dhcpd-options(5) dhcpd-options(5)

NAME dhcp-options - Dynamic Host Configuration Protocol options

DESCRIPTION The Dynamic Host Configuration protocol allows the client to receive options from the DHCP server describing the network configuration and various services that are available on the network. When configuring dhcpd(8) or dhclient(8) , options must often be declared. The syntax for declaring options, and the names and formats of the options that can be declared, are documented here.

REFERENCE: OPTION STATEMENTS DHCP option statements always start with the option keyword, followed by an option name, followed by option data. The option names and data formats are described below. It is not necessary to exhaustively specify all DHCP options - only those options which are needed by clients must be specified.

   Option data comes in a variety of formats, as defined below:

   The ip-address data type can  be	 entered  either  as  an  explicit  IP
   address	(e.g.,	239.254.197.10)	 or  as	 a  domain  name  (e.g.,  haa-
   gen.isc.org).  When entering a domain name, be sure  that  that	domain
   name resolves to a single IP address.

   The   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.   This data type is not used for any exist-
   ing DHCP options.   The domain name is stored just as if it were a text
   option.

   The 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));

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 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 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 uint16 [, uint16... ];

 This option, when sent by the client,	specifies  which  options  the
 client	 wishes	 the  server  to  return.    Normally, in the ISC DHCP
 client, this is done using the request statement.   If this option is
 not  specified	 by  the  client, the DHCP server will normally return
 every option that is valid in scope and that  fits  into  the	reply.
 When  this  option is specified on the server, the server returns the
 specified options.   This can be used	to  force  a  client  to  take
 options  that	it hasn't requested, and it can also be used to tailor
 the response of the DHCP server for clients that may need a more lim-
 ited set of options than those the server would normally return.

   option dhcp-rebinding-time uint32;

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

 This option is not user configurable.

   option dhcp-renewal-time uint32;

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

 This option is not user configurable.

   option dhcp-requested-address ip-address;

 This option is used by the client in a DHCPDISCOVER to request that a
 particular IP address be assigned.

 This option is not user configurable.

   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 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 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 servesr available to
 the client.  Servers should be listed in order of preference.

   option non-local-source-routing flag;

 This option specifies whether the  client  should  configure  its  IP
 layer	to  allow forwarding of datagrams with non-local source routes
 (see Section 3.3.5 of [4] for a discussion of this topic).   A	 value
 of  false means disallow forwarding of such datagrams, and a value of
 true means allow forwarding.

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

 This option specifies a list of  IP  addresses	 indicating  NTP  (RFC
 1035)	servers	 available to the client.  Servers should be listed in
 order of preference.

   option nwip-domain string;

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

   option nwip-suboptions string;

 A  sequence  of  suboptions  for NetWare/IP clients - see RFC2242 for
 details.   Normally this option is set by  specifying	specific  Net-
 Ware/IP  suboptions  - see the NETWARE/IP SUBOPTIONS section for more
 information.

   option path-mtu-aging-timeout uint32;

 This option specifies the timeout (in seconds) to use when aging Path
 MTU values discovered by the mechanism defined in RFC 1191.

   option path-mtu-plateau-table uint16 [, uint16...  ];

 This  option  specifies  a  table of MTU sizes to use when performing
 Path MTU Discovery as defined in RFC 1191.  The table is formatted as
 a list of 16-bit unsigned integers, ordered from smallest to largest.
 The minimum MTU value cannot be smaller than 68.

   option perform-mask-discovery flag;

 This option specifies whether or not the client should perform 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 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 string;

 Sent by the client if an address is required in a subnet  other  than
 the  one  that	 would	normally  be  selected	(based on the relaying
 address of the connected subnet the request is	 obtained  from).  See
 RFC3011. Note that the option number used by this server is 118; this
 has not always been the defined number, and some clients  may	use  a
 different  value.  Use	 of this option should be regarded as slightly
 experimental!

   This option is not user configurable in the server.

   option swap-server ip-address;

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

   option tcp-keepalive-garbage flag;

 This option specifies whether or  not	the  client  should  send  TCP
 keepalive  messages  with  an octet of garbage for compatibility with
 older implementations.	 A value of false  indicates  that  a  garbage
 octet	should	not  be sent. A value of true indicates that a garbage
 octet should be sent.

   option tcp-keepalive-interval uint32;

 This option specifies the interval (in seconds) that the  client  TCP
 should	 wait  before sending a keepalive message on a TCP connection.
 The time is specified as a 32-bit unsigned integer.  A value of  zero
 indicates  that  the client should not generate keepalive messages on
 connections unless specifically requested by an application.

   option tftp-server-name text;

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

   option time-offset int32;

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

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

 The time-server option specifies a  list  of  RFC  868	 time  servers
 available  to the client.  Servers should be listed in order of pref-
 erence.

   option trailer-encapsulation flag;

 This option specifies whether or not the client should negotiate  the
 use  of trailers (RFC 893 [14]) when using the ARP protocol.  A value
 of false indicates that the client should not attempt to  use	trail-
 ers.	A  value  of  true means that the client should attempt to use
 trailers.

   option uap-servers text;

