactured  by the software, so
	 should not be configured.

       option dhcp6.oro uint16 [ , uint16, ... ];

	 The Option Request Option ("ORO") is the  DHCPv6  equivalent  of  the
	 parameter-request-list.  Clients supply this option to ask servers to
	 reply with options relevant to their needs and use.  This option must
	 not  be  directly configured, the request syntax in dhclient.conf (5)
	 should be used instead.

       option dhcp6.preference uint8;

	 The preference option informs a DHCPv6 client which server  is	 ´pre‐
	 ferred´  for  use on a given subnet.  This preference is only applied
	 during the initial stages of configuration - once a client  is	 bound
	 to an IA, it will remain bound to that IA until it is no longer valid
	 or has expired.  This value may be configured on the server,  and  is
	 digested by the client software.

       option dhcp6.elapsed-time uint16;

	 The elapsed-time option is constructed by the DHCPv6 client software,
	 and is potentially consumed by intermediaries.	  This	option	should
	 not be configured.

       option dhcp6.relay-msg string;

	 The relay-msg option is constructed by intervening DHCPv6 relay agent
	 software.  This option is entirely used by protocol software, and  is
	 not meant for user configuration.

       option dhcp6.unicast ip6-address;

	 The  unicast  option  is provided by DHCPv6 servers which are willing
	 (or prefer) to receive Request, Renew, Decline, and  Release  packets
	 from their clients via unicast.  Normally, DHCPv6 clients will multi‐
	 cast these messages.  Per RFC 3315, the server will reject a  unicast
	 message  received  from  a client unless it previously sent (or would
	 have sent) the unicast option to that client.	 This  option  may  be
	 configured  on	 the  server  at  the global and shared network level.
	 When a unicast message is received, the  server  will	check  for  an
	 applicable  definition	 of  the unicast option.  If such an option is
	 found the message will be accepted, if not it will be rejected.

       option dhcp6.status-code status-code [ string ] ;

	 The status-code option	 is  provided  by  DHCPv6  servers  to	inform
	 clients  of  error  conditions	 during	 protocol communication.  This
	 option is manufactured and digested by protocol software, and	should
	 not be configured.

       option dhcp6.rapid-commit ;

	 The  rapid-commit  option is a zero-length option that clients use to
	 indicate their desire to enter into rapid-commit with the server.

       option dhcp6.vendor-opts string;

	 The vendor-opts option is actually an encapsulated sub-option	space,
	 in which each Vendor-specific Information Option (VSIO) is identified
	 by a 32-bit Enterprise-ID number.   The  encapsulated	option	spaces
	 within these options are defined by the vendors.

	 To  make  use	of this option, the best way is to examine the section
	 titled VENDOR ENCAPSULATED OPTIONS  below,  in	 particular  the  bits
	 about the "vsio" option space.

       option dhcp6.interface-id string;

	 The  interface-id  option is manufactured by relay agents, and may be
	 used to guide configuration differentiating clients by the  interface
	 they are remotely attached to.	 It does not make sense to configure a
	 value for this option, but it may make sense to inspect its contents.

       option dhcp6.reconf-msg dhcpv6-message;

	 The reconf-msg option is manufactured by servers, and sent to clients
	 in  Reconfigure  messages  to	inform them of what message the client
	 should Reconfigure using.  There is no support for DHCPv6 Reconfigure
	 extensions, and this option is documented informationally only.

       option dhcp6.reconf-accept ;

	 The  reconf-accept  option is included by DHCPv6 clients that support
	 the Reconfigure extensions, advertising that they will respond if the
	 server	 were  to  ask	them  to Reconfigure.  There is no support for
	 DHCPv6 Reconfigure extensions, and this option is documented informa‐
	 tionally only.

       option dhcp6.sip-servers-names domain-list;

	 The sip-servers-names option allows SIP clients to locate a local SIP
	 server that is to be used  for	 all  outbound	SIP  requests,	a  so-
	 called"outbound  proxy	 server."  If you wish to use manually entered
	 IPv6 addresses instead, please see the	 sip-servers-addresses	option
	 below.

