Provided by: isc-dhcp-common_4.4.3-P1-4ubuntu2_amd64 bug

NAME

       dhcp-options - Dynamic Host Configuration Protocol options

DESCRIPTION

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

REFERENCE: OPTION STATEMENTS

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

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

       The ip-address data  type  can  be  entered  either  as  an  explicit  IP  address  (e.g.,
       239.254.197.10)  or as a domain name (e.g., haagen.isc.org).  When entering a domain name,
       be sure that that domain name resolves to a single IP address. Additionally,  please  note
       the  software  (dhcpd  or dhclient) will only attempt to resolve the domain name the first
       time the option is needed. For example, if the next-server option is defined as  a  domain
       name,  dhcpd  will  attempt to resolve it while responding to the first client query dhcpd
       receives after startup. Should the domain's address subsequently change, the software  has
       to be restarted in order to pick up the change.

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

       The  int32 data type specifies a signed 32-bit integer.  The uint32 data type specifies an
       unsigned 32-bit integer.  The int16 and uint16 data  types  specify  signed  and  unsigned
       16-bit  integers.   The  int8  and  uint8  data  types  specify  signed and unsigned 8-bit
       integers.  Unsigned 8-bit integers are also sometimes referred to as octets.

       The text data type specifies an NVT ASCII string, which must be enclosed in double  quotes
       - for example, to specify a root-path option, the syntax would be

       option root-path "10.0.1.4:/var/tmp/rootfs";

       The  domain-name  data  type specifies a domain name, which must not be enclosed in double
       quotes.  The domain name is stored just as if it were a text option.

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

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

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

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

SETTING OPTION VALUES USING EXPRESSIONS

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

         option my-option = expression ;

       For example:

         option hostname = binary-to-ascii (16, 8, "-",
                                            substring (hardware, 1, 6));

INCLUDING OPTION DEFINITIONS

       Starting with 4.3.0 when ISC  adds  new  option  definitions  those  definitions  will  be
       included  in  the code based on the definition of an argument for the RFC that defines the
       option in includes/site.h.  This provides you  with  a  method  for  over-riding  the  ISC
       definitions  if  necessary  - for example if you have previously defined the option with a
       different format using the mechanism from DEFINING NEW OPTIONS below.

       By default all of the options are enabled.  In order to disable an option you  would  edit
       the includes/site.h file and comment out the definition for the proper RFC.

STANDARD DHCPV4 OPTIONS

       The  documentation  for  the various options mentioned below is taken from the latest IETF
       draft document on DHCP options.  Options not listed below may not yet be implemented,  but
       it is possible to use such options by defining them in the configuration file.  Please see
       the DEFINING NEW OPTIONS heading later in this document for more information.

       Some of the options documented here are automatically generated by the DHCP server  or  by
       clients, and cannot be configured by the user.  The value of such an option can be used in
       the configuration file of the receiving  DHCP  protocol  agent  (server  or  client),  for
       example in conditional expressions. However, the value of the option cannot be used in the
       configuration file of the sending agent, because the value is determined  only  after  the
       configuration  file  has been processed. In the following documentation, such options will
       be shown as "not user configurable"

       The standard options are:

       option all-subnets-local flag;

         This option specifies whether or not the client may assume that all subnets  of  the  IP
         network  to which the client is connected use the same MTU as the subnet of that network
         to which the client is directly connected.  A value of true indicates that  all  subnets
         share  the  same  MTU.   A  value of false means that the client should assume that some
         subnets of the directly connected network may have smaller MTUs.

       option arp-cache-timeout uint32;

         This option specifies the timeout in seconds for ARP cache entries.

       option associated-ip ip-address [, ip-address... ];

         This option is part of lease query.  It is used  to  return  all  of  the  IP  addresses
         associated with a given DHCP client.

         This option is not user configurable.

       option bcms-controller-address ip-address [, ip-address... ];

         This  option  configures  a  list  of  IPv4 addresses for use as Broadcast and Multicast
         Controller Servers ("BCMS").

       option bcms-controller-names domain-list;

         This option contains the domain  names  of  local  Broadcast  and  Multicast  Controller
         Servers ("BCMS") controllers which the client may use.

       option bootfile-name text;

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

       option boot-size uint16;

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

       option broadcast-address ip-address;

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

       option capwap-ac-v4 ip-address [, ip-address ... ] ;

         A  list  of IPv4 addresses of CAPWAP ACs that the WTP may use.  The addresses are listed
         in preference order.

         This option is included based on RFC 5417.

       option client-last-transaction-time uint32;

         This option is part of lease query.  It allows the receiver to determine the time of the
         most  recent  access  by  the  client.  The value is a duration in seconds from when the
         client last communicated with the DHCP server.

         This option is not user configurable.

