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NetBSD 6.1.5 - man page for dhcp-options (netbsd 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 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  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 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 DHCP OPTIONS
       The  documentation  for	the various options mentioned below is taken from the latest IETF
       draft document on DHCP options.	Options not listed below may not yet be implemented,  but
       it is possible to use such options by defining them in the configuration file.  Please see
       the DEFINING NEW OPTIONS heading later in this document for more 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 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 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;

	 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 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 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
	    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 infor-
	    mation.

	 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 speci-
	    fied 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
	    configured manually - see the VENDOR ENCAPSULATED OPTIONS section later in this  man-
	    ual page for details.

	 option www-server ip-address [, ip-address... ];

	    The  WWW  server  option  specifies  a  list  of WWW servers available to the client.
	    Servers should be listed in order of preference.

	 option x-display-manager ip-address [, ip-address...  ];

	    This option specifies a list of systems that are running the X Window System  Display
	    Manager  and  are  available  to  the client.  Addresses should be listed in order of
	    preference.

RELAY AGENT INFORMATION OPTION
       An IETF draft,  draft-ietf-dhc-agent-options-11.txt,  defines  a  series  of  encapsulated
       options	that  a relay agent can add to a DHCP packet when relaying it to the DHCP server.
       The server can then make address allocation decisions  (or  whatever  other  decisions  it
       wants)  based  on these options.   The server also returns these options in any replies it
       sends through the relay agent, so that the relay agent can use the  information	in  these
       options for delivery or accounting purposes.

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

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 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.

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.	For site-local options, all codes
       between 128 and 254 are reserved for DHCP options, so you can pick any one of  these.   In
       practice,  some	vendors have interpreted the protocol rather loosely and have used option
       code values greater than 128 themselves.   There's no real way to avoid this problem,  but
       it's not likely to cause too much trouble in practice.

       The  structure  of  an option is simply the format in which the option data appears.   The
       ISC DHCP server currently supports a few simple types, like  integers,  booleans,  strings
       and  IP	addresses,  and  it also supports the ability to define arrays of single types or
       arrays of fixed sequences of types.

       New options are declared as follows:

       option new-name code new-code = definition ;

       The values of new-name and new-code should be the name you have chosen for the new  option
       and  the  code you have chosen.	 The definition should be the definition of the structure
       of the option.

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

       An option of type boolean is a flag with a value of either on or off (or true  or  false).
       So an example use of the boolean type would be:

       option use-zephyr code 180 = boolean;
       option use-zephyr on;

       INTEGER

       option new-name code new-code = sign integer width ;

       The sign token should either be blank, unsigned or signed.   The width can be either 8, 16
       or 32, and refers to the number of bits in the integer.	 So for  example,  the	following
       two lines show a definition of the sql-connection-max option and its use:

       option sql-connection-max code 192 = unsigned integer 16;
       option sql-connection-max 1536;

       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;

       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;

       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.   The
       format of the vendor-encapsulated-options option is either a series of bytes whose  format
       is  not	specified, or a sequence of options, each of which consists of a single-byte ven-
       dor-specific option code, followed by a single-byte length, followed by as many	bytes  of
       data  as  are  specified  in  the length (the length does not include itself or the option
       code).

       The value of this option can be set in one of two ways.	 The first way is to simply spec-
       ify  the  data directly, using a text string or a colon-separated list of hexadecimal val-
       ues.   For example:

       option vendor-encapsulated-options
	   2:4:AC:11:41:1:
	   3:12:73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
	   4:12:2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;

       The second way of setting the value of this option is to have the DHCP server  generate	a
       vendor-specific	option	buffer.    To  do this, you must do four things: define an option
       space, define some options in that option space, provide values for them, and specify that
       that option space should be used to generate the vendor-encapsulated-options option.

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

       option space name ;

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

       option space SUNW;
       option SUNW.server-address code 2 = ip-address;
       option SUNW.server-name code 3 = text;
       option SUNW.root-path code 4 = text;

       Once  you  have	defined  an  option  space and the format of some options, you can set up
       scopes that define values for those options, and you can say when to use them.	For 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;
       }

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

       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";
       }

       As  you	can  see in the preceding example, regular scoping rules apply, so you can define
       values that are global in the global scope, and only define values that are specific to	a
       particular  class in the local scope.   The vendor-option-space declaration tells the DHCP
       server to use options in the SUNW  option  space  to  construct	the  vendor-encapsulated-
       options option.

SEE ALSO
       dhcpd.conf(5),  dhcpd.leases(5),  dhclient.conf(5),  dhcp-eval(5),  dhcpd(8), dhclient(8),
       RFC2132, RFC2131, draft-ietf-dhc-agent-options-??.txt.

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
       http://www.isc.org.

										 dhcpd-options(5)


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