dhcp-options

dhcp-options(5)               File Formats Manual              dhcp-options(5)

NAME
       dhcp-options - Dynamic Host Configuration Protocol options

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

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

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

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

       The   ip6-address   data   specifies  an  IPv6  address,  like  ::1  or
       3ffe:bbbb:aaaa:aaaa::1.

       The int32 data type specifies a signed 32-bit integer.  The uint32 data
       type  specifies  an unsigned 32-bit integer.  The int16 and uint16 data
       types specify signed and unsigned 16-bit integers.  The int8 and  uint8
       data  types specify signed and unsigned 8-bit integers.  Unsigned 8-bit
       integers are also sometimes referred to as octets.

       The text data type specifies an NVT ASCII string,  which  must  be  en-
       closed  in  double quotes - for example, to specify a root-path option,
       the syntax would be

       option root-path "10.0.1.4:/var/tmp/rootfs";

       The domain-name data type specifies a domain name, which  must  not  be
       enclosed  in  double  quotes.   The domain name is stored just as if it
       were a text option.

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

       The flag data type specifies a boolean value.  Booleans can  be  either
       true or false (or on or off, if that makes more sense to you).

       The  string  data type specifies either an NVT ASCII string enclosed in
       double quotes, or a series of octets specified  in  hexadecimal,  sepa-
       rated by colons.  For example:

         option dhcp-client-identifier "CLIENT-FOO";
       or
         option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f;

SETTING OPTION VALUES USING EXPRESSIONS
       Sometimes  it's  helpful  to  be able to set the value of a DHCP option
       based on some value that the client has sent.  To do this, you can  use
       expression  evaluation.   The dhcp-eval(5) manual page describes how to
       write expressions.  To assign the result of an evaluation to an option,
       define the option as follows:

         option my-option = expression ;

       For example:

         option hostname = binary-to-ascii (16, 8, "-",
                                            substring (hardware, 1, 6));

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

       By default all of the options are enabled.  In order to disable an  op-
       tion  you would edit the includes/site.h file and comment out the defi-
       nition for the proper RFC.

STANDARD DHCPV4 OPTIONS
       The documentation for the various options mentioned below is taken from
       the latest IETF draft document on DHCP options.  Options not listed be-
       low may not yet be implemented, but it is possible to use such  options
       by  defining  them  in the configuration file.  Please see the DEFINING
       NEW OPTIONS heading later in this document for more information.

       Some of the options documented here are automatically generated by  the
       DHCP  server  or by clients, and cannot be configured by the user.  The
       value of such an option can be used in the configuration  file  of  the
       receiving DHCP protocol agent (server or client), for example in condi-
       tional expressions. However, the value of the option cannot be used  in
       the  configuration  file of the sending agent, because the value is de-
       termined only after the configuration file has been processed.  In  the
       following  documentation,  such options will be shown as "not user con-
       figurable"

       The standard options are:

       option all-subnets-local flag;

         This option specifies whether or not the client may assume  that  all
         subnets  of  the  IP network to which the client is connected use the
         same MTU as the subnet of that network to which  the  client  is  di-
         rectly  connected.   A value of true indicates that all subnets share
         the same MTU.  A value of false means that the client  should  assume
         that  some subnets of the directly connected network may have smaller
         MTUs.

       option arp-cache-timeout uint32;

         This option specifies the timeout in seconds for ARP cache entries.

       option associated-ip ip-address [, ip-address... ];

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

         This option is not user configurable.

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

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

       option bcms-controller-names domain-list;

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

       option bootfile-name text;

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

       option boot-size uint16;

         This  option  specifies the length in 512-octet blocks of the default
         boot image for the client.

       option broadcast-address ip-address;

         This option specifies the broadcast address in use  on  the  client's
         subnet.   Legal  values for broadcast addresses are specified in sec-
         tion 3.2.1.3 of STD 3 (RFC1122).

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

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

         This option is included based on RFC 5417.

       option client-last-transaction-time uint32;

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

         This option is not user configurable.

