1dhcp-options(5) File Formats Manual dhcp-options(5)
2
6 dhcp-options - Dynamic Host Configuration Protocol options
7
9 The Dynamic Host Configuration protocol allows the client to receive
10 options from the DHCP server describing the network configuration and
11 various services that are available on the network. When configuring
12 dhcpd(8) or dhclient(8) , options must often be declared. The syntax
13 for declaring options, and the names and formats of the options that
14 can be declared, are documented here.
15
17 DHCP option statements always start with the option keyword, followed
18 by an option name, followed by option data. The option names and data
19 formats are described below. It is not necessary to exhaustively spec‐
20 ify all DHCP options - only those options which are needed by clients
21 must be specified.
22 Option data comes in a variety of formats, as defined below:
24 The ip-address data type can be entered either as an explicit IP
26 address (e.g., 239.254.197.10) or as a domain name (e.g., haa‐
27 gen.isc.org). When entering a domain name, be sure that that domain
28 name resolves to a single IP address.
29 The ip6-address data specifies an IPv6 address, like ::1 or
31 3ffe:bbbb:aaaa:aaaa::1.
32 The int32 data type specifies a signed 32-bit integer. The uint32 data
34 type specifies an unsigned 32-bit integer. The int16 and uint16 data
35 types specify signed and unsigned 16-bit integers. The int8 and uint8
36 data types specify signed and unsigned 8-bit integers. Unsigned 8-bit
37 integers are also sometimes referred to as octets.
38 The text data type specifies an NVT ASCII string, which must be
40 enclosed in double quotes - for example, to specify a root-path option,
41 the syntax would be
42 option root-path "10.0.1.4:/var/tmp/rootfs";
44 The domain-name data type specifies a domain name, which must not be
46 enclosed in double quotes. The domain name is stored just as if it
47 were a text option.
48 The domain-list data type specifies a list of domain names, enclosed in
50 double quotes and separated by commas ("example.com", "foo.exam‐
51 ple.com").
52 The flag data type specifies a boolean value. Booleans can be either
54 true or false (or on or off, if that makes more sense to you).
55 The string data type specifies either an NVT ASCII string enclosed in
57 double quotes, or a series of octets specified in hexadecimal, sepa‐
58 rated by colons. For example:
59 option dhcp-client-identifier "CLIENT-FOO";
61 or
62 option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f;
63 The destination-descriptor describe the IP subnet number and subnet
65 mask of a particular destination using a compact encoding. This encod‐
66 ing consists of one octet describing the width of the subnet mask, fol‐
67 lowed by all the significant octets of the subnet number. The follow‐
68 ing table contains some examples of how various subnet number/mask com‐
69 binations can be encoded:
70 Subnet number Subnet mask Destination descriptor
72 0 0 0
73 10.0.0.0 255.0.0.0 8.10
74 10.0.0.0 255.255.255.0 24.10.0.0
75 10.17.0.0 255.255.0.0 16.10.17
76 10.27.129.0 255.255.255.0 24.10.27.129
77 10.229.0.128 255.255.255.128 25.10.229.0.128
78 10.198.122.47 255.255.255.255 32.10.198.122.47
79
81 Sometimes it's helpful to be able to set the value of a DHCP option
82 based on some value that the client has sent. To do this, you can use
83 expression evaluation. The dhcp-eval(5) manual page describes how to
84 write expressions. To assign the result of an evaluation to an option,
85 define the option as follows:
86 option my-option = expression ;
88 For example:
90 option hostname = binary-to-ascii (16, 8, "-",
92 substring (hardware, 1, 6));
93
95 Starting with 4.3.0 when ISC adds new option definitions those defini‐
96 tions will be included in the code based on the definition of an argu‐
97 ment for the RFC that defines the option in includes/site.h. This pro‐
98 vides you with a method for over-riding the ISC definitions if neces‐
99 sary - for example if you have previously defined the option with a
100 different format using the mechanism from DEFINING NEW OPTIONS below.
101 By default all of the options are enabled. In order to disable an
103 option you would edit the includes/site.h file and comment out the def‐
104 inition for the proper RFC.
105
107 The documentation for the various options mentioned below is taken from
108 the latest IETF draft document on DHCP options. Options not listed
109 below may not yet be implemented, but it is possible to use such
110 options by defining them in the configuration file. Please see the
111 DEFINING NEW OPTIONS heading later in this document for more informa‐
112 tion.
113 Some of the options documented here are automatically generated by the
115 DHCP server or by clients, and cannot be configured by the user. The
116 value of such an option can be used in the configuration file of the
117 receiving DHCP protocol agent (server or client), for example in condi‐
118 tional expressions. However, the value of the option cannot be used in
119 the configuration file of the sending agent, because the value is
120 determined only after the configuration file has been processed. In the
121 following documentation, such options will be shown as "not user con‐
122 figurable"
123 The standard options are:
125 option all-subnets-local flag;
127 This option specifies whether or not the client may assume that all
129 subnets of the IP network to which the client is connected use the
130 same MTU as the subnet of that network to which the client is
131 directly connected. A value of true indicates that all subnets share
132 the same MTU. A value of false means that the client should assume
133 that some subnets of the directly connected network may have smaller
134 MTUs.
135 option arp-cache-timeout uint32;
137 This option specifies the timeout in seconds for ARP cache entries.
139 option associated-ip ip-address [, ip-address... ];
141 This option is part of lease query. It is used to return all of the
143 IP addresses associated with a given DHCP client.
144 This option is not user configurable.
146 option bcms-controller-address ip-address [, ip-address... ];
148 This option configures a list of IPv4 addresses for use as Broadcast
150 and Multicast Controller Servers ("BCMS").
151 option bcms-controller-names domain-list;
153 This option contains the domain names of local Broadcast and Multi‐
155 cast Controller Servers ("BCMS") controllers which the client may
156 use.
157 option bootfile-name text;
159 This option is used to identify a bootstrap file. If supported by
161 the client, it should have the same effect as the filename declara‐
162 tion. BOOTP clients are unlikely to support this option. Some DHCP
163 clients will support it, and others actually require it.
164 option boot-size uint16;
166 This option specifies the length in 512-octet blocks of the default
168 boot image for the client.
169 option broadcast-address ip-address;
171 This option specifies the broadcast address in use on the client's
173 subnet. Legal values for broadcast addresses are specified in sec‐
174 tion 3.2.1.3 of STD 3 (RFC1122).
175 option capwap-ac-v4 ip-address [, ip-address ... ] ;
177 A list of IPv4 addresses of CAPWAP ACs that the WTP may use. The
179 addresses are listed in preference order.
180 This option is included based on RFC 5417.
182 option client-last-transaction-time uint32;
184 This option is part of lease query. It allows the receiver to deter‐
186 mine the time of the most recent access by the client. The value is
187 a duration in seconds from when the client last communicated with the
188 DHCP server.
189 This option is not user configurable.
191 option cookie-servers ip-address [, ip-address... ];
193 The cookie server option specifies a list of RFC 865 cookie servers
195 available to the client. Servers should be listed in order of pref‐
196 erence.