       option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;

	 The sip-servers-addresses option allows SIP clients to locate a local
	 SIP server that is to be used for all outbound SIP  requests,	a  so-
	 called	 "outbound  proxy  servers."   If you wish to use domain names
	 rather than IPv6 addresses, please see the  sip-servers-names	option
	 above.

       option dhcp6.name-servers ip6-address [, ip6-address ... ] ;

	 The  name-servers  option  instructs  clients about locally available
	 recursive DNS servers.	 It is easiest to describe this as the	"name‐
	 server" line in /etc/resolv.conf.

       option dhcp6.domain-search domain-list;

	 The domain-search option specifies the client's domain search path to
	 be applied to recursive DNS queries.  It is easiest to describe  this
	 as the "search" line in /etc/resolv.conf.

       option dhcp6.ia-pd string;

	 The  ia-pd  option is manufactured by clients and servers to create a
	 Prefix Delegation binding - to delegate an IPv6 prefix to the client.
	 It  is	 not directly edited in dhcpd.conf(5) or dhclient.conf(5), but
	 rather is manufactured and consumed by the software.

       option dhcp6.ia-prefix string;

	 The ia-prefix option is placed inside ia-pd options in order to iden‐
	 tify  the  prefix(es)	allocated  to  the client.  It is not directly
	 edited in dhcpd.conf(5) or dhclient.conf(5), but rather  is  manufac‐
	 tured and consumed by the software.

       option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;

	 The nis-servers option identifies, in order, NIS servers available to
	 the client.

       option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;

	 The nisp-servers option identifies, in order, NIS+ servers  available
	 to the client.

       option nis-domain-name domain-list;

	 The  nis-domain-name  option specifies the NIS domain name the client
	 is expected to use, and is related to the nis-servers option.

       option dhcp6.nis-domain-name domain-name;

	 The dhcp6.nis-domain-name option specifies NIS domain name the client
	 is expected to use, and is related to dhcp6.nis-servers option.

       option nisp-domain-name domain-list;

	 The nisp-domain-name option specifies the NIS+ domain name the client
	 is expected to use, and is related to the nisp-servers option.

       option dhcp6.nisp-domain-name domain-name;

	 The dhcp6.nis-domain-name  option  specifies  NIS+  domain  name  the
	 client	 is  expected  to  use,	 and  is related to dhcp6.nisp-servers
	 option.

       option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;

	 The sntp-servers option specifies a list of local SNTP servers avail‐
	 able for the client to synchronize their clocks.

       option dhcp6.info-refresh-time uint32;

	 The  info-refresh-time option gives DHCPv6 clients using Information-
	 request messages a hint as to how long they should between refreshing
	 the  information they were given.  Note that this option will only be
	 delivered to the client, and be likely to affect the client's	behav‐
	 iour, if the client requested the option.

       option dhcp6.bcms-server-d domain-list;

	 The  bcms-server-d  option  contains  the  domain names of local BCMS
	 (Broadcast and Multicast  Control  Services)  controllers  which  the
	 client may use.

       option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;

	 The  bcms-server-a  option  contains the IPv6 addresses of local BCMS
	 (Broadcast and Multicast  Control  Services)  controllers  which  the
	 client may use.

       option dhcp6.geoconf-civic string;

	 A string to hold the geoconf civic structure.

