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Linux 2.6 - man page for dhcp-options (linux section 5)

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., haagen.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  inte-
       gers.  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 existing 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.example.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, separated 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 eval-
       uation 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 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 exam-
       ple in conditional 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 configurable"

       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 sub-
	 nets 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 Con-
	 troller Servers ("BCMS").

       option bcms-controller-names domain-list;

	 This option contains the domain  names  of  local  Broadcast  and  Multicast  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 declaration.  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 section 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 preference.

       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 seg-
	 ments.  The minimum value is 1.

       option default-url string;

	 The format and meaning of this option is not described in any standards 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  con-
	 tained 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 over-
	 loaded 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 additional 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  nor-
	 mally	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  sev-
	 eral 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-identifier 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 available 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 preference.

       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 for-
	 warding.  A value of false means disable IP forwarding, 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 preference.

       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  allo-
	 cated	(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  config-
	 ured.	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 preference.

       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 preference.

       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 forward-
	 ing 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 NetWare/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 discov-
	 ered 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  discov-
	 ery.  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 preference.

       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  per-
	 form router discovery.

       option router-solicitation-address ip-address;

	 This  option  specifies the address to which the client should transmit router solicita-
	 tion 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 preference.

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

	 This  option specifies two things: the IP addresses of one or more Service Location Pro-
	 tocol Directory Agents, and whether the use of these addresses is  mandatory.	  If  the
	 initial  boolean  value  is  true, the SLP agent should just use the IP addresses given.
	 If the value is false, the SLP agent may additionally do  active  or  passive	multicast
	 discovery of SLP agents (see RFC2165 for details).

	 Please  note  that in this option and the slp-service-scope option, the term "SLP Agent"
	 is being used to refer to a Service Location Protocol agent running on a machine that is
	 being configured using the DHCP protocol.

	 Also,	please	be aware that some companies may refer to SLP as NDS.  If you have an NDS
	 directory agent whose address you need  to  configure,  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 ser-
	 vice 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 destination are specified, they are
	 listed in descending order of priority.

	 The routes consist of a list of IP address pairs.  The first address is the  destination
	 address, and the second address is the router for the destination.

	 The  default  route  (0.0.0.0) is an illegal destination for a static route.  To specify
	 the default route, use the routers option.   Also, please note that this option  is  not
	 intended for classless IP routing - it does not include a subnet mask.   Since classless
	 IP routing is now the most widely deployed routing standard, this  option  is	virtually
	 useless,  and is not implemented by any of the popular DHCP clients, for example the Mi-
	 crosoft 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 preference.

       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 declaration 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 declaration.   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 Coor-
	 dinated 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 preference.

       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 trailers.  A value  of  true  means	that  the  client  should
	 attempt to use trailers.

       option uap-servers text;

	 This  option  specifies  a  list of URLs, each pointing to a user authentication service
	 that is capable of processing authentication requests encapsulated in the User Authenti-
	 cation 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 component, 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 specify identifying
	 information to the client.   This can be used in a similar way to the vendor-class-iden-
	 tifier  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 configu-
	 ration 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 configuration file - instead, a vendor class is defined for each vendor,
	 vendor class suboptions are defined, values for those suboptions are  defined,  and  the
	 DHCP server makes up a response on that basis.

	 Some  default	behaviours  for  well-known DHCP client vendors (currently, the Microsoft
	 Windows 2000 DHCP client) are configured automatically, but otherwise this must be  con-
	 figured 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 for-
	 mat 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 prefer-
	 ence.

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
       permissible.   These options are not supported in the client.

       option agent.circuit-id string;

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

       option agent.remote-id string;

	 The  remote-id  suboption  encodes  information  about the remote host end of a circuit.
	 Examples of what it might contain include caller ID information,  username  information,
	 remote  ATM  address, cable modem ID, and similar things.   In principal, the meaning is
	 not well-specified, and it should generally be assumed to be an opaque  object  that  is
	 administratively guaranteed to be unique to a 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 end-
	 point, 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 imple-
	 mented 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 useful 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 sufficiently wide use already that we  have
       implemented  it.   Due to the complexity of the option format, we have implemented it as a
       suboption space rather than a single option.   In general this option should not  be  con-
       figured 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  configu-
	 ration side, it controls the format in which the fqdn.fqdn suboption is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

	 These	options specify the result of the updates of the A and PTR records, respectively,
	 and are only sent by the DHCP server to the DHCP client.  The values of these fields are
	 those defined in the DNS protocol specification.

       option fqdn.fqdn text;

	 Specifies the domain name that the client wishes to use.   This can be a fully-qualified
	 domain name, or a single label.   If there is no trailing '.' 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.exam-
	 ple.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 comparison, 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 secondary 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.  Understandably, many
       options are not "allowed" to have multiple instances in a  packet  -  normally  these  are
       options	which  are  digested  by the DHCP protocol software, and not by users or applica-
       tions.

       option dhcp6.client-id string;

	 This option specifies the client's DUID identifier.  DUIDs  are  similar  but	different
	 from DHCPv4 client identifiers - there are documented 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  config-
	 ure an opaque binary blob for your server's identifier.

       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 software, and should not be configured.

       option dhcp6.ia-ta string;

	 The  Identity	Association  for Temporary Addresses (ia-ta) carries temporary 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 'preferred' for use  on	a
	 given	subnet.   This preference is only applied during the initial stages of configura-
	 tion - 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.  Nor-
	 mally, 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 condi-
	 tions during protocol communication.  This option is manufactured and digested by proto-
	 col 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 con-
	 figured.

       option dhcp6.vendor-opts string;

	 The vendor-opts option is actually an encapsulated sub-option space, in which each  Ven-
	 dor-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  ENCAP-
	 SULATED 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 con-
	 figuration 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 information-
	 ally 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  Recon-
	 figure.  There is no support for DHCPv6 Reconfigure extensions, and this option is docu-
	 mented informationally 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 "nameserver" 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 identify 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 available 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 behaviour, 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 Multi-
	 cast 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 Multi-
	 cast 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 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 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  con-
       tents 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 compressed 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  trans-
       mitted 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 encapsulated 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  corre-
       spond  to  vendor  Enterprise-ID  numbers  (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 Information 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 configure these numbers to
       match the applicable option space you are configuring.  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.  Pre-
       vious 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 exam-
       ple, 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  differ-
       ent 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-encapsu-
       lated-options  option.	This  is  a  limitation of that option - the DHCPv4 VIVSO and the
       DHCPv6 VSIO options can have multiple vendor definitions 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  con-
       tract  with  Vixie  Labs.   Funding for this project was provided through Internet Systems
       Consortium.   Information  about   Internet   Systems   Consortium   can   be   found   at
       https://www.isc.org.

										 dhcpd-options(5)


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