197 option default-ip-ttl uint8;
199 This option specifies the default time-to-live that the client should
201 use on outgoing datagrams.
202 option default-tcp-ttl uint8;
204 This option specifies the default TTL that the client should use when
206 sending TCP segments. The minimum value is 1.
207 option default-url string;
209 The format and meaning of this option is not described in any stan‐
211 dards document, but is claimed to be in use by Apple Computer. It is
212 not known what clients may reasonably do if supplied with this
213 option. Use at your own risk.
214 option dhcp-client-identifier string;
216 This option can be used to specify a DHCP client identifier in a host
218 declaration, so that dhcpd can find the host record by matching
219 against the client identifier.
220 Please be aware that some DHCP clients, when configured with client
222 identifiers that are ASCII text, will prepend a zero to the ASCII
223 text. So you may need to write:
224 option dhcp-client-identifier "\0foo";
226 rather than:
228 option dhcp-client-identifier "foo";
230 option dhcp-lease-time uint32;
232 This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
234 to allow the client to request a lease time for the IP address. In a
235 server reply (DHCPOFFER), a DHCP server uses this option to specify
236 the lease time it is willing to offer.
237 This option is not directly user configurable in the server; refer to
239 the max-lease-time and default-lease-time server options in
240 dhcpd.conf(5).
241 option dhcp-max-message-size uint16;
243 This option, when sent by the client, specifies the maximum size of
245 any response that the server sends to the client. When specified on
246 the server, if the client did not send a dhcp-max-message-size
247 option, the size specified on the server is used. This works for
248 BOOTP as well as DHCP responses.
249 option dhcp-message text;
251 This option is used by a DHCP server to provide an error message to a
253 DHCP client in a DHCPNAK message in the event of a failure. A client
254 may use this option in a DHCPDECLINE message to indicate why the
255 client declined the offered parameters.
256 This option is not user configurable.
258 option dhcp-message-type uint8;
260 This option, sent by both client and server, specifies the type of
262 DHCP message contained in the DHCP packet. Possible values (taken
263 directly from RFC2132) are:
264 1 DHCPDISCOVER
266 2 DHCPOFFER
267 3 DHCPREQUEST
268 4 DHCPDECLINE
269 5 DHCPACK
270 6 DHCPNAK
271 7 DHCPRELEASE
272 8 DHCPINFORM
273 This option is not user configurable.
275 option dhcp-option-overload uint8;
277 This option is used to indicate that the DHCP ´sname´ or ´file´
279 fields are being overloaded by using them to carry DHCP options. A
280 DHCP server inserts this option if the returned parameters will
281 exceed the usual space allotted for options.
282 If this option is present, the client interprets the specified addi‐
284 tional fields after it concludes interpretation of the standard
285 option fields.
286 Legal values for this option are:
288 1 the ´file´ field is used to hold options
290 2 the ´sname´ field is used to hold options
291 3 both fields are used to hold options
292 This option is not user configurable.
294 option dhcp-parameter-request-list uint8 [, uint8... ];
296 This option, when sent by the client, specifies which options the
298 client wishes the server to return. Normally, in the ISC DHCP
299 client, this is done using the request statement. If this option is
300 not specified by the client, the DHCP server will normally return
301 every option that is valid in scope and that fits into the reply.
302 When this option is specified on the server, the server returns the
303 specified options. This can be used to force a client to take
304 options that it hasn't requested, and it can also be used to tailor
305 the response of the DHCP server for clients that may need a more lim‐
306 ited set of options than those the server would normally return.
307 option dhcp-rebinding-time uint32;
309 This option specifies the number of seconds from the time a client
311 gets an address until the client transitions to the REBINDING state.
312 This option is user configurable, but it will be ignored if the value
314 is greater than or equal to the lease time.
315 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
317 figured in this option is also used as a DHCPv6 "T1" (renew) time.
318 option dhcp-renewal-time uint32;
320 This option specifies the number of seconds from the time a client
322 gets an address until the client transitions to the RENEWING state.
323 This option is user configurable, but it will be ignored if the value
325 is greater than or equal to the rebinding time, or lease time.
326 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
328 figured in this option is also used as a DHCPv6 "T2" (rebind) time.
329 option dhcp-requested-address ip-address;
331 This option is used by the client in a DHCPDISCOVER to request that a
333 particular IP address be assigned.
334 This option is not user configurable.
336 option dhcp-server-identifier ip-address;
338 This option is used in DHCPOFFER and DHCPREQUEST messages, and may
340 optionally be included in the DHCPACK and DHCPNAK messages. DHCP
341 servers include this option in the DHCPOFFER in order to allow the
342 client to distinguish between lease offers. DHCP clients use the
343 contents of the ´server identifier´ field as the destination address
344 for any DHCP messages unicast to the DHCP server. DHCP clients also
345 indicate which of several lease offers is being accepted by including
346 this option in a DHCPREQUEST message.
347 The value of this option is the IP address of the server.
349 This option is not directly user configurable. See the server-identi‐
351 fier server option in dhcpd.conf(5).
352 option domain-name text;
354 This option specifies the domain name that client should use when
356 resolving hostnames via the Domain Name System.
357 option domain-name-servers ip-address [, ip-address... ];
359 The domain-name-servers option specifies a list of Domain Name System
361 (STD 13, RFC 1035) name servers available to the client. Servers
362 should be listed in order of preference.
363 option domain-search domain-list;
365 The domain-search option specifies a ´search list´ of Domain Names to
367 be used by the client to locate not-fully-qualified domain names.
368 The difference between this option and historic use of the domain-
369 name option for the same ends is that this option is encoded in
370 RFC1035 compressed labels on the wire. For example:
371 option domain-search "example.com", "sales.example.com",
373 "eng.example.com";
374 option extensions-path text;
376 This option specifies the name of a file containing additional
378 options to be interpreted according to the DHCP option format as
379 specified in RFC2132.
380 option finger-server ip-address [, ip-address... ];
382 The Finger server option specifies a list of Finger servers available
384 to the client. Servers should be listed in order of preference.
385 option font-servers ip-address [, ip-address... ];
387 This option specifies a list of X Window System Font servers avail‐
389 able to the client. Servers should be listed in order of preference.
390 option geoconf-civic string;
392 A string to hold the geoconf civic structure.
394 This option is included based on RFC 4776.
396 option host-name string;
398 This option specifies the name of the client. The name may or may
400 not be qualified with the local domain name (it is preferable to use
401 the domain-name option to specify the domain name). See RFC 1035 for
402 character set restrictions. This option is only honored by dhclient-
403 script(8) if the hostname for the client machine is not set.
404 option ieee802-3-encapsulation flag;
406 This option specifies whether or not the client should use Ethernet
408 Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the
409 interface is an Ethernet. A value of false indicates that the client
410 should use RFC 894 encapsulation. A value of true means that the
411 client should use RFC 1042 encapsulation.
