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dhcpd-options(5)                                              dhcpd-options(5)



NAME
       dhcp-options - Dynamic Host Configuration Protocol options

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

REFERENCE: OPTION STATEMENTS
       DHCP option statements always start with the option keyword, followed by an option  name,  followed  by  option
       data.  The option names and data formats are described below.   It is not necessary to exhaustively 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;

       The destination-descriptor describe the IP subnet number and subnet mask of a particular  destination  using  a
       compact  encoding. This encoding consists of one octet describing the width of the subnet mask, followed by all
       the significant octets of the subnet number.  The following table contains some examples of how various  subnet
       number/mask combinations can be encoded:

       Subnet number   Subnet mask      Destination descriptor
       0               0                0
       10.0.0.0        255.0.0.0        8.10
       10.0.0.0        255.255.255.0    24.10.0.0
       10.17.0.0       255.255.0.0      16.10.17
       10.27.129.0     255.255.255.0    24.10.27.129
       10.229.0.128    255.255.255.128  25.10.229.0.128
       10.198.122.47   255.255.255.255  32.10.198.122.47

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 defin-
       ing  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  con-
          nected.   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") con-
          trollers 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 inter-
          pretation 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.   Nor-
          mally,  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  transi-
          tions 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 transi-
          tions 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 distin-
          guish between lease offers.  DHCP clients use the contents of the 'server identifier' field as the  destina-
          tion  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 avail-
          able 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  charac-
          ter  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 mini-
          mum 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 char-
          acter 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 pro-
          tocol.

          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  omit-
          ted, 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 mul-
          tiple 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.

          NOTE to Fedora dhclient users:
          dhclient-script  interprets  trailing 0 octets of the target as indicating the subnet class of the route, so
          for the following static-routes value:
                  option static-routes 172.0.0.0 172.16.2.254,
                                       192.168.0.0 192.168.2.254;
          dhclient-script will create routes:
                  172/8 via 172.16.2.254 dev $interface
                  192.168/16 via 192.168.2.254 dev $interface

       option classless-static-routes destination-descriptor ip-address
                                   [, destination-descriptor ip-address...];

          This option (see RFC3442) specifies a list of classless static routes that the client should install in  its
          routing cache.

          This  option  can  contain one or more static routes, each of which consists of a destination descriptor and
          the IP address of the router that should be used to reach that destination.

          Many clients may not implement the Classless Static Routes option.  DHCP server administrators should there-
          fore  configure  their  DHCP  servers to send both a Router option and a Classless Static Routes option, and
          should specify the default router(s) both in the Router option and in the Classless Static Routes option.

          If the DHCP server returns both a Classless Static Routes option  and  a  Router  option,  the  DHCP  client
          ignores the Router option.

       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 pro-
          vided 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 pro-
          cessing  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 compo-
          nent,  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  fol-
          lowing 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 ven-
          dor-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 ENCAP-
          SULATED 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 cir-
          cuit.   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 actu-
          ally 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 sys-
       tem.

       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 speci-
          fication.

       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 exam-
          ple, 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 compari-
       son, 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  follow-
       ing 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 Net-
          Ware 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  mul-
       tiple options would be concatenated to form one option, in DHCPv6 they are expected to be individual instantia-
       tions.  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  tempo-
          rary  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 con-
          figured.

       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 applied during the initial stages of configu-
          ration - 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 inter-
          mediaries.  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  Informa-
          tion  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 differenti-
          ating 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 Recon-
          figure 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 out-
          bound 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.  There is not yet any support for prefix delegation in this software, and this
          option is provided informationally only.

       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.  There is not yet any suport for prefix delegation in this software, and  this  option  is  provided
          informationally only.

       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 deliv-
          ered 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 Ser-
          vices) 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 informa-
          tion 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.


       option dhcp6.bootfile-url string ;

          The server sends this option to inform the client about a URL to a boot file.  Used primarily for UEFI  net-
          work  booting,  it  contains  an RFC3986 compliant URI which the client may use to boot an operating system.
          This option is defined in RFC5970


       option dhcp6.arch-type arch-id [, arch-id...]  ;

          A client will send this option to a server so that the  server  may  make  decisions  on  what  options  and
          addresses to offer the requesting client.  The option consists of a list of 16 bit unsigned values that rep-
          resent the architecture of the requesting client.  These values corespond to the  values  available  to  the
          dhcpv4 option architecture-type, as defined in RFC4578, section 2.1.  This option is defined in RFC5970


       option dhcp6.net-id uint8 uint8 uint8 ;

          A client will send this option to a server to inform it about the clients level of UNDI support.  The option
          consists of 3 octets (a type, major and minor value).  Specific meanings of these values  are  doumented  in
          section 2.2 of RFC4578.  This option is defined in RFC5970


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 con-
       tents 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 docu-
       mented 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 confi-
       dence 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 cur-
       rently 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-con-
       nection-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  rela-
       tive 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 Enter-
       prise-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 Ven-
       dor 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  rele-
       vant 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 fol-
       lows:

       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.



                                                              dhcpd-options(5)