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

         The cookie server option specifies a list of RFC 865 cookie  servers  available  to  the
         client.  Servers should be listed in order of preference.

       option default-ip-ttl uint8;

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

       option default-tcp-ttl uint8;

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

       option default-url string;

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

       option dhcp-client-identifier string;

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

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

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

         rather than:

              option dhcp-client-identifier "foo";

       option dhcp-lease-time uint32;

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

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

       option dhcp-max-message-size uint16;

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

       option dhcp-message text;

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

         This option is not user configurable.

       option dhcp-message-type uint8;

         This  option,  sent  by  both  client  and  server,  specifies  the type of DHCP message
         contained in the DHCP packet. Possible values (taken directly from RFC2132) are:

                      1     DHCPDISCOVER
                      2     DHCPOFFER
                      3     DHCPREQUEST
                      4     DHCPDECLINE
                      5     DHCPACK
                      6     DHCPNAK
                      7     DHCPRELEASE
                      8     DHCPINFORM

         This option is not user configurable.

       option dhcp-option-overload uint8;

         This option is used to indicate that  the  DHCP  ´sname´  or  ´file´  fields  are  being
         overloaded by using them to carry DHCP options. A DHCP server inserts this option if the
         returned parameters will exceed the usual space allotted for options.

         If this option is present, the client interprets the specified additional  fields  after
         it concludes interpretation of the standard option fields.

         Legal values for this option are:

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

         This option is not user configurable.

       option dhcp-parameter-request-list uint8 [, uint8... ];

         This  option,  when  sent  by  the client, specifies which options the client wishes the
         server to return.  Normally, in the ISC DHCP client, this  is  done  using  the  request
         statement.  If this option is not specified by the client, the DHCP server will normally
         return every option that is valid in scope and that fits  into  the  reply.   When  this
         option  is  specified on the server, the server returns the specified options.  This can
         be used to force a client to take options that it hasn't requested, and it can  also  be
         used  to tailor the response of the DHCP server for clients that may need a more limited
         set of options than those the server would normally return.

       option dhcp-rebinding-time uint32;

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

         This option is user configurable, but it will be ignored if the value is greater than or
         equal to the lease time.

         To make DHCPv4+DHCPv6 migration easier in the  future,  any  value  configured  in  this
         option is also used as a DHCPv6 "T1" (renew) time.

       option dhcp-renewal-time uint32;

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

         This option is user configurable, but it will be ignored if the value is greater than or
         equal to the rebinding time, or lease time.

         To  make  DHCPv4+DHCPv6  migration  easier  in  the future, any value configured in this
         option is also used as a DHCPv6 "T2" (rebind) time.

       option dhcp-requested-address ip-address;

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

         This option is not user configurable.

       option dhcp-server-identifier ip-address;

         This  option  is  used  in  DHCPOFFER  and  DHCPREQUEST  messages, and may optionally be
         included in the DHCPACK and DHCPNAK messages.  DHCP servers include this option  in  the
         DHCPOFFER  in  order  to  allow  the  client  to distinguish between lease offers.  DHCP
         clients use the contents of the ´server identifier´ field as the destination address for
         any  DHCP  messages  unicast  to  the  DHCP server.  DHCP clients also indicate which of
         several lease offers is being  accepted  by  including  this  option  in  a  DHCPREQUEST
         message.

         The value of this option is the IP address of the server.

         This  option  is not directly user configurable. See the server-identifier server option
         in dhcpd.conf(5).

       option domain-name text;

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

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

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

       option domain-search domain-list;

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

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

       option extensions-path text;

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

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

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

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

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

       option geoconf-civic string;

         A string to hold the geoconf civic structure.

         This option is included based on RFC 4776.

       option host-name string;

         This option specifies the name of the client.  The name may or may not be qualified with
         the  local  domain  name  (it is preferable to use the domain-name option to specify the
         domain name).  See RFC 1035 for character set restrictions.  This option is only honored
         by dhclient-script(8) if the hostname for the client machine is not set.

       option ieee802-3-encapsulation flag;

         This  option specifies whether or not the client should use Ethernet Version 2 (RFC 894)
         or IEEE 802.3 (RFC 1042) encapsulation if the interface is  an  Ethernet.   A  value  of
         false indicates that the client should use RFC 894 encapsulation.  A value of true means
         that the client should use RFC 1042 encapsulation.

       option ien116-name-servers ip-address [, ip-address...  ];

         The ien116-name-servers option specifies a list of IEN 116 name servers available to the
         client.  Servers should be listed in order of preference.

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

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

       option interface-mtu uint16;

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

       option ip-forwarding flag;

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

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

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

       option loader-configfile text

         This option is used to specify a boot loading configuration file  a  PXE  client  should
         use.

         This option is included based on RFC 5071.

       option loader-pathprefix text

         This option is used to specify a path prefix a PXE client should use in conjunction with
         the boot load configuration file.