	 This option is included based on RFC 4776.

       option dhcp6.remote-id string;

	 The  remote-id	 option	 is constructed by relay agents, to inform the
	 server of details pertaining to what the relay knows about the client
	 (such as what port it is attached to, and so forth).  The contents of
	 this option have some vendor-specific structure  (similar  to	VSIO),
	 but we have chosen to treat this option as an opaque field.

       option dhcp6.subscriber-id string;

	 The  subscriber-id  option  is	 an opaque field provided by the relay
	 agent, which provides additional information about the subscriber  in
	 question.   The  exact contents of this option depend upon the vendor
	 and/or the operator's configuration of the remote device, and as such
	 is an opaque field.

       option dhcp6.fqdn string;

	 The  fqdn option is normally constructed by the client or server, and
	 negotiates the client's Fully Qualified Domain Name, as well as which
	 party is responsible for Dynamic DNS Updates.	See the section on the
	 Client FQDN SubOptions for full details (the DHCPv4 and  DHCPv6  FQDN
	 options  use  the same "fqdn." encapsulated space, so are in all ways
	 identical).

       option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;

	 A set of IPv6 addresses  of  a	 PAA  for  the	client	to  use.   The
	 addresses are listed in preferred order.

	 This option is included based on RFC 5192.

       option dhcp6.new-posix-timezone text;

	 This option specifies a string suitable for the TZ variable.

	 This option is included based on RFC 4833.

       option dhcp6.new-tzdb-timezone text;

	 This option specifies a name of a zone entry in the TZ database.

	 This option is included based on RFC 4833.

       option dhcp6.ero uint16 [, uint16 ... ] ;

	 A list of the options requested by the relay agent.

	 This option is included based on RFC 4994.

       option dhcp6.lq-query string;

	 The lq-query option is used internally for lease query.

       option dhcp6.client-data string;

	 The client-data option is used internally for lease query.

       option dhcp6.clt-time uint32;

	 The clt-time option is used internally for lease query.

       option dhcp6.lq-relay-data ip6-address string;

	 The lq-relay-data option is used internally for lease query.

       option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;

	 The lq-client-link option is used internally for lease query.

       option dhcp6.v6-lost domain-name;

	 The domain name of the LoST server for the client to use.

	 This option is included based on RFC 5223.

       option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;

	 A  list  of  IPv6  addresses of CAPWAP ACs that the WTP may use.  The
	 addresses are listed in preference order.

	 This option is included based on RFC 5417.

       option dhcp6.relay-id string;

	 The DUID for the relay agent.

	 This option is included based on RFC 5460.

       option dhcp6.v6-access-domain domain-name;

	 The domain name associated with the access network for use  with  LIS
	 Discovery.

	 This option is included based on RFC5986.

       option dhcp6.sip-ua-cs-list domain-list;

	 The  list of domain names in the SIP User Agent Configuration Service
	 Domains.

	 This option is included based on RFC 6011.

       option dhcp6.bootfile-url text;

	 The URL for a boot file.

	 This option is included based on RFC 5970.

       option dhcp6.bootfile-param string;

	 A string for the parameters to the bootfile.  See RFC 5970  for  more
	 description of the layout of the parameters within the string.

	 This option is included based on RFC 5970.

       option dhcp6.client-arch-type uint16 [, uint16 ... ] ;

	 A list of one or more architecture types described as 16 bit values.

	 This option is included based on RFC 5970.

       option dhcp6.nii uint8 uint8 uint8;

	 The  client  network interface identitier option supplies information
	 about a client's level of UNDI support.  The values  are,  in	order,
	 the type, the major value and the minor value.

	 This option is included based on RFC5970.

       option dhcp6.aftr-name domain-name;

	 A domain name of the AFTR tunnel endpoint.

	 This option is included based on RFC 6334.

       option dhcp6.erp-local-domain-name domain-name;

	 A domain name for the ERP domain.

	 This option is included based on RFC 6440.

       option dhcp6.rdnss-selection ip6-address uint8 domain-name;

	 RDNSS	information  consists  of  an  IPv6 address of RDNSS, an 8 bit
	 flags field and a domain-list of domains for which the RDNSS has spe‐
	 cial knowledge.

	 This option is included based on RFC 6731.

       option dhcp6.client-linklayer-addr string;

	 A client link-layer address.  The first two bytes must be the type of
	 the link-layer followed by the address itself.

	 This option is included based on RFC 6939.

       option dhcp6.link-address ip6-address;

	 An IPv6 address used by a relay agent to indicate to the  server  the
	 link on which the client is located.

