Provided by: isc-dhcp-common_4.3.3-5ubuntu12_amd64 bug

NAME

       dhcp-options - Dynamic Host Configuration Protocol options

DESCRIPTION

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

REFERENCE: OPTION STATEMENTS

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

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

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

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

       The int32 data type specifies a signed 32-bit integer.  The uint32 data type specifies  an
       unsigned  32-bit  integer.   The  int16  and uint16 data types specify signed and unsigned
       16-bit integers.  The int8  and  uint8  data  types  specify  signed  and  unsigned  8-bit
       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.example.com").

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

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

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

SETTING OPTION VALUES USING EXPRESSIONS

       Sometimes it's helpful to be able to set the value of a DHCP option based  on  some  value
       that  the  client  has  sent.   To  do this, you can use expression evaluation.  The dhcp-
       eval(5) manual page describes how to write  expressions.   To  assign  the  result  of  an
       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 definitions will be
       included in the code based on the definition of an argument for the RFC that  defines  the
       option  in  includes/site.h.   This  provides  you  with  a method for over-riding the ISC
       definitions if necessary - 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 definition 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 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 conditional expressions. However, the value of the option cannot be used in the
       configuration  file  of  the sending agent, because the value is determined only after the
       configuration file has been processed. In the following documentation, such  options  will
       be shown as "not user configurable"

       The standard options are:

       option all-subnets-local flag;

         This  option  specifies  whether or not the client may assume that all subnets of the IP
         network to which the client is connected use the same MTU as the subnet of that  network
         to  which  the client is directly connected.  A value of true indicates that all subnets
         share the same MTU.  A value of false means that the  client  should  assume  that  some
         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 Multicast Controller
         Servers ("BCMS") controllers which the client may use.

       option bootfile-name text;

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

       option boot-size uint16;

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

       option broadcast-address ip-address;

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

       option 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 client-last-transaction-time uint32;

         This option is part of lease query.  It allows the receiver to determine 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 preference.

       option default-ip-ttl uint8;

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

       option default-tcp-ttl uint8;

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

       option default-url string;

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

       option dhcp-client-identifier string;

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

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

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

         rather than:

              option dhcp-client-identifier "foo";

       option dhcp-lease-time uint32;

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

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

       option dhcp-max-message-size uint16;

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

       option dhcp-message text;

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

         This option is not user configurable.

       option dhcp-message-type uint8;

         This option, sent by both  client  and  server,  specifies  the  type  of  DHCP  message
         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 additional fields after
         it concludes interpretation of the standard option fields.

         Legal values for this option are:

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

         This option is not user configurable.

       option dhcp-parameter-request-list 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  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  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 configured 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  configured  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-identifier  server  option
         in dhcpd.conf(5).

       option domain-name text;

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

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

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

       option domain-search domain-list;

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

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

       option extensions-path text;

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

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

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

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

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

       option 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 preference.

       option interface-mtu uint16;

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

       option ip-forwarding flag;

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

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

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

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

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

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

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

       option mask-supplier flag;

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

       option max-dgram-reassembly uint16;

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

       option merit-dump text;

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

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

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

       option 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 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 netinfo-server-tag text;

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

       option nis-domain text;

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

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

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

       option nisplus-domain text;

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

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

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

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

         The  NNTP  server  option  specifies  a  list  of  NNTP 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  details.   Normally
         this  option  is  set  by specifying specific NetWare/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 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 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 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 preference.

       option root-path text;

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

       option router-discovery flag;

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

       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 multicast
         discovery of SLP agents (see RFC2165 for details).

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

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

       option slp-service-scope boolean text;

         The Service Location Protocol Service Scope Option  specifies  two  things:  a  list  of
         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  destination  are  specified,  they  are
         listed in descending order of priority.

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

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

       option subnet-mask ip-address;

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

       option subnet-selection 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 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 declaration.   BOOTP  clients  are  unlikely  to
         support this option.  Some DHCP clients will support it, and others actually require it.

       option time-offset int32;

         The  time-offset  option  specifies  the  offset  of the client's subnet in seconds from
         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 preference.

       option trailer-encapsulation flag;

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

       option uap-servers text;

         This option specifies a list of URLs, each pointing to  a  user  authentication  service
         that  is  capable  of  processing  authentication  requests  encapsulated  in  the  User
         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 component, the path /uap is assumed.
         If more than one URL is specified in this list, the URLs are separated by spaces.

       option user-class string;

         This option is used by some DHCP clients as a  way  for  users  to  specify  identifying
         information  to  the  client.   This  can  be used in a similar way to the vendor-class-
         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 configuration file - instead, a vendor class is  defined  for  each  vendor,
         vendor  class  suboptions  are defined, values for those suboptions are defined, and the
         DHCP server makes up a response on that basis.