 This option specifies a list of URLs, each pointing to a user authen-
 tication   service  that  is  capable	of  processing	authentication
 requests encapsulated in the User Authentication Protocol (UAP).  UAP
 servers can accept either HTTP 1.1 or SSLv3 connections.  If the list
 includes a URL that does not contain a	 port  component,  the	normal
 default  port	is  assumed  (i.e.,  port 80 for http and port 443 for
 https).  If the list includes a URL that does not contain a path com-
 ponent, the path /uap is assumed.   If more than one URL is specified
 in this list, the URLs are separated by spaces.

   option user-class string;

 This option is used by some DHCP clients as a way for users to	 spec-
 ify  identifying  information	to the client.	 This can be used in a
 similar way to the vendor-class-identifier option, but the  value  of
 the  option  is  specified by the user, not the vendor.   Most recent
 DHCP clients have a way in the user interface to  specify  the	 value
 for this identifier, usually as a text string.

   option vendor-class-identifier string;

 This  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 allocation decisions (or whatever other decisions it wants) based on these options. The server also returns these options in any replies it sends through the relay agent, so that the relay agent can use the information in these options for delivery or accounting purposes.

   The  current draft defines two options.	 To reference these options in
   the dhcp server, specify the option space name, "agent", followed by  a
   period,	followed  by  the  option name.	  It is not normally useful to
   define values for these options in the server, although it is permissi-
   ble.   These options are not supported in the client.

   option agent.circuit-id string;

 The  circuit-id  suboption  encodes  an agent-local identifier of the
 circuit from which a DHCP client-to-server packet was	received.   It
 is  intended for use by agents in relaying DHCP responses back to the
 proper circuit.   The format of this option is currently  defined  to
 be  vendor-dependent, and will probably remain that way, although the
 current draft allows for for the  possibility	of  standardizing  the
 format in the future.

   option agent.remote-id string;

 The remote-id suboption encodes information about the remote host end
 of a circuit.	 Examples of what it might contain include  caller  ID
 information,  username	 information,  remote ATM address, cable modem
 ID, and similar things.   In principal, the meaning is not well-spec-
 ified, and it should generally be assumed to be an opaque object that
 is administratively guaranteed to be unique to	 a  particular	remote
 end of a circuit.

   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 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.hostname will be "example.com.".	 If this  suboption  value  is
 not  set,  it	means  that  an	 unqualified name was sent in the fqdn
 option, or that no fqdn option was sent at all.

   If you wish to use any of these suboptions, we strongly recommend  that
   you refer to the Client FQDN option draft (or standard, when it becomes
   a standard) - the documentation here is sketchy and incomplete in  com-
   parison,	 and  is  just	intended  for  reference by people who already
   understand the Client FQDN option specification.

THE NETWARE/IP SUBOPTIONS RFC2242 defines a set of encapsulated options for Novell NetWare/IP clients. To use these options in the dhcp server, specify the option space name, “nwip”, followed by a period, followed by the option name. The following options can be specified:

   option nwip.nsq-broadcast flag;

 If  true,  the	 client should use the NetWare Nearest Server Query to
 locate a NetWare/IP server.   The behaviour of the Novell  client  if
 this suboption is false, or is not present, is not specified.

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

 This  suboption  specifies a list of up to five IP addresses, each of
 which should be the IP address of a  NetWare  Domain  SAP/RIP	server
 (DSS).

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

 This  suboption  specifies a list of up to five IP addresses, each of
 which should be the IP address of a Nearest NetWare IP server.

   option nwip.autoretries uint8;

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

   option nwip.autoretry-secs uint8;

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

   option nwip.nwip-1-1 uint8;

 If  true, the NetWare/IP client should support NetWare/IP version 1.1
 compatibility.	  This is only needed if the client will be contacting
 Netware/IP version 1.1 servers.

   option nwip.primary-dss ip-address;

 Specifies the IP address of the Primary Domain SAP/RIP Service server
 (DSS) for this NetWare/IP  domain.    The  NetWare/IP	administration
 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 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 Renew packets from their clients by exchanging
 UDP unicasts with them.   Normally,  DHCPv6  clients  will  multicast
 their	Renew  messages.   This	 may  be configured on the server, and
 should be configured as an address the server is ready to reply to.

   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.
 This  option  is  not	supported  by  the client at this time, and is
 digested by the server when present, so should not be configured.

   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 extentions, 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.
 There	is not yet any support for prefix delegation in this software,
 and this option is provided informationally only.

   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.  There is not yet any
 suport for prefix delegation in this software,	 and  this  option  is
 provided informationally only.

   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 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.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.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;

 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.lq-query string;

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

   option dhcp6.client-data string;

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

   option dhcp6.clt-time uint32;

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

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

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

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

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

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 recieves
   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 that they contain options that correspond to vendor Enterprise-ID num- bers (assigned by IANA), which then contain options according to each Vendor’s specifications. You will need to refer to your vendor’s docu- mentation 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
   different classes of clients.   Using the option space definition shown
   in  the	previous example, you can send different option values to dif-
   ferent clients based on the  vendor-class-identifier  option  that  the
   clients send, as follows:

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

   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 The Internet Systems Consortium DHCP Distribution was written by Ted Lemon under a contract with Vixie Labs. Funding for this project was provided through Internet Systems Consortium. Information about Inter- net Systems Consortium can be found at https://www.isc.org.

						      dhcpd-options(5)