412 option ien116-name-servers ip-address [, ip-address... ];
414 The ien116-name-servers option specifies a list of IEN 116 name
416 servers available to the client. Servers should be listed in order
417 of preference.
418 option impress-servers ip-address [, ip-address... ];
420 The impress-server option specifies a list of Imagen Impress servers
422 available to the client. Servers should be listed in order of pref‐
423 erence.
424 option interface-mtu uint16;
426 This option specifies the MTU to use on this interface. The minimum
428 legal value for the MTU is 68.
429 option ip-forwarding flag;
431 This option specifies whether the client should configure its IP
433 layer for packet forwarding. A value of false means disable IP for‐
434 warding, and a value of true means enable IP forwarding.
435 option irc-server ip-address [, ip-address... ];
437 The IRC server option specifies a list of IRC servers available to
439 the client. Servers should be listed in order of preference.
440 option log-servers ip-address [, ip-address... ];
442 The log-server option specifies a list of MIT-LCS UDP log servers
444 available to the client. Servers should be listed in order of pref‐
445 erence.
446 option lpr-servers ip-address [, ip-address... ];
448 The LPR server option specifies a list of RFC 1179 line printer
450 servers available to the client. Servers should be listed in order
451 of preference.
452 option mask-supplier flag;
454 This option specifies whether or not the client should respond to
456 subnet mask requests using ICMP. A value of false indicates that the
457 client should not respond. A value of true means that the client
458 should respond.
459 option max-dgram-reassembly uint16;
461 This option specifies the maximum size datagram that the client
463 should be prepared to reassemble. The minimum legal value is 576.
464 option merit-dump text;
466 This option specifies the path-name of a file to which the client's
468 core image should be dumped in the event the client crashes. The
469 path is formatted as a character string consisting of characters from
470 the NVT ASCII character set.
471 option mobile-ip-home-agent ip-address [, ip-address... ];
473 This option specifies a list of IP addresses indicating mobile IP
475 home agents available to the client. Agents should be listed in
476 order of preference, although normally there will be only one such
477 agent.
478 option name-service-search uint16 [, uint6... ];
480 This option specifies a list of name services in the order the client
482 should attempt to use them.
483 This option is included based on RFC 2937.
485 option nds-context string;
487 The nds-context option specifies the name of the initial Netware
489 Directory Service for an NDS client.
490 option nds-servers ip-address [, ip-address... ];
492 The nds-servers option specifies a list of IP addresses of NDS
494 servers.
495 option nds-tree-name string;
497 The nds-tree-name option specifies NDS tree name that the NDS client
499 should use.
500 option netbios-dd-server ip-address [, ip-address... ];
502 The NetBIOS datagram distribution server (NBDD) option specifies a
504 list of RFC 1001/1002 NBDD servers listed in order of preference.
505 option netbios-name-servers ip-address [, ip-address...];
507 The NetBIOS name server (NBNS) option specifies a list of RFC
509 1001/1002 NBNS name servers listed in order of preference. NetBIOS
510 Name Service is currently more commonly referred to as WINS. WINS
511 servers can be specified using the netbios-name-servers option.
512 option netbios-node-type uint8;
514 The NetBIOS node type option allows NetBIOS over TCP/IP clients which
516 are configurable to be configured as described in RFC 1001/1002. The
517 value is specified as a single octet which identifies the client
518 type.
519 Possible node types are:
521 1 B-node: Broadcast - no WINS
523 2 P-node: Peer - WINS only
525 4 M-node: Mixed - broadcast, then WINS
527 8 H-node: Hybrid - WINS, then broadcast
529 option netbios-scope string;
531 The NetBIOS scope option specifies the NetBIOS over TCP/IP scope
533 parameter for the client as specified in RFC 1001/1002. See RFC1001,
534 RFC1002, and RFC1035 for character-set restrictions.
535 option netinfo-server-address ip-address [, ip-address... ];
537 The netinfo-server-address option has not been described in any RFC,
539 but has been allocated (and is claimed to be in use) by Apple Comput‐
540 ers. It's hard to say if the above is the correct format, or what
541 clients might be expected to do if values were configured. Use at
542 your own risk.
543 option netinfo-server-tag text;
545 The netinfo-server-tag option has not been described in any RFC, but
547 has been allocated (and is claimed to be in use) by Apple Computers.
548 It's hard to say if the above is the correct format, or what clients
549 might be expected to do if values were configured. Use at your own
550 risk.
551 option nis-domain text;
553 This option specifies the name of the client's NIS (Sun Network
555 Information Services) domain. The domain is formatted as a character
556 string consisting of characters from the NVT ASCII character set.
557 option nis-servers ip-address [, ip-address... ];
559 This option specifies a list of IP addresses indicating NIS servers
561 available to the client. Servers should be listed in order of pref‐
562 erence.
563 option nisplus-domain text;
565 This option specifies the name of the client's NIS+ domain. The
567 domain is formatted as a character string consisting of characters
568 from the NVT ASCII character set.
569 option nisplus-servers ip-address [, ip-address... ];
571 This option specifies a list of IP addresses indicating NIS+ servers
573 available to the client. Servers should be listed in order of pref‐
574 erence.
575 option nntp-server ip-address [, ip-address... ];
577 The NNTP server option specifies a list of NNTP servers available to
579 the client. Servers should be listed in order of preference.
580 option non-local-source-routing flag;
582 This option specifies whether the client should configure its IP
584 layer to allow forwarding of datagrams with non-local source routes
585 (see Section 3.3.5 of [4] for a discussion of this topic). A value
586 of false means disallow forwarding of such datagrams, and a value of
587 true means allow forwarding.
588 option ntp-servers ip-address [, ip-address... ];
590 This option specifies a list of IP addresses indicating NTP (RFC
592 5905) servers available to the client. Servers should be listed in
593 order of preference.
594 option nwip-domain string;
596 The name of the NetWare/IP domain that a NetWare/IP client should
598 use.
599 option nwip-suboptions string;
601 A sequence of suboptions for NetWare/IP clients - see RFC2242 for
603 details. Normally this option is set by specifying specific Net‐
604 Ware/IP suboptions - see the NETWARE/IP SUBOPTIONS section for more
605 information.
606 option option-6rd uint8 uint8 ip6-address ip-address [, ip-address
608 ...];
609 This option contains information about the rapid deployment option.
611 It is 8 bits of ipv4 mask length, 8 bits of 6rd prefix length, an
612 ipv6 prefix as an ipv6 address and a list of one or more ipv4
613 addresses.
614 This option is included based on RFC 5969.
616 option pana-agent ip-address [, ip-address ... ] ;
618 A set of IPv4 addresses of a PAA for the client to use. The
620 addresses are listed in preferred order.
621 This option is included based on RFC 5192.
623 option path-mtu-aging-timeout uint32;
625 This option specifies the timeout (in seconds) to use when aging Path
627 MTU values discovered by the mechanism defined in RFC 1191.
628 option path-mtu-plateau-table uint16 [, uint16... ];
630 This option specifies a table of MTU sizes to use when performing
632 Path MTU Discovery as defined in RFC 1191. The table is formatted as
633 a list of 16-bit unsigned integers, ordered from smallest to largest.
