Provided by: isc-dhcp-common_4.2.4-7ubuntu12.13_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.    This
       data  type  is  not  used for any existing DHCP options.   The domain name is stored just as if it were a
       text option.

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

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

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

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

SETTING OPTION VALUES USING EXPRESSIONS

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

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 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 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 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 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 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 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 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 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 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 1035) servers available to the client.
         Servers should be listed in order of preference.

       option nwip-domain string;

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

       option nwip-suboptions string;

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

       option path-mtu-aging-timeout uint32;

         This option specifies the timeout (in seconds) to use when aging Path  MTU  values  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 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 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 string;

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

       This option is not user configurable in the server.

       option swap-server ip-address;

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

       option tcp-keepalive-garbage flag;

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

       option tcp-keepalive-interval uint32;

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

       option tftp-server-name text;

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

       option time-offset int32;

         The time-offset option specifies the  offset  of  the  client's  subnet  in  seconds  from  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 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 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.hostname  will  be
         "example.com.".   If this suboption value is not set, it means that an unqualified name was sent in the
         fqdn option, or that no fqdn option was sent at all.

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

THE NETWARE/IP SUBOPTIONS

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

       option nwip.nsq-broadcast flag;

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

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

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

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

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

       option nwip.autoretries uint8;

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

       option nwip.autoretry-secs uint8;

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

       option nwip.nwip-1-1 uint8;

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

       option nwip.primary-dss ip-address;

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

STANDARD DHCPV6 OPTIONS

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

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

       option dhcp6.subscriber-id;

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

       option dhcp6.fqdn string;

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

       option dhcp6.lq-query string;

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

       option dhcp6.client-data string;

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

       option dhcp6.clt-time uint32;

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

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

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

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

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

DEFINING NEW OPTIONS

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

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

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

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

       New options are declared as follows:

       option new-name code new-code = definition ;

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

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

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

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

       INTEGER

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

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

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

       IP-ADDRESS

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

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

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

       IP6-ADDRESS

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

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

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

       TEXT

       option new-name code new-code = text ;

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

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

       DATA STRING

       option new-name code new-code = string ;

       An option whose type is a data string is essentially just a collection of bytes,  and  can  be  specified
       either as quoted text, like the text type, or as a list of hexadecimal 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 recieves an option that is compressed  and
       the  compressed  keyword is omitted, it will still decompress the option (relative to the option contents
       field).  The keyword only controls whether or not 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  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

       The Internet Systems Consortium DHCP Distribution was written by Ted Lemon under a  contract  with  Vixie
       Labs.   Funding  for  this  project  was provided through Internet Systems Consortium.  Information about
       Internet Systems Consortium can be found at https://www.isc.org.

                                                                                                 dhcp-options(5)