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dhcp-options(5)		      File Formats Manual	       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 ad-
       dress  (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.  Additionally,  please  note  the
       software	 (dhcpd	 or  dhclient) will only attempt to resolve the	domain
       name the	first time the option is needed. For  example,	if  the	 next-
       server  option  is  defined as a	domain name, dhcpd will	attempt	to re-
       solve it	while responding to the	first client query dhcpd receives  af-
       ter startup. Should the domain's	address	subsequently change, the soft-
       ware has	to be restarted	in order to pick up the	change.

       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 en-
       closed 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  op-
       tion you	would edit the includes/site.h file and	comment	out the	defin-
       ition 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 be-
       low  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 information.

       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 de-
       termined	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  di-
	 rectly	 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 ad-
	 dresses 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  op-
	 tion.	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  op-
	 tion, 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 di-
	 rectly	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  ex-
	 ceed 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  op-
	 tion 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 op-
	 tions that it hasn't requested, and it	can also be used to tailor the
	 response of the DHCP server for clients that may need a more  limited
	 set of	options	than those the server would normally return.

       option dhcp-rebinding-time uint32;

	 This  option  specifies  the number of	seconds	from the time a	client
	 gets an address until the client transitions to the REBINDING state.

	 This option is	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 re-
	 solving 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 op-
	 tions to be interpreted according to the DHCP option format as	speci-
	 fied 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 in-
	 terface 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 loader-configfile	text

	 This option is	used to	specify	a boot loading	configuration  file  a
	 PXE client should use.

	 This option is	included based on RFC 5071.

       option loader-pathprefix	text

	 This  option is used to specify a path	prefix a PXE client should use
	 in conjunction	with the boot load configuration file.

	 This option is	included based on RFC 5071.

       option loader-reboottime	uint32

	 This option is	used to	dictate	the  maximum  amount  of  time	a  PXE
	 client	 should	 allow	itself to achieve configured network resources
	 before	rebooting.

	 This option is	included based on RFC 5071.

       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  or-
	 der  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  Di-
	 rectory 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  pa-
	 rameter  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 In-
	 formation 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 do-
	 main 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 de-
	 tails.	 Normally this option is set by	specifying specific NetWare/IP
	 suboptions - see the NETWARE/IP SUBOPTIONS section for	more  informa-
	 tion.

       option pxe-system-type uint16 [,	uint16 ... ];

	 A list	of one ore more	16-bit integers	which allows a client to spec-
	 ify its pre-boot architecture type(s).

	 This option is	included based on RFC 4578.

       option pxe-interface-id uint8 uint8 uint8

	 A  three octet	value which allows a client to specify its network in-
	 terface type.

	 This option is	included based on RFC 4578.

       option pxe-client-id uint8 string

	 A single octet	indicating type, followed by a string  that  allows  a
	 client	to specify its PXE client identity.

	 This option is	included based on RFC 4578.

       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  ad-
	 dresses.

	 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 ad-
	 dresses 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  do-
	 mains 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 ad-
	 dress 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 tftp-server-address ip-address [,	ip-address... ];

	 This  option  configures a list of one	or more	IPv4 addresses of tftp
	 servers a client may use.

	 This option is	included based on RFC 5859

       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 re-
	 quests	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 de-
	 fault	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 v6-only-preferred	uint32;

	 The number of seconds the client should disable DHCPv4	for.

	 This option and its use by the	client are specified in	RFC 8925.

       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-en-
	 capsulated-options option.  Please see	the  VENDOR  ENCAPSULATED  OP-
	 TIONS 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 de-
	 fined,	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 de-
	 tails.

       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  de-
       fine  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 au-
       tomatic 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  op-
	 tion, 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 un-
       derstand	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 pa-
	 rameter-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  ap-
	 plicable  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 op-
	 tion 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 re-
	 cursive  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  op-
	 tion.

       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  ad-
	 dresses 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 ad-
	 dresses 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 op-
       tion, 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  ca-
       pability	 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 op-
       tion.   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"  be-
       cause  the  DHCP	 protocol already defines a host-name option, which is
       documented earlier in this manual page.	If an option name doesn't  ap-
       pear 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  de-
       fine  an	option,	"local-host-name", feeling some	confidence that	no of-
       ficial 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 un-
       likely to cause too much	trouble	in practice.  If  you  come  across  a
       vendor-documented  option  code	in  either  the	 new or	old site-local
       spaces, 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 in-
       teger.  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 ex-
       ample:

       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 op-
       tions in	the DHCP protocol as it	currently exists include  the  vendor-
       encapsulated-options  option, the netware-suboptions option and the re-
       lay-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  ex-
       ample:

       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  Op-
       tions,  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 op-
       tion 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 re-
       spectively  identify the	number of bytes	used to	describe option	codes,
       option lengths, and the size in buckets of the hash tables to hold  op-
       tions  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 op-
       tion 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 Informa-
       tion 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-en-
       capsulated-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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