634 The minimum MTU value cannot be smaller than 68.
635 option pcode text;
637 This option specifies a string suitable for the TZ variable.
639 This option is included based on RFC 4833.
641 option perform-mask-discovery flag;
643 This option specifies whether or not the client should perform subnet
645 mask discovery using ICMP. A value of false indicates that the
646 client should not perform mask discovery. A value of true means that
647 the client should perform mask discovery.
648 option policy-filter ip-address ip-address
650 [, ip-address ip-address...];
651 This option specifies policy filters for non-local source routing.
653 The filters consist of a list of IP addresses and masks which specify
654 destination/mask pairs with which to filter incoming source routes.
655 Any source routed datagram whose next-hop address does not match one
657 of the filters should be discarded by the client.
658 See STD 3 (RFC1122) for further information.
660 option pop-server ip-address [, ip-address... ];
662 The POP3 server option specifies a list of POP3 servers available to
664 the client. Servers should be listed in order of preference.
665 option rdnss-selection uint8 ip-address ip-address domain-name;
667 The rdnss-selection option specifies an 8 bit flags field, a primary
669 and secondary ip address for the name server and a domainlist of
670 domains for which the RDNSS has special knowledge.
671 This option is included based on RFC 6731.
673 option resource-location-servers ip-address
675 [, ip-address...];
676 This option specifies a list of RFC 887 Resource Location servers
678 available to the client. Servers should be listed in order of pref‐
679 erence.
680 option root-path text;
682 This option specifies the path-name that contains the client's root
684 disk. The path is formatted as a character string consisting of
685 characters from the NVT ASCII character set.
686 option router-discovery flag;
688 This option specifies whether or not the client should solicit
690 routers using the Router Discovery mechanism defined in RFC 1256. A
691 value of false indicates that the client should not perform router
692 discovery. A value of true means that the client should perform
693 router discovery.
694 option router-solicitation-address ip-address;
696 This option specifies the address to which the client should transmit
698 router solicitation requests.
699 option routers ip-address [, ip-address... ];
701 The routers option specifies a list of IP addresses for routers on
703 the client's subnet. Routers should be listed in order of prefer‐
704 ence.
705 option slp-directory-agent boolean ip-address [, ip-address... ];
707 This option specifies two things: the IP addresses of one or more
709 Service Location Protocol Directory Agents, and whether the use of
710 these addresses is mandatory. If the initial boolean value is true,
711 the SLP agent should just use the IP addresses given. If the value
712 is false, the SLP agent may additionally do active or passive multi‐
713 cast discovery of SLP agents (see RFC2165 for details).
714 Please note that in this option and the slp-service-scope option, the
716 term "SLP Agent" is being used to refer to a Service Location Proto‐
717 col agent running on a machine that is being configured using the
718 DHCP protocol.
719 Also, please be aware that some companies may refer to SLP as NDS.
721 If you have an NDS directory agent whose address you need to config‐
722 ure, the slp-directory-agent option should work.
723 option slp-service-scope boolean text;
725 The Service Location Protocol Service Scope Option specifies two
727 things: a list of service scopes for SLP, and whether the use of this
728 list is mandatory. If the initial boolean value is true, the SLP
729 agent should only use the list of scopes provided in this option;
730 otherwise, it may use its own static configuration in preference to
731 the list provided in this option.
732 The text string should be a comma-separated list of scopes that the
734 SLP agent should use. It may be omitted, in which case the SLP Agent
735 will use the aggregated list of scopes of all directory agents known
736 to the SLP agent.
737 option smtp-server ip-address [, ip-address... ];
739 The SMTP server option specifies a list of SMTP servers available to
741 the client. Servers should be listed in order of preference.
742 option static-routes ip-address ip-address
744 [, ip-address ip-address...];
745 This option specifies a list of static routes that the client should
747 install in its routing cache. If multiple routes to the same desti‐
748 nation are specified, they are listed in descending order of prior‐
749 ity.
750 The routes consist of a list of IP address pairs. The first address
752 is the destination address, and the second address is the router for
753 the destination.
754 The default route (0.0.0.0) is an illegal destination for a static
756 route. To specify the default route, use the routers option. Also,
757 please note that this option is not intended for classless IP routing
758 - it does not include a subnet mask. Since classless IP routing is
759 now the most widely deployed routing standard, this option is virtu‐
760 ally useless, and is not implemented by any of the popular DHCP
761 clients, for example the Microsoft DHCP client.
762 NOTE to Fedora dhclient users:
764 dhclient-script interprets trailing 0 octets of the target as indi‐
765 cating the subnet class of the route, so for the following static-
766 routes value:
767 option static-routes 172.0.0.0 172.16.2.254,
768 192.168.0.0 192.168.2.254;
769 dhclient-script will create routes:
770 172/8 via 172.16.2.254 dev $interface
771 192.168/16 via 192.168.2.254 dev $interface
772 option classless-static-routes destination-descriptor ip-address
774 [, destination-descriptor ip-address...];
775 This option (see RFC3442) specifies a list of classless static routes
777 that the client should install in its routing cache.
778 This option can contain one or more static routes, each of which con‐
780 sists of a destination descriptor and the IP address of the router
781 that should be used to reach that destination.
782 Many clients may not implement the Classless Static Routes option.
784 DHCP server administrators should therefore configure their DHCP
785 servers to send both a Router option and a Classless Static Routes
786 option, and should specify the default router(s) both in the Router
787 option and in the Classless Static Routes option.
788 If the DHCP server returns both a Classless Static Routes option and
790 a Router option, the DHCP client ignores the Router option.
791 option streettalk-directory-assistance-server ip-address
793 [, ip-address...];
794 The StreetTalk Directory Assistance (STDA) server option specifies a
796 list of STDA servers available to the client. Servers should be
797 listed in order of preference.
798 option streettalk-server ip-address [, ip-address... ];
800 The StreetTalk server option specifies a list of StreetTalk servers
802 available to the client. Servers should be listed in order of pref‐
803 erence.
804 option subnet-mask ip-address;
806 The subnet mask option specifies the client's subnet mask as per RFC
808 950. If no subnet mask option is provided anywhere in scope, as a
809 last resort dhcpd will use the subnet mask from the subnet declara‐
810 tion for the network on which an address is being assigned. However,
811 any subnet-mask option declaration that is in scope for the address
812 being assigned will override the subnet mask specified in the subnet
813 declaration.
814 option subnet-selection ip-address;
816 Sent by the client if an address is required in a subnet other than
818 the one that would normally be selected (based on the relaying
819 address of the connected subnet the request is obtained from). See
820 RFC3011. Note that the option number used by this server is 118; this
821 has not always been the defined number, and some clients may use a
822 different value. Use of this option should be regarded as slightly
823 experimental!