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

         The cookie server option specifies a list of RFC 865  cookie  servers
         available  to the client.  Servers should be listed in order of pref-
         erence.

       option default-ip-ttl uint8;

         This option specifies the default time-to-live that the client should
         use on outgoing datagrams.

       option default-tcp-ttl uint8;

         This option specifies the default TTL that the client should use when
         sending TCP segments.  The minimum value is 1.

       option default-url string;

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

       option dhcp-client-identifier string;

         This option can be used to specify a DHCP client identifier in a host
         declaration, so that dhcpd can  find  the  host  record  by  matching
         against the client identifier.

         Please  be  aware that some DHCP clients, when configured with client
         identifiers that are ASCII text, will prepend a  zero  to  the  ASCII
         text.  So you may need to write:

              option dhcp-client-identifier "\0foo";

         rather than:

              option dhcp-client-identifier "foo";

       option dhcp-lease-time uint32;

         This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
         to allow the client to request a lease time for the IP address.  In a
         server  reply  (DHCPOFFER), a DHCP server uses this option to specify
         the lease time it is willing to offer.

         This option is not directly user configurable in the server; refer to
         the   max-lease-time   and   default-lease-time   server  options  in
         dhcpd.conf(5).

       option dhcp-max-message-size uint16;

         This option, when sent by the client, specifies the maximum  size  of
         any  response that the server sends to the client.  When specified on
         the server, if the client did not send  a  dhcp-max-message-size  op-
         tion, the size specified on the server is used.  This works for BOOTP
         as well as DHCP responses.

       option dhcp-message text;

         This option is used by a DHCP server to provide an error message to a
         DHCP  client in a DHCPNAK message in the event of a failure. A client
         may use this option in a DHCPDECLINE  message  to  indicate  why  the
         client declined the offered parameters.

         This option is not user configurable.

       option dhcp-message-type uint8;

         This  option,  sent  by both client and server, specifies the type of
         DHCP message contained in the DHCP packet. Possible values (taken di-
         rectly from RFC2132) are:

                      1     DHCPDISCOVER
                      2     DHCPOFFER
                      3     DHCPREQUEST
                      4     DHCPDECLINE
                      5     DHCPACK
                      6     DHCPNAK
                      7     DHCPRELEASE
                      8     DHCPINFORM

         This option is not user configurable.

       option dhcp-option-overload uint8;

         This  option  is  used  to  indicate  that the DHCP 'sname' or 'file'
         fields are being overloaded by using them to carry  DHCP  options.  A
         DHCP  server  inserts this option if the returned parameters will ex-
         ceed the usual space allotted for options.

         If this option is present, the client interprets the specified  addi-
         tional  fields  after it concludes interpretation of the standard op-
         tion fields.

         Legal values for this option are:

                      1     the 'file' field is used to hold options
                      2     the 'sname' field is used to hold options
                      3     both fields are used to hold options

         This option is not user configurable.

       option dhcp-parameter-request-list uint8 [, uint8... ];

         This option, when sent by the client,  specifies  which  options  the
         client  wishes  the  server  to  return.   Normally,  in the ISC DHCP
         client, this is done using the request statement.  If this option  is
         not specified by the client, the DHCP server will normally return ev-
         ery option that is valid in scope and that fits into the reply.  When
         this option is specified on the server, the server returns the speci-
         fied 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 re-
         sponse of the DHCP server for clients that may need  a  more  limited
         set of options than those the server would normally return.

       option dhcp-rebinding-time uint32;

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

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

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

       option dhcp-renewal-time uint32;

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

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

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

       option dhcp-requested-address ip-address;

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

         This option is not user configurable.

       option dhcp-server-identifier ip-address;

         This option is used in DHCPOFFER and DHCPREQUEST  messages,  and  may
         optionally  be  included  in  the DHCPACK and DHCPNAK messages.  DHCP
         servers include this option in the DHCPOFFER in order  to  allow  the
         client  to  distinguish  between  lease offers.  DHCP clients use the
         contents of the 'server identifier' field as the destination  address
         for  any DHCP messages unicast to the DHCP server.  DHCP clients also
         indicate which of several lease offers is being accepted by including
         this option in a DHCPREQUEST message.

         The value of this option is the IP address of the server.

