Provided by: isc-dhcp-common_4.1.ESV-R4-0ubuntu5_i386 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 not user configurable.

       option dhcp-renewal-time uint32;

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

         This option is not user configurable.

       option dhcp-requested-address ip-address;

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

         This option is not user configurable.

       option dhcp-server-identifier ip-address;

         This option is used in DHCPOFFER and DHCPREQUEST  messages,  and  may
         optionally  be  included  in  the DHCPACK and DHCPNAK messages.  DHCP
         servers include this option in the DHCPOFFER in order  to  allow  the
         client  to  distinguish  between  lease offers.  DHCP clients use the
         contents of the 'server identifier' field as the destination  address
         for  any DHCP messages unicast to the DHCP server.  DHCP clients also
         indicate which of 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.
         This  option  is  not  supported  by  the client at this time, and is
         digested by the server when present, so should not be configured.

       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 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.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)