Provided by: dhcp3-common_3.0.6.dfsg-1ubuntu9_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  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
       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 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 DHCP 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 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 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;

          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 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 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 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.

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  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.

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.   For  site-local
       options,  all  codes between 128 and 254 are reserved for DHCP options,
       so you can pick any one of  these.   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, but it’s not likely to cause too much trouble in practice.

       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;

       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;

       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.   The format of the vendor-
       encapsulated-options option is either a series of bytes whose format is
       not  specified,  or  a sequence of options, each of which consists of a
       single-byte vendor-specific option  code,  followed  by  a  single-byte
       length,  followed  by  as  many  bytes  of data as are specified in the
       length (the length does not include itself or the option code).

       The value of this option 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 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;

       The second way of setting the value of this option 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  vendor-encapsulated-options
       option.

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

       option space name ;

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

       option space SUNW;
       option SUNW.server-address code 2 = ip-address;
       option SUNW.server-name code 3 = text;
       option SUNW.root-path code 4 = text;

       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;
       }

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

       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";
       }

       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  vendor-
       encapsulated-options option.

SEE ALSO

       dhcpd.conf(5),   dhcpd.leases(5),    dhclient.conf(5),    dhcp-eval(5),
       dhcpd(8),    dhclient(8),   RFC2132,   RFC2131,   draft-ietf-dhc-agent-
       options-??.txt.

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 http://www.isc.org.

                                                              dhcpd-options(5)