         This option is not directly user configurable. See the server-identi-
         fier server option in dhcpd.conf(5).

       option domain-name text;

         This option specifies the domain name that client should use when re-
         solving hostnames via the Domain Name System.

       option domain-name-servers ip-address [, ip-address...  ];

         The domain-name-servers option specifies a list of Domain Name System
         (STD 13, RFC 1035) name servers available  to  the  client.   Servers
         should be listed in order of preference.

       option domain-search domain-list;

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

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

       option extensions-path text;

         This  option  specifies  the name of a file containing additional op-
         tions to be interpreted according to the DHCP option format as speci-
         fied in RFC2132.

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

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

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

         This option specifies a list of X Window System Font  servers  avail-
         able to the client. Servers should be listed in order of preference.

       option geoconf-civic string;

         A string to hold the geoconf civic structure.

         This option is included based on RFC 4776.

       option host-name string;

         This  option  specifies  the name of the client.  The name may or may
         not be qualified with the local domain name (it is preferable to  use
         the domain-name option to specify the domain name).  See RFC 1035 for
         character set restrictions.  This option is only honored by dhclient-
         script(8) if the hostname for the client machine is not set.

       option ieee802-3-encapsulation flag;

         This  option  specifies whether or not the client should use Ethernet
         Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the in-
         terface  is  an Ethernet.  A value of false indicates that the client
         should use RFC 894 encapsulation.  A value of  true  means  that  the
         client should use RFC 1042 encapsulation.

       option ien116-name-servers ip-address [, ip-address...  ];

         The  ien116-name-servers  option  specifies  a  list  of IEN 116 name
         servers available to the client.  Servers should be listed  in  order
         of preference.

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

         The  impress-server option specifies a list of Imagen Impress servers
         available to the client.  Servers should be listed in order of  pref-
         erence.

       option interface-mtu uint16;

         This  option specifies the MTU to use on this interface.  The minimum
         legal value for the MTU is 68.

       option ip-forwarding flag;

         This option specifies whether the  client  should  configure  its  IP
         layer  for packet forwarding.  A value of false means disable IP for-
         warding, and a value of true means enable IP forwarding.

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

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

       option loader-configfile text

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

         This option is included based on RFC 5071.

       option loader-pathprefix text

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

         This option is included based on RFC 5071.

       option loader-reboottime uint32

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

         This option is included based on RFC 5071.

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

         The  log-server  option  specifies  a list of MIT-LCS UDP log servers
         available to the client.  Servers should be listed in order of  pref-
         erence.

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

         The  LPR  server  option  specifies  a  list of RFC 1179 line printer
         servers available to the client.  Servers should be listed  in  order
         of preference.

       option mask-supplier flag;

         This  option  specifies  whether  or not the client should respond to
         subnet mask requests using ICMP.  A value of false indicates that the
         client  should  not  respond.   A value of true means that the client
         should respond.

       option max-dgram-reassembly uint16;

         This option specifies the  maximum  size  datagram  that  the  client
         should be prepared to reassemble.  The minimum legal value is 576.

       option merit-dump text;

         This  option  specifies the path-name of a file to which the client's
         core image should be dumped in the event  the  client  crashes.   The
         path is formatted as a character string consisting of characters from
         the NVT ASCII character set.

       option mobile-ip-home-agent ip-address [, ip-address... ];

         This option specifies a list of IP  addresses  indicating  mobile  IP
         home  agents available to the client.  Agents should be listed in or-
         der of preference, although normally there  will  be  only  one  such
         agent.

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

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

         This option is included based on RFC 2937.

       option nds-context string;

         The nds-context option specifies the name of the initial Netware  Di-
         rectory Service for an NDS client.

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

         The  nds-servers  option  specifies  a  list  of  IP addresses of NDS
         servers.

       option nds-tree-name string;

         The nds-tree-name option specifies NDS tree name that the NDS  client
         should use.

       option netbios-dd-server ip-address [, ip-address...  ];

         The  NetBIOS  datagram  distribution server (NBDD) option specifies a
         list of RFC 1001/1002 NBDD servers listed in order of preference.

       option netbios-name-servers ip-address [, ip-address...];

         The NetBIOS name  server  (NBNS)  option  specifies  a  list  of  RFC
         1001/1002  NBNS  name servers listed in order of preference.  NetBIOS
         Name Service is currently more commonly referred to  as  WINS.   WINS
         servers can be specified using the netbios-name-servers option.

       option netbios-node-type uint8;

         The NetBIOS node type option allows NetBIOS over TCP/IP clients which
         are configurable to be configured as described in RFC 1001/1002.  The
         value  is  specified  as  a  single octet which identifies the client
         type.