         This option is included based on RFC 5071.

       option loader-reboottime uint32

         This option is used to dictate the maximum amount of time  a  PXE  client  should  allow
         itself to achieve configured network resources before rebooting.

         This option is included based on RFC 5071.

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

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

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

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

       option mask-supplier flag;

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

       option max-dgram-reassembly uint16;

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

       option merit-dump text;

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

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

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

       option name-service-search uint16 [, uint6... ];

         This option specifies a list of name services in the order the client should attempt  to
         use them.

         This option is included based on RFC 2937.

       option nds-context string;

         The  nds-context  option specifies the name of the initial Netware Directory Service for
         an NDS client.

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

         The nds-servers option specifies a list of IP addresses of NDS servers.

       option nds-tree-name string;

         The nds-tree-name option specifies NDS tree name that the NDS client should use.

       option netbios-dd-server ip-address [, ip-address...  ];

         The NetBIOS datagram distribution server (NBDD) option specifies a list of RFC 1001/1002
         NBDD servers listed in order of preference.

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

         The  NetBIOS  name  server  (NBNS)  option  specifies  a list of RFC 1001/1002 NBNS name
         servers listed in order of preference.  NetBIOS Name Service is currently more  commonly
         referred  to  as  WINS.   WINS  servers  can be specified using the netbios-name-servers
         option.

       option netbios-node-type uint8;

         The NetBIOS node type option allows NetBIOS over TCP/IP clients which  are  configurable
         to  be  configured  as  described  in RFC 1001/1002.  The value is specified as a single
         octet which identifies the client type.

         Possible node types are:

         1    B-node: Broadcast - no WINS

         2    P-node: Peer - WINS only

         4    M-node: Mixed - broadcast, then WINS

         8    H-node: Hybrid - WINS, then broadcast

       option netbios-scope string;

         The NetBIOS scope option specifies the NetBIOS  over  TCP/IP  scope  parameter  for  the
         client  as  specified in RFC 1001/1002. See RFC1001, RFC1002, and RFC1035 for character-
         set restrictions.

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

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

       option netinfo-server-tag text;

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

       option nis-domain text;

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

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

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

       option nisplus-domain text;

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

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

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

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

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

       option non-local-source-routing flag;

         This option specifies whether  the  client  should  configure  its  IP  layer  to  allow
         forwarding  of  datagrams  with  non-local source routes (see Section 3.3.5 of [4] for a
         discussion of this  topic).   A  value  of  false  means  disallow  forwarding  of  such
         datagrams, and a value of true means allow forwarding.

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

         This option specifies a list of IP addresses indicating NTP (RFC 5905) servers available
         to the client.  Servers should be listed in order of preference.

       option nwip-domain string;

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

       option nwip-suboptions string;

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

       option pxe-system-type uint16 [, uint16 ... ];

         A list of one ore more 16-bit integers which allows a client  to  specify  its  pre-boot
         architecture type(s).

         This option is included based on RFC 4578.

       option pxe-interface-id uint8 uint8 uint8

         A three octet value which allows a client to specify its network interface type.

         This option is included based on RFC 4578.

       option pxe-client-id uint8 string

         A single octet indicating type, followed by a string that allows a client to specify its
         PXE client identity.

         This option is included based on RFC 4578.

       option option-6rd uint8 uint8 ip6-address ip-address [, ip-address ...];

         This option contains information about the rapid deployment option.  It  is  8  bits  of
         ipv4  mask  length, 8 bits of 6rd prefix length, an ipv6 prefix as an ipv6 address and a
         list of one or more ipv4 addresses.

         This option is included based on RFC 5969.

       option pana-agent ip-address [, ip-address ... ] ;

         A set of IPv4 addresses of a PAA for the client to use.  The  addresses  are  listed  in
         preferred order.

         This option is included based on RFC 5192.

       option path-mtu-aging-timeout uint32;

         This  option  specifies  the  timeout  (in  seconds)  to  use when aging Path MTU values
         discovered by the mechanism defined in RFC 1191.

       option path-mtu-plateau-table uint16 [, uint16...  ];

         This option specifies a table of MTU sizes to use when performing Path MTU Discovery  as
         defined  in  RFC  1191.   The  table is formatted as a list of 16-bit unsigned integers,
         ordered from smallest to largest.  The minimum MTU value cannot be smaller than 68.

       option pcode text;

         This option specifies a string suitable for the TZ variable.

         This option is included based on RFC 4833.

       option perform-mask-discovery flag;

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

       option policy-filter ip-address ip-address
                         [, ip-address ip-address...];

         This option specifies policy filters for non-local source routing.  The filters  consist
         of  a  list of IP addresses and masks which specify destination/mask pairs with which to
         filter incoming source routes.

         Any source routed datagram whose next-hop address does not  match  one  of  the  filters
         should be discarded by the client.

         See STD 3 (RFC1122) for further information.