824 This option is not user configurable in the server.
826 option swap-server ip-address;
828 This specifies the IP address of the client's swap server.
830 option tcp-keepalive-garbage flag;
832 This option specifies whether or not the client should send TCP
834 keepalive messages with an octet of garbage for compatibility with
835 older implementations. A value of false indicates that a garbage
836 octet should not be sent. A value of true indicates that a garbage
837 octet should be sent.
838 option tcp-keepalive-interval uint32;
840 This option specifies the interval (in seconds) that the client TCP
842 should wait before sending a keepalive message on a TCP connection.
843 The time is specified as a 32-bit unsigned integer. A value of zero
844 indicates that the client should not generate keepalive messages on
845 connections unless specifically requested by an application.
846 option tcode text;
848 This option specifies a name of a zone entry in the TZ database.
850 This option is included based on RFC 4833.
852 option tftp-server-name text;
854 This option is used to identify a TFTP server and, if supported by
856 the client, should have the same effect as the server-name declara‐
857 tion. BOOTP clients are unlikely to support this option. Some DHCP
858 clients will support it, and others actually require it.
859 option time-offset int32;
861 The time-offset option specifies the offset of the client's subnet in
863 seconds from Coordinated Universal Time (UTC).
864 option time-servers ip-address [, ip-address... ];
866 The time-server option specifies a list of RFC 868 time servers
868 available to the client. Servers should be listed in order of pref‐
869 erence.
870 option trailer-encapsulation flag;
872 This option specifies whether or not the client should negotiate the
874 use of trailers (RFC 893 [14]) when using the ARP protocol. A value
875 of false indicates that the client should not attempt to use trail‐
876 ers. A value of true means that the client should attempt to use
877 trailers.
878 option uap-servers text;
880 This option specifies a list of URLs, each pointing to a user authen‐
882 tication service that is capable of processing authentication
883 requests encapsulated in the User Authentication Protocol (UAP). UAP
884 servers can accept either HTTP 1.1 or SSLv3 connections. If the list
885 includes a URL that does not contain a port component, the normal
886 default port is assumed (i.e., port 80 for http and port 443 for
887 https). If the list includes a URL that does not contain a path com‐
888 ponent, the path /uap is assumed. If more than one URL is specified
889 in this list, the URLs are separated by spaces.
890 option user-class string;
892 This option is used by some DHCP clients as a way for users to spec‐
894 ify identifying information to the client. This can be used in a
895 similar way to the vendor-class-identifier option, but the value of
896 the option is specified by the user, not the vendor. Most recent
897 DHCP clients have a way in the user interface to specify the value
898 for this identifier, usually as a text string.
899 option v4-access-domain domain-name;
901 The domain name associated with the access network for use with LIS
903 Discovery.
904 This option is included based on RFC 5986.
906 option v4-lost domain-name;
908 The domain name of the LoST server for the client to use.
910 This option is included based on RFC 5223.
912 option vendor-class-identifier string;
914 This option is used by some DHCP clients to identify the vendor type
916 and possibly the configuration of a DHCP client. The information is
917 a string of bytes whose contents are specific to the vendor and are
918 not specified in a standard. To see what vendor class identifier
919 clients are sending, you can write the following in your DHCP server
920 configuration file:
921 set vendor-string = option vendor-class-identifier;
923 This will result in all entries in the DHCP server lease database
925 file for clients that sent vendor-class-identifier options having a
926 set statement that looks something like this:
927 set vendor-string = "SUNW.Ultra-5_10";
929 The vendor-class-identifier option is normally used by the DHCP
931 server to determine the options that are returned in the vendor-
932 encapsulated-options option. Please see the VENDOR ENCAPSULATED
933 OPTIONS section later in this manual page for further information.
934 option vendor-encapsulated-options string;
936 The vendor-encapsulated-options option can contain either a single
938 vendor-specific value or one or more vendor-specific suboptions.
939 This option is not normally specified in the DHCP server configura‐
940 tion file - instead, a vendor class is defined for each vendor, ven‐
941 dor class suboptions are defined, values for those suboptions are
942 defined, and the DHCP server makes up a response on that basis.
943 Some default behaviours for well-known DHCP client vendors (cur‐
945 rently, the Microsoft Windows 2000 DHCP client) are configured auto‐
946 matically, but otherwise this must be configured manually - see the
947 VENDOR ENCAPSULATED OPTIONS section later in this manual page for
948 details.
949 option vivso string;
951 The vivso option can contain multiple separate options, one for each
953 32-bit Enterprise ID. Each Enterprise-ID discriminated option then
954 contains additional options whose format is defined by the vendor who
955 holds that ID. This option is usually not configured manually, but
956 rather is configured via intervening option definitions. Please also
957 see the VENDOR ENCAPSULATED OPTIONS section later in this manual page
958 for details.
959 option www-server ip-address [, ip-address... ];
961 The WWW server option specifies a list of WWW servers available to
963 the client. Servers should be listed in order of preference.
964 option x-display-manager ip-address [, ip-address... ];
966 This option specifies a list of systems that are running the X Window
968 System Display Manager and are available to the client. Addresses
969 should be listed in order of preference.
970
972 An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
973 encapsulated options that a relay agent can add to a DHCP packet when
974 relaying it to the DHCP server. The server can then make address allo‐
975 cation decisions (or whatever other decisions it wants) based on these
976 options. The server also returns these options in any replies it sends
977 through the relay agent, so that the relay agent can use the informa‐
978 tion in these options for delivery or accounting purposes.
979 The current draft defines two options. To reference these options in
981 the dhcp server, specify the option space name, "agent", followed by a
982 period, followed by the option name. It is not normally useful to
983 define values for these options in the server, although it is permissi‐
984 ble. These options are not supported in the client.
985 option agent.circuit-id string;
987 The circuit-id suboption encodes an agent-local identifier of the
989 circuit from which a DHCP client-to-server packet was received. It
990 is intended for use by agents in relaying DHCP responses back to the
991 proper circuit. The format of this option is currently defined to be
992 vendor-dependent, and will probably remain that way, although the
993 current draft allows for the possibility of standardizing the format
994 in the future.
995 option agent.remote-id string;
997 The remote-id suboption encodes information about the remote host end
999 of a circuit. Examples of what it might contain include caller ID
1000 information, username information, remote ATM address, cable modem
1001 ID, and similar things. In principal, the meaning is not well-speci‐
1002 fied, and it should generally be assumed to be an opaque object that
1003 is administratively guaranteed to be unique to a particular remote
1004 end of a circuit.
1005 option agent.DOCSIS-device-class uint32;
1007 The DOCSIS-device-class suboption is intended to convey information
1009 about the host endpoint, hardware, and software, that either the host
1010 operating system or the DHCP server may not otherwise be aware of
1011 (but the relay is able to distinguish). This is implemented as a
1012 32-bit field (4 octets), each bit representing a flag describing the
1013 host in one of these ways. So far, only bit zero (being the least
1014 significant bit) is defined in RFC3256. If this bit is set to one,
1015 the host is considered a CPE Controlled Cable Modem (CCCM). All
1016 other bits are reserved.