         Possible node types are:

         1    B-node: Broadcast - no WINS

         2    P-node: Peer - WINS only

         4    M-node: Mixed - broadcast, then WINS

         8    H-node: Hybrid - WINS, then broadcast

       option netbios-scope string;

         The NetBIOS scope option specifies the NetBIOS over TCP/IP scope  pa-
         rameter  for  the  client as specified in RFC 1001/1002. See RFC1001,
         RFC1002, and RFC1035 for character-set restrictions.

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

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

       option netinfo-server-tag text;

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

       option nis-domain text;

         This option specifies the name of the client's NIS (Sun  Network  In-
         formation  Services)  domain.  The domain is formatted as a character
         string consisting of characters from the NVT ASCII character set.

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

         This option specifies a list of IP addresses indicating  NIS  servers
         available  to the client.  Servers should be listed in order of pref-
         erence.

       option nisplus-domain text;

         This option specifies the name of the client's NIS+ domain.  The  do-
         main is formatted as a character string consisting of characters from
         the NVT ASCII character set.

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

         This option specifies a list of IP addresses indicating NIS+  servers
         available  to the client.  Servers should be listed in order of pref-
         erence.

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

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

       option non-local-source-routing flag;

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

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

         This  option  specifies  a  list  of IP addresses indicating NTP (RFC
         5905) servers available to the client.  Servers should be  listed  in
         order of preference.

       option nwip-domain string;

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

       option nwip-suboptions string;

         A sequence of suboptions for NetWare/IP clients - see RFC2242 for de-
         tails.  Normally this option is set by specifying specific NetWare/IP
         suboptions - see the NETWARE/IP SUBOPTIONS section for more  informa-
         tion.

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

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

         This option is included based on RFC 4578.

       option pxe-interface-id uint8 uint8 uint8

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

         This option is included based on RFC 4578.

       option pxe-client-id uint8 string

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

         This option is included based on RFC 4578.

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

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

         This option is included based on RFC 5969.

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

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

         This option is included based on RFC 5192.

       option path-mtu-aging-timeout uint32;

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

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

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

       option pcode text;

         This option specifies a string suitable for the TZ variable.

         This option is included based on RFC 4833.

       option perform-mask-discovery flag;

         This option specifies whether or not the client should perform subnet
         mask discovery using ICMP.  A  value  of  false  indicates  that  the
         client should not perform mask discovery.  A value of true means that
         the client should perform mask discovery.

       option policy-filter ip-address ip-address
                         [, ip-address ip-address...];

         This option specifies policy filters for  non-local  source  routing.
         The filters consist of a list of IP addresses and masks which specify
         destination/mask pairs with which to filter incoming source routes.

         Any source routed datagram whose next-hop address does not match  one
         of the filters should be discarded by the client.

         See STD 3 (RFC1122) for further information.

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

         The  POP3 server option specifies a list of POP3 servers available to
         the client.  Servers should be listed in order of preference.

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

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

         This option is included based on RFC 6731.

       option resource-location-servers ip-address
                                     [, ip-address...];

         This option specifies a list of RFC  887  Resource  Location  servers
         available  to the client.  Servers should be listed in order of pref-
         erence.

       option root-path text;

         This option specifies the path-name that contains the  client's  root
         disk.   The  path  is  formatted  as a character string consisting of
         characters from the NVT ASCII character set.

       option router-discovery flag;

         This option specifies  whether  or  not  the  client  should  solicit
         routers  using the Router Discovery mechanism defined in RFC 1256.  A
         value of false indicates that the client should  not  perform  router
         discovery.   A  value  of  true  means that the client should perform
         router discovery.

       option router-solicitation-address ip-address;

         This option specifies the address to which the client should transmit
         router solicitation requests.

       option routers ip-address [, ip-address...  ];

         The  routers  option  specifies a list of IP addresses for routers on
         the client's subnet.  Routers should be listed in  order  of  prefer-
         ence.