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

         The  POP3  server  option  specifies  a  list  of  POP3 servers available to the client.
         Servers should be listed in order of preference.

       option rdnss-selection uint8 ip-address ip-address domain-name;

         The rdnss-selection option specifies an 8 bit flags field, a primary  and  secondary  ip
         address  for the name server and a domainlist of domains for which the RDNSS has special
         knowledge.

         This option is included based on RFC 6731.

       option resource-location-servers ip-address
                                     [, ip-address...];

         This option specifies a list of RFC 887  Resource  Location  servers  available  to  the
         client.  Servers should be listed in order of preference.

       option root-path text;

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

       option router-discovery flag;

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

       option router-solicitation-address ip-address;

         This  option  specifies  the  address  to  which  the  client  should  transmit   router
         solicitation requests.

       option routers ip-address [, ip-address...  ];

         The  routers option specifies a list of IP addresses for routers on the client's subnet.
         Routers should be listed in order of preference.

       option slp-directory-agent boolean ip-address [, ip-address... ];

         This option specifies two things: the IP addresses  of  one  or  more  Service  Location
         Protocol  Directory Agents, and whether the use of these addresses is mandatory.  If the
         initial boolean value is true, the SLP agent should just use the IP addresses given.  If
         the  value  is  false,  the  SLP  agent  may additionally do active or passive multicast
         discovery of SLP agents (see RFC2165 for details).

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

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

       option slp-service-scope boolean text;

         The Service Location Protocol Service Scope Option  specifies  two  things:  a  list  of
         service  scopes  for SLP, and whether the use of this list is mandatory.  If the initial
         boolean value is true, the SLP agent should only use the list of scopes provided in this
         option;  otherwise,  it  may  use its own static configuration in preference to the list
         provided in this option.

         The text string should be a comma-separated list of scopes that  the  SLP  agent  should
         use.   It  may  be  omitted, in which case the SLP Agent will use the aggregated list of
         scopes of all directory agents known to the SLP agent.

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

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

       option static-routes ip-address ip-address
                         [, ip-address ip-address...];

         This  option  specifies  a  list  of static routes that the client should install in its
         routing cache.  If multiple routes to the  same  destination  are  specified,  they  are
         listed in descending order of priority.

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

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

       option streettalk-directory-assistance-server ip-address
                                                  [, ip-address...];

         The  StreetTalk  Directory  Assistance  (STDA)  server  option  specifies a list of STDA
         servers available to the client.  Servers should be listed in order of preference.

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

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

       option subnet-mask ip-address;

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

       option subnet-selection ip-address;

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

       This option is not user configurable in the server.

       option swap-server ip-address;

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

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

         This option configures a list of one or more IPv4 addresses of tftp servers a client may
         use.

         This option is included based on RFC 5859

       option tcp-keepalive-garbage flag;

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

       option tcp-keepalive-interval uint32;

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

       option tcode text;

         This option specifies a name of a zone entry in the TZ database.

         This option is included based on RFC 4833.

       option tftp-server-name text;

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

       option time-offset int32;

         The time-offset option specifies the offset of  the  client's  subnet  in  seconds  from
         Coordinated Universal Time (UTC).

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

         The time-server option specifies a list of RFC 868 time servers available to the client.
         Servers should be listed in order of preference.

       option trailer-encapsulation flag;

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

       option uap-servers text;

         This  option  specifies  a  list of URLs, each pointing to a user authentication service
         that  is  capable  of  processing  authentication  requests  encapsulated  in  the  User
         Authentication  Protocol  (UAP).   UAP  servers  can  accept  either  HTTP  1.1 or SSLv3
         connections.  If the list includes a URL that does not contain  a  port  component,  the
         normal  default port is assumed (i.e., port 80 for http and port 443 for https).  If the
         list includes a URL that does not contain a path component, the path  /uap  is  assumed.
         If more than one URL is specified in this list, the URLs are separated by spaces.

       option user-class string;

         This  option  is  used  by  some  DHCP clients as a way for users to specify identifying
         information to the client.  This can be used in  a  similar  way  to  the  vendor-class-
         identifier option, but the value of the option is specified by the user, not the vendor.
         Most recent DHCP clients have a way in the user interface to specify the value for  this
         identifier, usually as a text string.

       option v4-access-domain domain-name;

         The domain name associated with the access network for use with LIS Discovery.

         This option is included based on RFC 5986.

       option v4-lost domain-name;

         The domain name of the LoST server for the client to use.

         This option is included based on RFC 5223.

       option v6-only-preferred uint32;

         The number of seconds the client should disable DHCPv4 for.