1017 option agent.link-selection ip-address;
1019 The link-selection suboption is provided by relay agents to inform
1021 servers what subnet the client is actually attached to. This is use‐
1022 ful in those cases where the giaddr (where responses must be sent to
1023 the relay agent) is not on the same subnet as the client. When this
1024 option is present in a packet from a relay agent, the DHCP server
1025 will use its contents to find a subnet declared in configuration, and
1026 from here take one step further backwards to any shared-network the
1027 subnet may be defined within; the client may be given any address
1028 within that shared network, as normally appropriate.
1029
1031 The Client FQDN option, currently defined in the Internet Draft draft-
1032 ietf-dhc-fqdn-option-00.txt is not a standard yet, but is in suffi‐
1033 ciently wide use already that we have implemented it. Due to the com‐
1034 plexity of the option format, we have implemented it as a suboption
1035 space rather than a single option. In general this option should not
1036 be configured by the user - instead it should be used as part of an
1037 automatic DNS update system.
1038 option fqdn.no-client-update flag;
1040 When the client sends this, if it is true, it means the client will
1042 not attempt to update its A record. When sent by the server to the
1043 client, it means that the client should not update its own A record.
1044 option fqdn.server-update flag;
1046 When the client sends this to the server, it is requesting that the
1048 server update its A record. When sent by the server, it means that
1049 the server has updated (or is about to update) the client's A record.
1050 option fqdn.encoded flag;
1052 If true, this indicates that the domain name included in the option
1054 is encoded in DNS wire format, rather than as plain ASCII text. The
1055 client normally sets this to false if it doesn't support DNS wire
1056 format in the FQDN option. The server should always send back the
1057 same value that the client sent. When this value is set on the con‐
1058 figuration side, it controls the format in which the fqdn.fqdn subop‐
1059 tion is encoded.
1060 option fqdn.rcode1 flag;
1062 option fqdn.rcode2 flag;
1064 These options specify the result of the updates of the A and PTR
1066 records, respectively, and are only sent by the DHCP server to the
1067 DHCP client. The values of these fields are those defined in the DNS
1068 protocol specification.
1069 option fqdn.fqdn text;
1071 Specifies the domain name that the client wishes to use. This can be
1073 a fully-qualified domain name, or a single label. If there is no
1074 trailing ´.´ character in the name, it is not fully-qualified, and
1075 the server will generally update that name in some locally-defined
1076 domain.
1077 option fqdn.hostname --never set--;
1079 This option should never be set, but it can be read back using the
1081 option and config-option operators in an expression, in which case it
1082 returns the first label in the fqdn.fqdn suboption - for example, if
1083 the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will
1084 be "foo".
1085 option fqdn.domainname --never set--;
1087 This option should never be set, but it can be read back using the
1089 option and config-option operators in an expression, in which case it
1090 returns all labels after the first label in the fqdn.fqdn suboption -
1091 for example, if the value of fqdn.fqdn is "foo.example.com.", then
1092 fqdn.domainname will be "example.com.". If this suboption value is
1093 not set, it means that an unqualified name was sent in the fqdn
1094 option, or that no fqdn option was sent at all.
1095 If you wish to use any of these suboptions, we strongly recommend that
1097 you refer to the Client FQDN option draft (or standard, when it becomes
1098 a standard) - the documentation here is sketchy and incomplete in com‐
1099 parison, and is just intended for reference by people who already
1100 understand the Client FQDN option specification.
1101
1103 RFC2242 defines a set of encapsulated options for Novell NetWare/IP
1104 clients. To use these options in the dhcp server, specify the option
1105 space name, "nwip", followed by a period, followed by the option name.
1106 The following options can be specified:
1107 option nwip.nsq-broadcast flag;
1109 If true, the client should use the NetWare Nearest Server Query to
1111 locate a NetWare/IP server. The behaviour of the Novell client if
1112 this suboption is false, or is not present, is not specified.
1113 option nwip.preferred-dss ip-address [, ip-address... ];
1115 This suboption specifies a list of up to five IP addresses, each of
1117 which should be the IP address of a NetWare Domain SAP/RIP server
1118 (DSS).
1119 option nwip.nearest-nwip-server ip-address
1121 [, ip-address...];
1122 This suboption specifies a list of up to five IP addresses, each of
1124 which should be the IP address of a Nearest NetWare IP server.
1125 option nwip.autoretries uint8;
1127 Specifies the number of times that a NetWare/IP client should attempt
1129 to communicate with a given DSS server at startup.
1130 option nwip.autoretry-secs uint8;
1132 Specifies the number of seconds that a Netware/IP client should wait
1134 between retries when attempting to establish communications with a
1135 DSS server at startup.
1136 option nwip.nwip-1-1 uint8;
1138 If true, the NetWare/IP client should support NetWare/IP version 1.1
1140 compatibility. This is only needed if the client will be contacting
1141 Netware/IP version 1.1 servers.
1142 option nwip.primary-dss ip-address;
1144 Specifies the IP address of the Primary Domain SAP/RIP Service server
1146 (DSS) for this NetWare/IP domain. The NetWare/IP administration
1147 utility uses this value as Primary DSS server when configuring a sec‐
1148 ondary DSS server.
1149
1151 DHCPv6 options differ from DHCPv4 options partially due to using 16-bit
1152 code and length tags, but semantically zero-length options are legal in
1153 DHCPv6, and multiple options are treated differently. Whereas in
1154 DHCPv4 multiple options would be concatenated to form one option, in
1155 DHCPv6 they are expected to be individual instantiations. Understand‐
1156 ably, many options are not "allowed" to have multiple instances in a
1157 packet - normally these are options which are digested by the DHCP pro‐
1158 tocol software, and not by users or applications.
1159 option dhcp6.client-id string;
1161 This option specifies the client's DUID identifier. DUIDs are simi‐
1163 lar but different from DHCPv4 client identifiers - there are docu‐
1164 mented duid types:
1165 duid-llt
1167 duid-en
1169 duid-ll
1171 This value should not be configured, but rather is provided by
1173 clients and treated as an opaque identifier key blob by servers.
1174 option dhcp6.server-id string;
1176 This option specifies the server's DUID identifier. One may use this
1178 option to configure an opaque binary blob for your server's identi‐
1179 fier.
1180 option dhcp6.ia-na string;
1182 The Identity Association for Non-temporary Addresses (ia-na) carries
1184 assigned addresses that are not temporary addresses for use by the
1185 DHCPv6 client. This option is produced by the DHCPv6 server soft‐
1186 ware, and should not be configured.
1187 option dhcp6.ia-ta string;
1189 The Identity Association for Temporary Addresses (ia-ta) carries tem‐
1191 porary addresses, which may change upon every renewal. There is no
1192 support for this in the current DHCPv6 software.
1193 option dhcp6.ia-addr string;
1195 The Identity Association Address option is encapsulated inside ia-na
1197 or ia-ta options in order to represent addresses associated with
1198 those IA's. These options are manufactured by the software, so
1199 should not be configured.