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

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

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

         Also,  please  be  aware that some companies may refer to SLP as NDS.
         If you have an NDS directory agent whose address you need to  config-
         ure, the slp-directory-agent option should work.

       option slp-service-scope boolean text;

         The  Service  Location  Protocol  Service  Scope Option specifies two
         things: a list of service scopes for SLP, and whether the use of this
         list  is  mandatory.   If  the initial boolean value is true, the SLP
         agent should only use the list of scopes  provided  in  this  option;
         otherwise,  it  may use its own static configuration in preference to
         the list provided in this option.

         The text string should be a comma-separated list of scopes  that  the
         SLP agent should use.  It may be omitted, in which case the SLP Agent
         will use the aggregated list of scopes of all directory agents  known
         to the SLP agent.

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

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

       option static-routes ip-address ip-address
                         [, ip-address ip-address...];

         This option specifies a list of static routes that the client  should
         install  in its routing cache.  If multiple routes to the same desti-
         nation are specified, they are listed in descending order  of  prior-
         ity.

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

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

       option streettalk-directory-assistance-server ip-address
                                                  [, ip-address...];

         The  StreetTalk Directory Assistance (STDA) server option specifies a
         list of STDA servers available to  the  client.   Servers  should  be
         listed in order of preference.

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

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

       option subnet-mask ip-address;

         The  subnet mask option specifies the client's subnet mask as per RFC
         950.  If no subnet mask option is provided anywhere in  scope,  as  a
         last  resort  dhcpd will use the subnet mask from the subnet declara-
         tion for the network on which an address is being assigned.  However,
         any  subnet-mask  option declaration that is in scope for the address
         being assigned will override the subnet mask specified in the  subnet
         declaration.

       option subnet-selection ip-address;

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

       This option is not user configurable in the server.

       option swap-server ip-address;

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

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

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

         This option is included based on RFC 5859

       option tcp-keepalive-garbage flag;

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

       option tcp-keepalive-interval uint32;

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

       option tcode text;

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

         This option is included based on RFC 4833.

       option tftp-server-name text;

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

       option time-offset int32;

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

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

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

       option trailer-encapsulation flag;

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

       option uap-servers text;

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

       option user-class string;

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

       option v4-access-domain domain-name;

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

         This option is included based on RFC 5986.

       option v4-lost domain-name;

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

         This option is included based on RFC 5223.

       option vendor-class-identifier string;

         This option is used by some DHCP clients to identify the vendor  type
         and  possibly the configuration of a DHCP client.  The information is
         a string of bytes whose contents are specific to the vendor  and  are
         not  specified  in  a  standard.  To see what vendor class identifier
         clients are sending, you can write the following in your DHCP  server
         configuration file:

         set vendor-string = option vendor-class-identifier;

         This  will  result  in  all entries in the DHCP server lease database
         file for clients that sent vendor-class-identifier options  having  a
         set statement that looks something like this:

         set vendor-string = "SUNW.Ultra-5_10";

         The  vendor-class-identifier  option  is  normally  used  by the DHCP
         server to determine the options that are returned in  the  vendor-en-
         capsulated-options  option.   Please  see the VENDOR ENCAPSULATED OP-
         TIONS section later in this manual page for further information.

       option vendor-encapsulated-options string;

         The vendor-encapsulated-options option can contain  either  a  single
         vendor-specific  value  or  one  or  more vendor-specific suboptions.
         This option is not normally specified in the DHCP  server  configura-
         tion  file - instead, a vendor class is defined for each vendor, ven-
         dor class suboptions are defined, values for those suboptions are de-
         fined, and the DHCP server makes up a response on that basis.