         This option and its use by the client are specified in RFC 8925.

       option vendor-class-identifier string;

         This  option  is  used by some DHCP clients to identify the vendor type and possibly the
         configuration of a DHCP client.  The information is a string of bytes whose contents are
         specific  to  the  vendor and are not specified in a standard.  To see what vendor class
         identifier clients are sending,  you  can  write  the  following  in  your  DHCP  server
         configuration file:

         set vendor-string = option vendor-class-identifier;

         This  will result in all entries in the DHCP server lease database file for clients that
         sent vendor-class-identifier options having a set statement that  looks  something  like
         this:

         set vendor-string = "SUNW.Ultra-5_10";

         The  vendor-class-identifier option is normally used by the DHCP server to determine the
         options that are returned in the vendor-encapsulated-options  option.   Please  see  the
         VENDOR ENCAPSULATED OPTIONS section later in this manual page for further information.

       option vendor-encapsulated-options string;

         The vendor-encapsulated-options option can contain either a single vendor-specific value
         or one or more vendor-specific suboptions.  This option is not normally specified in the
         DHCP  server  configuration  file  - instead, a vendor class is defined for each vendor,
         vendor class suboptions are defined, values for those suboptions are  defined,  and  the
         DHCP server makes up a response on that basis.

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

       option vivso string;

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

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

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

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

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

RELAY AGENT INFORMATION OPTION

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

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

       option agent.circuit-id string;

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

       option agent.remote-id string;

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

       option agent.DOCSIS-device-class uint32;

         The DOCSIS-device-class suboption is intended  to  convey  information  about  the  host
         endpoint,  hardware,  and  software,  that  either the host operating system or the DHCP
         server may not otherwise be aware of (but the relay is able to  distinguish).   This  is
         implemented  as  a  32-bit field (4 octets), each bit representing a flag describing the
         host in one of these ways.  So far, only bit zero (being the least significant  bit)  is
         defined  in RFC3256.  If this bit is set to one, the host is considered a CPE Controlled
         Cable Modem (CCCM).  All other bits are reserved.

       option agent.link-selection ip-address;

         The link-selection suboption is provided by relay agents to inform servers  what  subnet
         the  client  is  actually  attached  to.  This is useful in those cases where the giaddr
         (where responses must be sent to the relay agent) is not  on  the  same  subnet  as  the
         client.   When  this  option  is present in a packet from a relay agent, the DHCP server
         will use its contents to find a subnet declared in configuration, and from here take one
         step  further  backwards  to  any  shared-network  the subnet may be defined within; the
         client may be given any address within that shared network, as normally appropriate.

THE CLIENT FQDN SUBOPTIONS

       The Client FQDN option, currently  defined  in  the  Internet  Draft  draft-ietf-dhc-fqdn-
       option-00.txt  is not a standard yet, but is in sufficiently wide use already that we have
       implemented it.  Due to the complexity of the option format, we have implemented it  as  a
       suboption  space  rather  than  a  single  option.   In  general this option should not be
       configured by the user - instead it should be used as part  of  an  automatic  DNS  update
       system.

       option fqdn.no-client-update flag;

         When  the  client  sends  this,  if  it is true, it means the client will not attempt to
         update its A record.  When sent by the server to the client, it means  that  the  client
         should not update its own A record.

       option fqdn.server-update flag;

         When  the client sends this to the server, it is requesting that the server update its A
         record.  When sent by the server, it means that the server has updated (or is  about  to
         update) the client's A record.

       option fqdn.encoded flag;

         If  true,  this  indicates that the domain name included in the option is encoded in DNS
         wire format, rather than as plain ASCII text.  The client normally sets this to false if
         it  doesn't  support  DNS wire format in the FQDN option.  The server should always send
         back the same value that the client sent.  When this value is set on  the  configuration
         side, it controls the format in which the fqdn.fqdn suboption is encoded.

       option fqdn.rcode1 flag;

       option fqdn.rcode2 flag;

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

       option fqdn.fqdn text;

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

       option fqdn.hostname --never set--;

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

       option fqdn.domainname --never set--;

         This  option  should  never be set, but it can be read back using the option and config-
         option operators in an expression, in which case it returns all labels after  the  first
         label  in  the  fqdn.fqdn  suboption  -  for  example,  if  the  value  of  fqdn.fqdn is
         "foo.example.com.", then fqdn.domainname will  be  "example.com.".   If  this  suboption
         value is not set, it means that an unqualified name was sent in the fqdn option, or that
         no fqdn option was sent at all.