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

       option vivso string;

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

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

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

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

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

RELAY AGENT INFORMATION OPTION

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

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

       option agent.circuit-id string;

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

       option agent.remote-id string;

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

       option agent.DOCSIS-device-class uint32;

         The  DOCSIS-device-class  suboption  is  intended  to  convey information about the host
         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 useful in  those  cases  where  the  giaddr
         (where  responses  must  be  sent  to  the relay agent) is not on the same subnet as the
         client.  When this option is present in a packet from a relay  agent,  the  DHCP  server
         will use its contents to find a subnet declared in configuration, and from here take one
         step further backwards to any shared-network the  subnet  may  be  defined  within;  the
         client may be given any address within that shared network, as normally appropriate.

THE CLIENT FQDN SUBOPTIONS

       The  Client  FQDN  option,  currently  defined  in the Internet Draft draft-ietf-dhc-fqdn-
       option-00.txt is not a standard yet, but is in sufficiently wide use already that we  have
       implemented  it.   Due to the complexity of the option format, we have implemented it as a
       suboption space rather than a single  option.   In  general  this  option  should  not  be
       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 configuration
         side, it controls the format in which the fqdn.fqdn suboption is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

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

       option fqdn.fqdn text;

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

       option fqdn.hostname --never set--;

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

       option fqdn.domainname --never set--;

         This option should never be set, but it can be read back using the  option  and  config-
         option  operators  in an expression, in which case it returns all labels after the first
         label in  the  fqdn.fqdn  suboption  -  for  example,  if  the  value  of  fqdn.fqdn  is
         "foo.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 option, or that
         no fqdn option was sent at all.

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

THE NETWARE/IP SUBOPTIONS

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

       option nwip.nsq-broadcast flag;

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

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

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

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

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

       option nwip.autoretries uint8;

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

       option nwip.autoretry-secs uint8;

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

       option nwip.nwip-1-1 uint8;

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

       option nwip.primary-dss ip-address;

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

STANDARD DHCPV6 OPTIONS

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

       option dhcp6.client-id string;

         This  option  specifies  the  client's DUID identifier.  DUIDs are similar but different
         from DHCPv4 client identifiers - there are documented duid types:

         duid-llt

         duid-en

         duid-ll

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

       option dhcp6.server-id string;

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

       option dhcp6.ia-na string;

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

       option dhcp6.ia-ta string;

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

       option dhcp6.ia-addr string;

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

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

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

       option dhcp6.preference uint8;

         The  preference  option informs a DHCPv6 client which server is ´preferred´ for use on a
         given  subnet.   This  preference  is  only  applied  during  the  initial   stages   of
         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 multicast 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  applicable 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 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
         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 informationally only.

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

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

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

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

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

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

       option dhcp6.domain-search domain-list;

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

       option dhcp6.ia-pd string;

         The ia-pd option is manufactured by clients and servers to create  a  Prefix  Delegation
         binding  -  to  delegate  an  IPv6  prefix  to the client.  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 identify the prefix(es)
         allocated  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.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 available for the client
         to synchronize their clocks.

       option dhcp6.info-refresh-time uint32;

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

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

         The  bcms-server-d  option  contains  the  domain  names  of  local  BCMS (Broadcast and
         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 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 special 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 spaces, please contact your vendor and inform them about rfc3942.

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

       New options are declared as follows:

       option new-name code new-code = definition ;

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

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

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

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

       INTEGER

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

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

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

       IP-ADDRESS

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

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

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

       IP6-ADDRESS

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

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

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

       TEXT

       option new-name code new-code = text ;

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

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

       DATA STRING

       option new-name code new-code = string ;

       An  option  whose type is a data string is essentially just a collection of bytes, and can
       be specified either as quoted text, like the text  type,  or  as  a  list  of  hexadecimal
       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 compressed 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 encapsulated in a  standard  DHCP  option.   It
       also  defines  the  Vendor  Identified Vendor Sub Options option ("VIVSO"), and the DHCPv6
       protocol defines the Vendor-specific Information Option ("VSIO").  The format  of  all  of
       these  options  is  usually internally a string of options, similarly to other normal DHCP
       options.  The VIVSO and VSIO options differ in that they contain options  that  correspond
       to  vendor  Enterprise-ID numbers (assigned by IANA), which then contain options according
       to each Vendor's specifications.  You will need to refer to your vendor's documentation in
       order to form options to their specification.

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

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

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

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

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

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

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

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

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

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

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

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

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

       Once you have defined an option space and the format of  some  options,  you  can  set  up
       scopes  that  define  values  for  those  options,  and you can say when to use them.  For
       example, suppose you want to handle two different classes of clients.   Using  the  option
       space  definition  shown  in the previous example, you can send different option values to
       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 definitions all at once (even transmitted
       to the same client), so it is not necessary to configure this.

SEE ALSO

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

AUTHOR

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

                                                                                  dhcp-options(5)