         Some  default  behaviours  for  well-known  DHCP client vendors (cur-
         rently, the Microsoft Windows 2000 DHCP client) are configured  auto-
         matically,  but  otherwise this must be configured manually - see the
         VENDOR ENCAPSULATED OPTIONS section later in this manual page for de-
         tails.

       option vivso string;

         The  vivso option can contain multiple separate options, one for each
         32-bit Enterprise ID.  Each Enterprise-ID discriminated  option  then
         contains additional options whose format is defined by the vendor who
         holds that ID.  This option is usually not configured  manually,  but
         rather is configured via intervening option definitions.  Please also
         see the VENDOR ENCAPSULATED OPTIONS section later in this manual page
         for details.

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

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

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

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

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

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

       option agent.circuit-id string;

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

       option agent.remote-id string;

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

       option agent.DOCSIS-device-class uint32;

         The DOCSIS-device-class suboption is intended to  convey  information
         about the host endpoint, hardware, and software, that either the host
         operating system or the DHCP server may not  otherwise  be  aware  of
         (but  the  relay  is  able to distinguish).  This is implemented as a
         32-bit field (4 octets), each bit representing a flag describing  the
         host  in  one  of these ways.  So far, only bit zero (being the least
         significant bit) is defined in RFC3256.  If this bit is set  to  one,
         the  host  is  considered  a  CPE Controlled Cable Modem (CCCM).  All
         other bits are reserved.

       option agent.link-selection ip-address;

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

THE CLIENT FQDN SUBOPTIONS
       The Client FQDN option, currently defined in the Internet Draft  draft-
       ietf-dhc-fqdn-option-00.txt  is  not  a  standard yet, but is in suffi-
       ciently wide use already that we have implemented it.  Due to the  com-
       plexity  of  the  option  format, we have implemented it as a suboption
       space rather than a single option.  In general this option  should  not
       be configured by the user - instead it should be used as part of an au-
       tomatic DNS update system.

       option fqdn.no-client-update flag;

         When the client sends this, if it is true, it means the  client  will
         not  attempt  to update its A record.  When sent by the server to the
         client, it means that the client should not update its own A record.

       option fqdn.server-update flag;

         When the client sends this to the server, it is requesting  that  the
         server  update  its A record.  When sent by the server, it means that
         the server has updated (or is about to update) the client's A record.

       option fqdn.encoded flag;

         If true, this indicates that the domain name included in  the  option
         is  encoded in DNS wire format, rather than as plain ASCII text.  The
         client normally sets this to false if it  doesn't  support  DNS  wire
         format  in  the  FQDN option.  The server should always send back the
         same value that the client sent.  When this value is set on the  con-
         figuration side, it controls the format in which the fqdn.fqdn subop-
         tion is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

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

       option fqdn.fqdn text;

         Specifies the domain name that the client wishes to use.  This can be
         a fully-qualified domain name, or a single label.   If  there  is  no
         trailing  '.'  character  in the name, it is not fully-qualified, and
         the server will generally update that name  in  some  locally-defined
         domain.

       option fqdn.hostname --never set--;

         This  option  should  never be set, but it can be read back using the
         option and config-option operators in an expression, in which case it
         returns  the first label in the fqdn.fqdn suboption - for example, if
         the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will
         be "foo".

       option fqdn.domainname --never set--;

         This  option  should  never be set, but it can be read back using the
         option and config-option operators in an expression, in which case it
         returns all labels after the first label in the fqdn.fqdn suboption -
         for example, if the value of fqdn.fqdn  is  "foo.example.com.",  then
         fqdn.domainname  will  be "example.com.".  If this suboption value is
         not set, it means that an unqualified name was sent in the  fqdn  op-
         tion, or that no fqdn option was sent at all.

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

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

       option nwip.nsq-broadcast flag;

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

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

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

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

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

       option nwip.autoretries uint8;

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

       option nwip.autoretry-secs uint8;

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

       option nwip.nwip-1-1 uint8;

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

       option nwip.primary-dss ip-address;

         Specifies the IP address of the Primary Domain SAP/RIP Service server
         (DSS)  for  this  NetWare/IP  domain.   The NetWare/IP administration
         utility uses this value as Primary DSS server when configuring a sec-
         ondary DSS server.