	 This option is included based on RFC 6977.

       option dhcp6.solmax-rt uint32;

	 A  value  to  override	 the default for SOL_MAX_RT.  This is a 32 bit
	 value.

	 This option is included based on RFC 7083.

       option dhcp6.inf-max-rt uint32;

	 A value to override the default for INF_MAX_RT.  This	is  a  32  bit
	 value.

	 This option is included based on RFC 7083.

ACCESSING DHCPV6 RELAY OPTIONS
       v6relay	(relay-number,	option) This option allows access to an option
       that has been added to a packet by a relay agent.   Relay-number	 value
       selects	the  relay  to	examine	 and option is the option to find.  In
       DHCPv6 each relay encapsulates the  entire  previous  message  into  an
       option,	adds  its  own	options (if any) and sends the result onwards.
       The RFC specifies a limit of 32 hops.  A relay-number of 0 is  a	 no-op
       and  means don't look at the relays.  1 is the relay that is closest to
       the client, 2 would be the next in from the  client  and	 so  on.   Any
       value  greater  than  the max number of hops is which is closest to the
       server independent of number.  To use this option in a class  statement
       you would have something like this:

       match if v6relay(1, option dhcp6.subscriber-id) = "client_1";

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.  All codes between
       224  and 254 are reserved as ´site-local´ DHCP options, so you can pick
       any one of these for your site (not for your product/application).   In
       RFC3942, site-local space was moved from starting at 128 to starting at
       224.  In practice, some vendors have interpreted	 the  protocol	rather
       loosely	and  have used option code values greater than 128 themselves.
       There's no real way to avoid this problem, and it  was  thought	to  be
       unlikely	 to  cause too much trouble in practice.  If you come across a
       vendor-documented option code in either the new or old site-local  spa‐
       ces, please contact your vendor and inform them about rfc3942.

       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;

       IP6-ADDRESS

       option new-name code new-code = ip6-address ;

       An  option  whose  structure  is an IPv6 address must be expressed as a
       valid IPv6 address.  The following is an example use of the ip6-address
       type:

       option dhcp6.some-server code 1234 = array of ip6-address;
       option dhcp6.some-server 3ffe:bbbb:aaaa:aaaa::1, 3ffe:bbbb:aaaa:aaaa::2;

       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;

       DOMAIN-LIST

       option new-name code new-code = domain-list [compressed] ;

       An  option  whose  type	is domain-list is an RFC1035 formatted (on the
       wire, "DNS Format") list of domain names,  separated  by	 root  labels.
       The  optional compressed keyword indicates if the option should be com‐
       pressed relative to the start of the option contents  (not  the	packet
       contents).

       When in doubt, omit the compressed keyword.  When the software receives
       an option that is compressed and the compressed keyword is omitted,  it
       will  still  decompress	the  option  (relative	to the option contents
       field).	The keyword only controls whether or not  transmitted  packets
       are compressed.

       Note  that when domain-list formatted options are output as environment
       variables to dhclient-script(8), the standard DNS -escape mechanism  is
       used:  they  are	 decimal.   This  is  appropriate for direct use in eg
       /etc/resolv.conf.

       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 encapsu‐
       lated in a standard DHCP option.	 It also defines the Vendor Identified
       Vendor  Sub  Options  option ("VIVSO"), and the DHCPv6 protocol defines
       the Vendor-specific Information Option ("VSIO").	 The format of all  of
       these  options  is usually internally a string of options, similarly to
       other normal DHCP options.  The VIVSO and VSIO options differ  in  that
       they  contain  options  that correspond to vendor Enterprise-ID numbers
       (assigned by IANA), which then contain options according to  each  Ven‐
       dor's specifications.  You will need to refer to your vendor's documen‐
       tation in order to form options to their specification.