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

THE NETWARE/IP SUBOPTIONS

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

       option nwip.nsq-broadcast flag;

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

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

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

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

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

       option nwip.autoretries uint8;

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

       option nwip.autoretry-secs uint8;

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

       option nwip.nwip-1-1 uint8;

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

       option nwip.primary-dss ip-address;

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

STANDARD DHCPV6 OPTIONS

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

       option dhcp6.client-id string;

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

         duid-llt

         duid-en

         duid-ll

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

       option dhcp6.server-id string;

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

       option dhcp6.ia-na string;

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

       option dhcp6.ia-ta string;

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

       option dhcp6.ia-addr string;

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

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

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

       option dhcp6.preference uint8;

         The preference option informs a DHCPv6 client which server is ´preferred´ for use  on  a
         given   subnet.    This  preference  is  only  applied  during  the  initial  stages  of
         configuration - once a client is bound to an IA, it will remain bound to that  IA  until
         it  is  no longer valid or has expired.  This value may be configured on the server, and
         is digested by the client software.

       option dhcp6.elapsed-time uint16;

         The elapsed-time option is constructed by the DHCPv6 client software, and is potentially
         consumed by intermediaries.  This option should not be configured.

       option dhcp6.relay-msg string;

         The  relay-msg  option  is constructed by intervening DHCPv6 relay agent software.  This
         option is entirely used by protocol software, and is not meant for user configuration.

       option dhcp6.unicast ip6-address;

         The unicast option is provided by DHCPv6  servers  which  are  willing  (or  prefer)  to
         receive  Request,  Renew,  Decline,  and Release packets from their clients via unicast.
         Normally, DHCPv6 clients will multicast these messages.  Per RFC 3315, the  server  will
         reject a unicast message received from a client unless it previously sent (or would have
         sent) the unicast option to that client.  This option may be configured on the server at
         the  global  and  shared  network level.  When a unicast message is received, the server
         will check for an applicable definition of the unicast option.  If  such  an  option  is
         found the message will be accepted, if not it will be rejected.

       option dhcp6.status-code status-code [ string ] ;

         The  status-code  option  is  provided  by  DHCPv6  servers  to  inform clients of error
         conditions during protocol communication.  This option is manufactured and  digested  by
         protocol software, and should not be configured.

       option dhcp6.rapid-commit ;

         The  rapid-commit  option  is  a  zero-length  option that clients use to indicate their
         desire to enter into rapid-commit with the server.

       option dhcp6.vendor-opts string;

         The vendor-opts option is actually an  encapsulated  sub-option  space,  in  which  each
         Vendor-specific  Information  Option  (VSIO)  is  identified  by  a 32-bit Enterprise-ID
         number.  The encapsulated option spaces within these options are defined by the vendors.

         To make use of this option, the best  way  is  to  examine  the  section  titled  VENDOR
         ENCAPSULATED OPTIONS below, in particular the bits about the "vsio" option space.

       option dhcp6.interface-id string;

         The  interface-id  option  is  manufactured  by  relay  agents, and may be used to guide
         configuration differentiating clients by the interface they are  remotely  attached  to.
         It  does  not  make sense to configure a value for this option, but it may make sense to
         inspect its contents.

       option dhcp6.reconf-msg dhcpv6-message;

         The reconf-msg option is manufactured by servers, and sent  to  clients  in  Reconfigure
         messages  to  inform them of what message the client should Reconfigure using.  There is
         no  support  for  DHCPv6  Reconfigure  extensions,  and  this   option   is   documented
         informationally only.

       option dhcp6.reconf-accept ;

         The  reconf-accept  option  is  included  by DHCPv6 clients that support the Reconfigure
         extensions, advertising that they will respond  if  the  server  were  to  ask  them  to
         Reconfigure.   There is no support for DHCPv6 Reconfigure extensions, and this option is
         documented informationally only.

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

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

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

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

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

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

       option dhcp6.domain-search domain-list;

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

       option dhcp6.ia-pd string;

         The  ia-pd  option  is manufactured by clients and servers to create a Prefix Delegation
         binding - to delegate an IPv6 prefix to the  client.   It  is  not  directly  edited  in
         dhcpd.conf(5)  or  dhclient.conf(5),  but  rather  is  manufactured  and consumed by the
         software.

       option dhcp6.ia-prefix string;

         The ia-prefix option is placed inside ia-pd options in order to identify the  prefix(es)
         allocated   to   the   client.    It   is   not  directly  edited  in  dhcpd.conf(5)  or
         dhclient.conf(5), but rather is manufactured and consumed by the software.

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

         The nis-servers option identifies, in order, NIS servers available to the client.

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

         The nisp-servers option identifies, in order, NIS+ servers available to the client.

       option nis-domain-name domain-list;

         The nis-domain-name option specifies the NIS domain name the client is expected to  use,
         and is related to the nis-servers option.

       option dhcp6.nis-domain-name domain-name;

         The  dhcp6.nis-domain-name  option  specifies  NIS domain name the client is expected to
         use, and is related to dhcp6.nis-servers option.

       option nisp-domain-name domain-list;

         The nisp-domain-name option specifies the NIS+ domain name the  client  is  expected  to
         use, and is related to the nisp-servers option.

       option dhcp6.nisp-domain-name domain-name;

         The  dhcp6.nis-domain-name  option  specifies NIS+ domain name the client is expected to
         use, and is related to dhcp6.nisp-servers option.

