dhcp-options(5)                                                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
       address  (e.g.,  239.254.197.10)  or  as  a  domain  name  (e.g.,  haa-
       gen.isc.org).  When entering a domain name, be sure  that  that  domain
       name resolves to a single IP address.

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

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

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

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

       The domain-name data type specifies a domain name, which  must  not  be
       enclosed  in  double  quotes.   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
       option you would edit the includes/site.h file and comment out the def-
       inition 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
       below may not yet be implemented,  but  it  is  possible  to  use  such
       options  by  defining  them  in the configuration file.  Please see the
       DEFINING NEW OPTIONS heading later in this document for  more  informa-
       tion.

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

       The standard options are:

       option all-subnets-local flag;

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

       option arp-cache-timeout uint32;

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

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

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

       option bcms-controller-names domain-list;

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

       option bootfile-name text;

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

       option boot-size uint16;

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

       option broadcast-address ip-address;

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

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

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

         This option is included based on RFC 5417.

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

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

       option default-ip-ttl uint8;

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

       option default-tcp-ttl uint8;

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

       option default-url string;

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

       option dhcp-client-identifier string;

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

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

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

         rather than:

              option dhcp-client-identifier "foo";

       option dhcp-lease-time uint32;

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

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

       option dhcp-max-message-size uint16;

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

       option dhcp-message text;

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

         This option is not user configurable.

       option dhcp-message-type uint8;

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

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

         This option is not user configurable.

       option dhcp-option-overload uint8;

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

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

         Legal values for this option are:

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

         This option is not user configurable.


       option dhcp-parameter-request-list uint16 [, uint16... ];

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

       option dhcp-rebinding-time uint32;

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

         This option is 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
         resolving hostnames via the Domain Name System.

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

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

       option domain-search domain-list;

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

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

       option extensions-path text;

         This  option  specifies  the  name  of  a  file containing additional
         options to be interpreted according to  the  DHCP  option  format  as
         specified in RFC2132.

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

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

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

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

       option 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
         interface is an Ethernet.  A value of false indicates that the client
         should  use  RFC  894  encapsulation.  A value of true means that the
         client should use RFC 1042 encapsulation.

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

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

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

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

       option interface-mtu uint16;

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

       option ip-forwarding flag;

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

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

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

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

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

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

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

       option mask-supplier flag;

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

       option max-dgram-reassembly uint16;

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

       option merit-dump text;

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

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

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

       option 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
         Directory Service for an NDS client.

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

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

       option nds-tree-name string;

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

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

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

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

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

       option netbios-node-type uint8;

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

         Possible node types are:


         1    B-node: Broadcast - no WINS

         2    P-node: Peer - WINS only

         4    M-node: Mixed - broadcast, then WINS

         8    H-node: Hybrid - WINS, then broadcast

       option netbios-scope string;

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

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

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

       option netinfo-server-tag text;

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

       option nis-domain text;

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

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

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

       option nisplus-domain text;

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

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

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

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

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

       option non-local-source-routing flag;

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

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

         This option specifies a list of  IP  addresses  indicating  NTP  (RFC
         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
         details.  Normally this option is set  by  specifying  specific  Net-
         Ware/IP  suboptions  - see the NETWARE/IP SUBOPTIONS section for more
         information.

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

         This  option  contains infomration 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
         addresses.

         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
         addresses 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
         domains for whcih the RDNSS has sepcial 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 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 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
         requests encapsulated in the User Authentication Protocol (UAP).  UAP
         servers can accept either HTTP 1.1 or SSLv3 connections.  If the list
         includes  a  URL  that  does not contain a port component, the normal
         default port is assumed (i.e., port 80 for  http  and  port  443  for
         https).  If the list includes a URL that does not contain a path com-
         ponent, the path /uap is assumed.  If more than one URL is  specified
         in this list, the URLs are separated by spaces.

       option user-class string;

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

       option 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-
         encapsulated-options option.   Please  see  the  VENDOR  ENCAPSULATED
         OPTIONS section later in this manual page for further information.

       option vendor-encapsulated-options string;

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

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

       option vivso string;

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

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

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

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

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

RELAY AGENT INFORMATION OPTION
       An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
       encapsulated options that a relay agent can add to a DHCP  packet  when
       relaying it to the DHCP server.  The server can then make address 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
       define values for these options in the server, although it is permissi-
       ble.  These options are not supported in the client.

       option agent.circuit-id string;

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

       option fqdn.no-client-update flag;

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

       option fqdn.server-update flag;

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

       option fqdn.encoded flag;

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

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

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

       option fqdn.fqdn text;

         Specifies the domain name that the client wishes to use.  This can be
         a  fully-qualified  domain  name,  or a single label.  If there is no
         trailing ´.´ 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.hostname will be "example.com.".  If this suboption value is not
         set,  it  means that an unqualified name was sent in the fqdn option,
         or that no fqdn option was sent at all.