       The value of these options 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 help in forming	 these
       strings,	 please refer to RFC2132 for the DHCPv4 Vendor Specific Infor‐
       mation Option, RFC3925 for the  DHCPv4  Vendor  Identified  Vendor  Sub
       Options,	 or RFC3315 for the DHCPv6 Vendor-specific Information Option.
       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;
       option vivso
	   00:00:09:bf:0E:
	    01:0c:
		48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
       option dhcp6.vendor-opts
	   00:00:09:bf:
	    00:01:00:0c:
		48:65:6c:6c:6f:20:77:6f:72:6c:64:21;

       The second way of setting the value of these options  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 relevant option.

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

       option  space  name  [  [ code width number ] [ length width number ] [
       hash size number ] ] ;

       Where the numbers following code width, length  width,  and  hash  size
       respectively  identify  the  number  of	bytes  used to describe option
       codes, option lengths, and the size in buckets of the  hash  tables  to
       hold  options in this space (most DHCPv4 option spaces use 1 byte codes
       and lengths, which is the default, whereas most	DHCPv6	option	spaces
       use 2 byte codes and lengths).

       The code and length widths are used in DHCP protocol - you must config‐
       ure these numbers to match the applicable option space you are  config‐
       uring.	They each default to 1.	 Valid values for code widths are 1, 2
       or 4.  Valid values for length widths are  0,  1	 or  2.	  Most	DHCPv4
       option  spaces  use  1  byte  codes  and lengths, which is the default,
       whereas most DHCPv6 option spaces use 2	byte  codes  and  lengths.   A
       zero-byte length produces options similar to the DHCPv6 Vendor-specific
       Information Option - but not their contents!

       The hash size defaults depend upon the code width selected, and may  be
       254  or	1009.	Valid values range between 1 and 65535.	 Note that the
       higher you configure this value, the more memory will be used.	It  is
       considered  good	 practice to configure a value that is slightly larger
       than the estimated number of options you plan to configure  within  the
       space.  Previous versions of ISC DHCP (up to and including DHCP 3.0.*),
       this value was fixed at 9973.

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

       option space SUNW code width 1 length width 1 hash size 3;
       option SUNW.server-address code 2 = ip-address;
       option SUNW.server-name code 3 = text;
       option SUNW.root-path code 4 = text;

       option space ISC code width 1 length width 1 hash size 3;
       option ISC.sample code 1 = text;
       option vendor.ISC code 2495 = encapsulate vivso-sample;
       option vendor-class.ISC code 2495 = text;

       option ISC.sample "configuration text here";
       option vendor-class.ISC "vendor class here";

       option space docsis code width 2 length width 2 hash size 17;
       option docsis.tftp-servers code 32 = array of ip6-address;
       option docsis.cablelabs-configuration-file code 33 = text;
       option docsis.cablelabs-syslog-servers code 34 = array of ip6-address;
       option docsis.device-id code 36 = string;
       option docsis.time-servers code 37 = array of ip6-address;
       option docsis.time-offset code 38 = signed integer 32;
       option vsio.docsis code 4491 = encapsulate docsis;

       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 dif‐
       ferent classes of clients.  Using the option space definition shown  in
       the previous example, you can send different option values to different
       clients based on the vendor-class-identifier option  that  the  clients
       send, as follows:

       class "vendor-classes" {
	 match option vendor-class-identifier;
       }

       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";
       }

       option SUNW.server-address 172.17.65.1;
       option SUNW.server-name "sundhcp-server17-1";

       option vivso-sample.sample "Hello world!";

       option docsis.tftp-servers ::1;

       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 DHCPv4 vendor-
       encapsulated-options option.  This is a limitation of that option - the
       DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi‐
       nitions all at once (even transmitted to the same client), so it is not
       necessary to configure this.

SEE ALSO
       dhcpd.conf(5),	 dhcpd.leases(5),    dhclient.conf(5),	 dhcp-eval(5),
       dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.

AUTHOR
       Information  about  Internet  Systems  Consortium  can  be   found   at
       https://www.isc.org.

							       dhcp-options(5)
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