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

       option dhcp6.client-id string;

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

         duid-llt

         duid-en

         duid-ll

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

       option dhcp6.server-id string;

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

       option dhcp6.ia-na string;

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

       option dhcp6.ia-ta string;

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

       option dhcp6.ia-addr string;

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

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

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

       option dhcp6.preference uint8;

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

       option dhcp6.elapsed-time uint16;

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

       option dhcp6.relay-msg string;

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

       option dhcp6.unicast ip6-address;

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

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

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

       option dhcp6.rapid-commit ;

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

       option dhcp6.vendor-opts string;

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

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

       option dhcp6.interface-id string;

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

       option dhcp6.reconf-msg dhcpv6-message;

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

       option dhcp6.reconf-accept ;

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

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

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

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

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

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

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

       option dhcp6.domain-search domain-list;

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

       option dhcp6.ia-pd string;

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

       option dhcp6.ia-prefix string;

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

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

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

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

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

       option nis-domain-name domain-list;

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

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

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

       option nisp-domain-name domain-list;

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

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

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

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

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

       option dhcp6.info-refresh-time uint32;

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

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

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

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

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

       option dhcp6.geoconf-civic string;

         A string to hold the geoconf civic structure.

         This option is included based on RFC 4776.

       option dhcp6.remote-id string;

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

       option dhcp6.subscriber-id string;

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

       option dhcp6.fqdn string;

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

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

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

         This option is included based on RFC 5192.

       option dhcp6.new-posix-timezone text;

         This option specifies a string suitable for the TZ variable.

         This option is included based on RFC 4833.

       option dhcp6.new-tzdb-timezone text;

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

         This option is included based on RFC 4833.

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

         A list of the options requested by the relay agent.

         This option is included based on RFC 4994.

       option dhcp6.lq-query string;

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

       option dhcp6.client-data string;

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

       option dhcp6.clt-time uint32;

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

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

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

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

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

       option dhcp6.v6-lost domain-name;

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

         This option is included based on RFC 5223.

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

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

         This option is included based on RFC 5417.

       option dhcp6.relay-id string;

         The DUID for the relay agent.

         This option is included based on RFC 5460.

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

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

         This option is included based on RFC5986.

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

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

         This option is included based on RFC 6011.

       option dhcp6.bootfile-url text;

         The URL for a boot file.

         This option is included based on RFC 5970.

       option dhcp6.bootfile-param string;

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

         This option is included based on RFC 5970.

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

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

         This option is included based on RFC 5970.

       option dhcp6.nii uint8 uint8 uint8;

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

         This option is included based on RFC5970.

       option dhcp6.aftr-name domain-name;

         A domain name of the AFTR tunnel endpoint.

         This option is included based on RFC 6334.

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

         A domain name for the ERP domain.

         This option is included based on RFC 6440.

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

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

         This option is included based on RFC 6731.

       option dhcp6.client-linklayer-addr string;

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

         This option is included based on RFC 6939.

       option dhcp6.link-address ip6-address;

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

         This option is included based on RFC 6977.

       option dhcp6.solmax-rt uint32;

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

         This option is included based on RFC 7083.

       option dhcp6.inf-max-rt uint32;

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

         This option is included based on RFC 7083.

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

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

DEFINING NEW OPTIONS
       The Internet Systems Consortium DHCP client and server provide the  ca-
       pability  to  define new options.  Each DHCP option has a name, a code,
       and a structure.  The name is used by you to refer to the option.   The
       code is a number, used by the DHCP server and client to refer to an op-
       tion.  The structure describes what the contents  of  an  option  looks
       like.

       To define a new option, you need to choose a name for it that is not in
       use for some other option - for example, you can't use "host-name"  be-
       cause  the  DHCP  protocol already defines a host-name option, which is
       documented earlier in this manual page.  If an option name doesn't  ap-
       pear in this manual page, you can use it, but it's probably a good idea
       to put some kind of unique string at the beginning so you can  be  sure
       that  future  options don't take your name.  For example, you might de-
       fine an option, "local-host-name", feeling some confidence that no  of-
       ficial DHCP option name will ever start with "local".