1200 option dhcp6.oro uint16 [ , uint16, ... ];
1202 The Option Request Option ("ORO") is the DHCPv6 equivalent of the
1204 parameter-request-list. Clients supply this option to ask servers to
1205 reply with options relevant to their needs and use. This option must
1206 not be directly configured, the request syntax in dhclient.conf (5)
1207 should be used instead.
1208 option dhcp6.preference uint8;
1210 The preference option informs a DHCPv6 client which server is ´pre‐
1212 ferred´ for use on a given subnet. This preference is only applied
1213 during the initial stages of configuration - once a client is bound
1214 to an IA, it will remain bound to that IA until it is no longer valid
1215 or has expired. This value may be configured on the server, and is
1216 digested by the client software.
1217 option dhcp6.elapsed-time uint16;
1219 The elapsed-time option is constructed by the DHCPv6 client software,
1221 and is potentially consumed by intermediaries. This option should
1222 not be configured.
1223 option dhcp6.relay-msg string;
1225 The relay-msg option is constructed by intervening DHCPv6 relay agent
1227 software. This option is entirely used by protocol software, and is
1228 not meant for user configuration.
1229 option dhcp6.unicast ip6-address;
1231 The unicast option is provided by DHCPv6 servers which are willing
1233 (or prefer) to receive Request, Renew, Decline, and Release packets
1234 from their clients via unicast. Normally, DHCPv6 clients will multi‐
1235 cast these messages. Per RFC 3315, the server will reject a unicast
1236 message received from a client unless it previously sent (or would
1237 have sent) the unicast option to that client. This option may be
1238 configured on the server at the global and shared network level.
1239 When a unicast message is received, the server will check for an
1240 applicable definition of the unicast option. If such an option is
1241 found the message will be accepted, if not it will be rejected.
1242 option dhcp6.status-code status-code [ string ] ;
1244 The status-code option is provided by DHCPv6 servers to inform
1246 clients of error conditions during protocol communication. This
1247 option is manufactured and digested by protocol software, and should
1248 not be configured.
1249 option dhcp6.rapid-commit ;
1251 The rapid-commit option is a zero-length option that clients use to
1253 indicate their desire to enter into rapid-commit with the server.
1254 option dhcp6.vendor-opts string;
1256 The vendor-opts option is actually an encapsulated sub-option space,
1258 in which each Vendor-specific Information Option (VSIO) is identified
1259 by a 32-bit Enterprise-ID number. The encapsulated option spaces
1260 within these options are defined by the vendors.
1261 To make use of this option, the best way is to examine the section
1263 titled VENDOR ENCAPSULATED OPTIONS below, in particular the bits
1264 about the "vsio" option space.
1265 option dhcp6.interface-id string;
1267 The interface-id option is manufactured by relay agents, and may be
1269 used to guide configuration differentiating clients by the interface
1270 they are remotely attached to. It does not make sense to configure a
1271 value for this option, but it may make sense to inspect its contents.
1272 option dhcp6.reconf-msg dhcpv6-message;
1274 The reconf-msg option is manufactured by servers, and sent to clients
1276 in Reconfigure messages to inform them of what message the client
1277 should Reconfigure using. There is no support for DHCPv6 Reconfigure
1278 extensions, and this option is documented informationally only.
1279 option dhcp6.reconf-accept ;
1281 The reconf-accept option is included by DHCPv6 clients that support
1283 the Reconfigure extensions, advertising that they will respond if the
1284 server were to ask them to Reconfigure. There is no support for
1285 DHCPv6 Reconfigure extensions, and this option is documented informa‐
1286 tionally only.
1287 option dhcp6.sip-servers-names domain-list;
1289 The sip-servers-names option allows SIP clients to locate a local SIP
1291 server that is to be used for all outbound SIP requests, a so-
1292 called"outbound proxy server." If you wish to use manually entered
1293 IPv6 addresses instead, please see the sip-servers-addresses option
1294 below.
1295 option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;
1297 The sip-servers-addresses option allows SIP clients to locate a local
1299 SIP server that is to be used for all outbound SIP requests, a so-
1300 called "outbound proxy servers." If you wish to use domain names
1301 rather than IPv6 addresses, please see the sip-servers-names option
1302 above.
1303 option dhcp6.name-servers ip6-address [, ip6-address ... ] ;
1305 The name-servers option instructs clients about locally available
1307 recursive DNS servers. It is easiest to describe this as the "name‐
1308 server" line in /etc/resolv.conf.
1309 option dhcp6.domain-search domain-list;
1311 The domain-search option specifies the client's domain search path to
1313 be applied to recursive DNS queries. It is easiest to describe this
1314 as the "search" line in /etc/resolv.conf.
1315 option dhcp6.ia-pd string;
1317 The ia-pd option is manufactured by clients and servers to create a
1319 Prefix Delegation binding - to delegate an IPv6 prefix to the client.
1320 It is not directly edited in dhcpd.conf(5) or dhclient.conf(5), but
1321 rather is manufactured and consumed by the software.
1322 option dhcp6.ia-prefix string;
1324 The ia-prefix option is placed inside ia-pd options in order to iden‐
1326 tify the prefix(es) allocated to the client. It is not directly
1327 edited in dhcpd.conf(5) or dhclient.conf(5), but rather is manufac‐
1328 tured and consumed by the software.
1329 option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;
1331 The nis-servers option identifies, in order, NIS servers available to
1333 the client.
1334 option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;
1336 The nisp-servers option identifies, in order, NIS+ servers available
1338 to the client.
1339 option nis-domain-name domain-list;
1341 The nis-domain-name option specifies the NIS domain name the client
1343 is expected to use, and is related to the nis-servers option.
1344 option dhcp6.nis-domain-name domain-name;
1346 The dhcp6.nis-domain-name option specifies NIS domain name the client
1348 is expected to use, and is related to dhcp6.nis-servers option.
1349 option nisp-domain-name domain-list;
1351 The nisp-domain-name option specifies the NIS+ domain name the client
1353 is expected to use, and is related to the nisp-servers option.
1354 option dhcp6.nisp-domain-name domain-name;
1356 The dhcp6.nis-domain-name option specifies NIS+ domain name the
1358 client is expected to use, and is related to dhcp6.nisp-servers
1359 option.
1360 option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;
1362 The sntp-servers option specifies a list of local SNTP servers avail‐
1364 able for the client to synchronize their clocks.
1365 option dhcp6.info-refresh-time uint32;
1367 The info-refresh-time option gives DHCPv6 clients using Information-
1369 request messages a hint as to how long they should between refreshing
1370 the information they were given. Note that this option will only be
1371 delivered to the client, and be likely to affect the client's behav‐
1372 iour, if the client requested the option.
1373 option dhcp6.bcms-server-d domain-list;
1375 The bcms-server-d option contains the domain names of local BCMS
1377 (Broadcast and Multicast Control Services) controllers which the
1378 client may use.
1379 option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;
1381 The bcms-server-a option contains the IPv6 addresses of local BCMS
1383 (Broadcast and Multicast Control Services) controllers which the
1384 client may use.