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

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

       option nwip.nsq-broadcast flag;

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

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

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

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

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

       option nwip.autoretries uint8;

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

       option nwip.autoretry-secs uint8;

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

       option nwip.nwip-1-1 uint8;

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

       option nwip.primary-dss ip-address;

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

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

       option dhcp6.client-id string;

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

         duid-llt

         duid-en

         duid-ll

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

       option dhcp6.server-id string;

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

       option dhcp6.ia-na string;

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

       option dhcp6.ia-ta string;

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

       option dhcp6.ia-addr string;

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

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

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

       option dhcp6.preference uint8;

         The preference option informs a DHCPv6 client which server  is  ´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 Renew packets from their clients by exchanging
         UDP  unicasts  with  them.   Normally,  DHCPv6 clients will multicast
         their Renew messages.  This may be  configured  on  the  server,  and
         should be configured as an address the server is ready to reply to.

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

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

       option dhcp6.rapid-commit ;

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

       option dhcp6.vendor-opts string;

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

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

       option dhcp6.interface-id string;

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

       option dhcp6.reconf-msg dhcpv6-message;

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

       option dhcp6.reconf-accept ;

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

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

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

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

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

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

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

       option dhcp6.domain-search domain-list;

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

       option dhcp6.ia-pd string;

         The  ia-pd  option is manufactured by clients and servers to create a
         Prefix Delegation binding - to delegate an IPv6 prefix to the client.
         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
         option.

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

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

       option dhcp6.info-refresh-time uint32;

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

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

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

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

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

       option dhcp6.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;

         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
         addresses 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
         addresses 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
       option, 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
       capability to define new options.  Each DHCP option has a name, a code,
       and a structure.  The name is used by you to refer to the option.   The
       code  is  a  number,  used by the DHCP server and client to refer to an
       option.  The structure describes what the contents of an  option  looks
       like.

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

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

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

       New options are declared as follows:

       option new-name code new-code = definition ;

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

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

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

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

       INTEGER

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

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

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

       IP-ADDRESS

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

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

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

       IP6-ADDRESS

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

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

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


       TEXT

       option new-name code new-code = text ;

       An option whose type is text will encode an  ASCII  text  string.   For
       example:

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


       DATA STRING

       option new-name code new-code = string ;

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

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


       DOMAIN-LIST

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

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

       When in doubt, omit the compressed keyword.  When the software 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
       options in the DHCP protocol as it currently exists include the vendor-
       encapsulated-options option,  the  netware-suboptions  option  and  the
       relay-agent-information option.

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


       ARRAYS

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

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

       RECORDS

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

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

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

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


VENDOR ENCAPSULATED OPTIONS
       The DHCP protocol defines the vendor-encapsulated-options option, which
       allows vendors to define their own options that will be  sent  encapsu-
       lated in a standard DHCP option.  It also defines the Vendor Identified
       Vendor Sub Options option ("VIVSO"), and the  DHCPv6  protocol  defines
       the  Vendor-specific Information Option ("VSIO").  The format of all of
       these options is usually internally a string of options,  similarly  to
       other  normal  DHCP options.  The VIVSO and VSIO options differ in that
       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
       Options, or RFC3315 for the DHCPv6 Vendor-specific Information  Option.
       For example:

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

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

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

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

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

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

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

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

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

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

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

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

       Once you have defined an option space and the format of  some  options,
       you can set up scopes that define values for those options, and you can
       say when to use them.  For example, suppose you want to handle two 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-
       encapsulated-options option.  This is a limitation of that option - the
       DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi-
       nitions all at once (even transmitted to the same client), so it is not
       necessary to configure this.

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

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



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