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

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

       New options are declared as follows:

       option new-name code new-code = definition ;

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

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

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

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

       INTEGER

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

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

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

       IP-ADDRESS

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

       An option whose structure is an IP address can be expressed either as a
       domain name or as a dotted quad.  So the following is an example use of
       the ip-address type:

       option sql-server-address code 193 = ip-address;
       option sql-server-address sql.example.com;

       IP6-ADDRESS

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

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

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

       TEXT

       option new-name code new-code = text ;

       An option whose type is text will encode an ASCII text string.  For ex-
       ample:

       option sql-default-connection-name code 194 = text;
       option sql-default-connection-name "PRODZA";

       DATA STRING

       option new-name code new-code = string ;

       An  option whose type is a data string is essentially just a collection
       of bytes, and can be specified either as quoted  text,  like  the  text
       type,  or  as  a list of hexadecimal contents separated by colons whose
       values must be between 0 and FF.  For example:

       option sql-identification-token code 195 = string;
       option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;

       DOMAIN-LIST

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

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

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

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

       ENCAPSULATION

       option new-name code new-code = encapsulate identifier ;

       An  option  whose  type is encapsulate will encapsulate the contents of
       the option space specified in identifier.  Examples of encapsulated op-
       tions  in  the DHCP protocol as it currently exists include the vendor-
       encapsulated-options option, the netware-suboptions option and the  re-
       lay-agent-information option.

       option space local;
       option local.demo code 1 = text;
       option local-encapsulation code 197 = encapsulate local;
       option local.demo "demo";

       ARRAYS

       Options  can  contain  arrays  of any of the above types except for the
       text and data string types, which aren't currently supported in arrays.
       An example of an array definition is as follows:

       option kerberos-servers code 200 = array of ip-address;
       option kerberos-servers 10.20.10.1, 10.20.11.1;

       RECORDS

       Options  can  also  contain data structures consisting of a sequence of
       data types, which is sometimes called a record type.  For example:

       option contrived-001 code 201 = { boolean, integer 32, text };
       option contrived-001 on 1772 "contrivance";

       It's also possible to have options that are arrays of records, for  ex-
       ample:

       option new-static-routes code 201 = array of {
            ip-address, ip-address, ip-address, integer 8 };
       option static-routes
            10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
            10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
            10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;

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

       The  value  of  these options can be set in one of two ways.  The first
       way is to simply specify the data directly, using a text  string  or  a
       colon-separated  list of hexadecimal values.  For help in forming these
       strings, please refer to RFC2132 for the DHCPv4 Vendor Specific  Infor-
       mation  Option, RFC3925 for the DHCPv4 Vendor Identified Vendor Sub Op-
       tions, or RFC3315 for the DHCPv6  Vendor-specific  Information  Option.
       For example:

       option vendor-encapsulated-options
           2:4:
            AC:11:41:1:
           3:12:
            73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
           4:12:
            2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
       option vivso
           00:00:09:bf:0E:
            01:0c:
                48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
       option dhcp6.vendor-opts
           00:00:09:bf:
            00:01:00:0c:
                48:65:6c:6c:6f:20:77:6f:72:6c:64:21;

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

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

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

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

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

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

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

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

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

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

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

       Once you have defined an option space and the format of  some  options,
       you can set up scopes that define values for those options, and you can
       say when to use them.  For example, suppose you want to handle two dif-
       ferent  classes of clients.  Using the option space definition shown in
       the previous example, you can send different option values to different
       clients  based  on  the vendor-class-identifier option that the clients
       send, as follows:

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

       subclass "vendor-classes" "SUNW.Ultra-5_10" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/sparc";
       }

       subclass "vendor-classes" "SUNW.i86pc" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/i86pc";
       }

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

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

       option docsis.tftp-servers ::1;

       As you can see in the preceding example, regular scoping  rules  apply,
       so  you can define values that are global in the global scope, and only
       define values that are specific to a  particular  class  in  the  local
       scope.   The  vendor-option-space  declaration tells the DHCP server to
       use options in the SUNW option space to construct the DHCPv4 vendor-en-
       capsulated-options  option.   This is a limitation of that option - the
       DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi-
       nitions all at once (even transmitted to the same client), so it is not
       necessary to configure this.

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

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

                                                               dhcp-options(5)
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