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

         The sntp-servers option specifies a list of local SNTP servers available for the  client
         to synchronize their clocks.

       option dhcp6.info-refresh-time uint32;

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

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

         The bcms-server-d option  contains  the  domain  names  of  local  BCMS  (Broadcast  and
         Multicast Control Services) controllers which the client may use.

       option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;

         The  bcms-server-a  option  contains  the  IPv6  addresses  of local BCMS (Broadcast and
         Multicast Control Services) controllers which the client may use.

       option dhcp6.geoconf-civic string;

         A string to hold the geoconf civic structure.

         This option is included based on RFC 4776.

       option dhcp6.remote-id string;

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

       option dhcp6.subscriber-id string;

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

       option dhcp6.fqdn string;

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

       option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;

         A set of IPv6 addresses of a PAA for the client to use.  The  addresses  are  listed  in
         preferred order.

         This option is included based on RFC 5192.

       option dhcp6.new-posix-timezone text;

         This option specifies a string suitable for the TZ variable.

         This option is included based on RFC 4833.

       option dhcp6.new-tzdb-timezone text;

         This option specifies a name of a zone entry in the TZ database.

         This option is included based on RFC 4833.

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

         A list of the options requested by the relay agent.

         This option is included based on RFC 4994.

       option dhcp6.lq-query string;

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

       option dhcp6.client-data string;

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

       option dhcp6.clt-time uint32;

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

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

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

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

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

       option dhcp6.v6-lost domain-name;

         The domain name of the LoST server for the client to use.

         This option is included based on RFC 5223.

       option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;

         A  list  of IPv6 addresses of CAPWAP ACs that the WTP may use.  The addresses are listed
         in preference order.

         This option is included based on RFC 5417.

       option dhcp6.relay-id string;

         The DUID for the relay agent.

         This option is included based on RFC 5460.

       option dhcp6.v6-access-domain domain-name;

         The domain name associated with the access network for use with LIS Discovery.

         This option is included based on RFC5986.

       option dhcp6.sip-ua-cs-list domain-list;

         The list of domain names in the SIP User Agent Configuration Service Domains.

         This option is included based on RFC 6011.

       option dhcp6.bootfile-url text;

         The URL for a boot file.

         This option is included based on RFC 5970.

       option dhcp6.bootfile-param string;

         A string for the parameters to the bootfile.  See RFC 5970 for more description  of  the
         layout of the parameters within the string.

         This option is included based on RFC 5970.

       option dhcp6.client-arch-type uint16 [, uint16 ... ] ;

         A list of one or more architecture types described as 16 bit values.

         This option is included based on RFC 5970.

       option dhcp6.nii uint8 uint8 uint8;

         The  client  network  interface  identitier option supplies information about a client's
         level of UNDI support.  The values are, in order, the type,  the  major  value  and  the
         minor value.

         This option is included based on RFC5970.

       option dhcp6.aftr-name domain-name;

         A domain name of the AFTR tunnel endpoint.

         This option is included based on RFC 6334.

       option dhcp6.erp-local-domain-name domain-name;

         A domain name for the ERP domain.

         This option is included based on RFC 6440.

       option dhcp6.rdnss-selection ip6-address uint8 domain-name;

         RDNSS  information  consists  of  an  IPv6  address of RDNSS, an 8 bit flags field and a
         domain-list of domains for which the RDNSS has special knowledge.

         This option is included based on RFC 6731.

       option dhcp6.client-linklayer-addr string;

         A client link-layer address.  The first two bytes must be the  type  of  the  link-layer
         followed by the address itself.

         This option is included based on RFC 6939.

       option dhcp6.link-address ip6-address;

         An  IPv6  address  used by a relay agent to indicate to the server the link on which the
         client is located.

         This option is included based on RFC 6977.

       option dhcp6.solmax-rt uint32;

         A value to override the default for SOL_MAX_RT.  This is a 32 bit value.

         This option is included based on RFC 7083.

       option dhcp6.inf-max-rt uint32;

         A value to override the default for INF_MAX_RT.  This is a 32 bit value.

         This option is included based on RFC 7083.

ACCESSING DHCPV6 RELAY OPTIONS

       v6relay (relay-number, option) This option allows access to an option that has been  added
       to  a packet by a relay agent.  Relay-number value selects the relay to examine and option
       is the option to find.  In DHCPv6 each relay encapsulates the entire previous message into
       an  option, adds its own options (if any) and sends the result onwards.  The RFC specifies
       a limit of 32 hops.  A relay-number of 0 is a no-op and means don't look at the relays.  1
       is  the relay that is closest to the client, 2 would be the next in from the client and so
       on.  Any value greater than the max number of hops is  which  is  closest  to  the  server
       independent  of  number.  To use this option in a class statement you would have something
       like this:

       match if v6relay(1, option dhcp6.subscriber-id) = "client_1";

DEFINING NEW OPTIONS

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

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

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

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

       New options are declared as follows:

       option new-name code new-code = definition ;

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

       The following simple option type definitions are supported:

       BOOLEAN

       option new-name code new-code = boolean ;

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

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

       INTEGER

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

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

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

       IP-ADDRESS

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

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

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

       IP6-ADDRESS

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

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

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

       TEXT

       option new-name code new-code = text ;

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

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

       DATA STRING

       option new-name code new-code = string ;

       An option whose type is a data string is essentially just a collection of bytes,  and  can
       be  specified  either  as  quoted  text,  like  the text type, or as a list of hexadecimal
       contents separated by colons whose values must be between 0 and FF.  For example:

       option sql-identification-token code 195 = string;
       option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;

       DOMAIN-LIST

       option new-name code new-code = domain-list [compressed] ;

       An option whose type is domain-list is an RFC1035 formatted (on the  wire,  "DNS  Format")
       list of domain names, separated by root labels.  The optional compressed keyword indicates
       if the option should be compressed relative to the start of the option contents  (not  the
       packet contents).

       When  in doubt, omit the compressed keyword.  When the software receives an option that is
       compressed and the compressed keyword is omitted, it  will  still  decompress  the  option
       (relative  to  the  option  contents  field).   The  keyword  only controls whether or not
       transmitted packets are compressed.

       Note that when domain-list formatted  options  are  output  as  environment  variables  to
       dhclient-script(8), the standard DNS -escape mechanism is used: they are decimal.  This is
       appropriate for direct use in eg /etc/resolv.conf.

       ENCAPSULATION

       option new-name code new-code = encapsulate identifier ;

       An option whose type is encapsulate will encapsulate the  contents  of  the  option  space
       specified  in  identifier.   Examples  of  encapsulated options in the DHCP protocol as it
       currently exists include the vendor-encapsulated-options  option,  the  netware-suboptions
       option and the relay-agent-information option.

       option space local;
       option local.demo code 1 = text;
       option local-encapsulation code 197 = encapsulate local;
       option local.demo "demo";

       ARRAYS

       Options  can  contain arrays of any of the above types except for the text and data string
       types, which aren't currently supported in arrays.  An example of an array  definition  is
       as follows:

       option kerberos-servers code 200 = array of ip-address;
       option kerberos-servers 10.20.10.1, 10.20.11.1;

       RECORDS

       Options  can also contain data structures consisting of a sequence of data types, which is
       sometimes called a record type.  For example:

       option contrived-001 code 201 = { boolean, integer 32, text };
       option contrived-001 on 1772 "contrivance";

       It's also possible to have options that are arrays of records, for example:

       option new-static-routes code 201 = array of {
            ip-address, ip-address, ip-address, integer 8 };
       option static-routes
            10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
            10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
            10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;

VENDOR ENCAPSULATED OPTIONS

       The DHCP protocol defines the vendor-encapsulated-options option, which allows vendors  to
       define  their  own  options  that will be sent encapsulated in a standard DHCP option.  It
       also defines the Vendor Identified Vendor Sub Options option  ("VIVSO"),  and  the  DHCPv6
       protocol  defines  the  Vendor-specific Information Option ("VSIO").  The format of all of
       these options is usually internally a string of options, similarly to  other  normal  DHCP
       options.   The  VIVSO and VSIO options differ in that they contain options that correspond
       to vendor Enterprise-ID numbers (assigned by IANA), which then contain  options  according
       to each Vendor's specifications.  You will need to refer to your vendor's documentation in
       order to form options to their specification.

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

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

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

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

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

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

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

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

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

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

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

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

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

       Once  you  have  defined  an  option  space and the format of some options, you can set up
       scopes that define values for those options, and you  can  say  when  to  use  them.   For
       example,  suppose  you  want to handle two different classes of clients.  Using the option
       space definition shown in the previous example, you can send different  option  values  to
       different  clients  based  on the vendor-class-identifier option that the clients send, as
       follows:

       class "vendor-classes" {
         match option vendor-class-identifier;
       }

       subclass "vendor-classes" "SUNW.Ultra-5_10" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/sparc";
       }

       subclass "vendor-classes" "SUNW.i86pc" {
         vendor-option-space SUNW;
         option SUNW.root-path "/export/root/i86pc";
       }

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

       option vivso-sample.sample "Hello world!";

       option docsis.tftp-servers ::1;

       As you can see in the preceding example, regular scoping rules apply, so  you  can  define
       values  that are global in the global scope, and only define values that are specific to a
       particular class in the local scope.  The vendor-option-space declaration tells  the  DHCP
       server  to  use  options  in  the  SUNW  option  space  to  construct  the  DHCPv4 vendor-
       encapsulated-options option.  This is a limitation of that option - the DHCPv4  VIVSO  and
       the DHCPv6 VSIO options can have multiple vendor definitions all at once (even transmitted
       to the same client), so it is not necessary to configure this.

SEE ALSO

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

AUTHOR

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

                                                                                  dhcp-options(5)