1385 option dhcp6.geoconf-civic string;
1387 A string to hold the geoconf civic structure.
1389 This option is included based on RFC 4776.
1391 option dhcp6.remote-id string;
1393 The remote-id option is constructed by relay agents, to inform the
1395 server of details pertaining to what the relay knows about the client
1396 (such as what port it is attached to, and so forth). The contents of
1397 this option have some vendor-specific structure (similar to VSIO),
1398 but we have chosen to treat this option as an opaque field.
1399 option dhcp6.subscriber-id string;
1401 The subscriber-id option is an opaque field provided by the relay
1403 agent, which provides additional information about the subscriber in
1404 question. The exact contents of this option depend upon the vendor
1405 and/or the operator's configuration of the remote device, and as such
1406 is an opaque field.
1407 option dhcp6.fqdn string;
1409 The fqdn option is normally constructed by the client or server, and
1411 negotiates the client's Fully Qualified Domain Name, as well as which
1412 party is responsible for Dynamic DNS Updates. See the section on the
1413 Client FQDN SubOptions for full details (the DHCPv4 and DHCPv6 FQDN
1414 options use the same "fqdn." encapsulated space, so are in all ways
1415 identical).
1416 option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;
1418 A set of IPv6 addresses of a PAA for the client to use. The
1420 addresses are listed in preferred order.
1421 This option is included based on RFC 5192.
1423 option dhcp6.new-posix-timezone text;
1425 This option specifies a string suitable for the TZ variable.
1427 This option is included based on RFC 4833.
1429 option dhcp6.new-tzdb-timezone text;
1431 This option specifies a name of a zone entry in the TZ database.
1433 This option is included based on RFC 4833.
1435 option dhcp6.ero uint16 [, uint16 ... ] ;
1437 A list of the options requested by the relay agent.
1439 This option is included based on RFC 4994.
1441 option dhcp6.lq-query string;
1443 The lq-query option is used internally for lease query.
1445 option dhcp6.client-data string;
1447 The client-data option is used internally for lease query.
1449 option dhcp6.clt-time uint32;
1451 The clt-time option is used internally for lease query.
1453 option dhcp6.lq-relay-data ip6-address string;
1455 The lq-relay-data option is used internally for lease query.
1457 option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;
1459 The lq-client-link option is used internally for lease query.
1461 option dhcp6.v6-lost domain-name;
1463 The domain name of the LoST server for the client to use.
1465 This option is included based on RFC 5223.
1467 option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;
1469 A list of IPv6 addresses of CAPWAP ACs that the WTP may use. The
1471 addresses are listed in preference order.
1472 This option is included based on RFC 5417.
1474 option dhcp6.relay-id string;
1476 The DUID for the relay agent.
1478 This option is included based on RFC 5460.
1480 option dhcp6.v6-access-domain domain-name;
1482 The domain name associated with the access network for use with LIS
1484 Discovery.
1485 This option is included based on RFC5986.
1487 option dhcp6.sip-ua-cs-list domain-list;
1489 The list of domain names in the SIP User Agent Configuration Service
1491 Domains.
1492 This option is included based on RFC 6011.
1494 option dhcp6.bootfile-url text;
1496 The URL for a boot file.
1498 This option is included based on RFC 5970.
1500 option dhcp6.bootfile-param string;
1502 A string for the parameters to the bootfile. See RFC 5970 for more
1504 description of the layout of the parameters within the string.
1505 This option is included based on RFC 5970.
1507 option dhcp6.client-arch-type uint16 [, uint16 ... ] ;
1509 A list of one or more architecture types described as 16 bit values.
1511 This option is included based on RFC 5970.
1513 option dhcp6.nii uint8 uint8 uint8;
1515 The client network interface identitier option supplies information
1517 about a client's level of UNDI support. The values are, in order,
1518 the type, the major value and the minor value.
1519 This option is included based on RFC5970.
1521 option dhcp6.aftr-name domain-name;
1523 A domain name of the AFTR tunnel endpoint.
1525 This option is included based on RFC 6334.
1527 option dhcp6.erp-local-domain-name domain-name;
1529 A domain name for the ERP domain.
1531 This option is included based on RFC 6440.
1533 option dhcp6.rdnss-selection ip6-address uint8 domain-name;
1535 RDNSS information consists of an IPv6 address of RDNSS, an 8 bit
1537 flags field and a domain-list of domains for which the RDNSS has spe‐
1538 cial knowledge.
1539 This option is included based on RFC 6731.
1541 option dhcp6.client-linklayer-addr string;
1543 A client link-layer address. The first two bytes must be the type of
1545 the link-layer followed by the address itself.
1546 This option is included based on RFC 6939.
1548 option dhcp6.link-address ip6-address;
1550 An IPv6 address used by a relay agent to indicate to the server the
1552 link on which the client is located.
1553 This option is included based on RFC 6977.
1555 option dhcp6.solmax-rt uint32;
1557 A value to override the default for SOL_MAX_RT. This is a 32 bit
1559 value.
1560 This option is included based on RFC 7083.
1562 option dhcp6.inf-max-rt uint32;
1564 A value to override the default for INF_MAX_RT. This is a 32 bit
1566 value.
1567 This option is included based on RFC 7083.
1569
1571 v6relay (relay-number, option) This option allows access to an option
1572 that has been added to a packet by a relay agent. Relay-number value
1573 selects the relay to examine and option is the option to find. In
1574 DHCPv6 each relay encapsulates the entire previous message into an
1575 option, adds its own options (if any) and sends the result onwards.
1576 The RFC specifies a limit of 32 hops. A relay-number of 0 is a no-op
1577 and means don't look at the relays. 1 is the relay that is closest to
1578 the client, 2 would be the next in from the client and so on. Any
1579 value greater than the max number of hops is which is closest to the
1580 server independent of number. To use this option in a class statement
1581 you would have something like this:
1582 match if v6relay(1, option dhcp6.subscriber-id) = "client_1";
1584
1586 The Internet Systems Consortium DHCP client and server provide the
1587 capability to define new options. Each DHCP option has a name, a code,
1588 and a structure. The name is used by you to refer to the option. The
1589 code is a number, used by the DHCP server and client to refer to an
1590 option. The structure describes what the contents of an option looks
1591 like.
1592 To define a new option, you need to choose a name for it that is not in
1594 use for some other option - for example, you can't use "host-name"
1595 because the DHCP protocol already defines a host-name option, which is
1596 documented earlier in this manual page. If an option name doesn't
1597 appear in this manual page, you can use it, but it's probably a good
1598 idea to put some kind of unique string at the beginning so you can be
1599 sure that future options don't take your name. For example, you might
1600 define an option, "local-host-name", feeling some confidence that no
1601 official DHCP option name will ever start with "local".
1602 Once you have chosen a name, you must choose a code. All codes between
1604 224 and 254 are reserved as ´site-local´ DHCP options, so you can pick
1605 any one of these for your site (not for your product/application). In
1606 RFC3942, site-local space was moved from starting at 128 to starting at
1607 224. In practice, some vendors have interpreted the protocol rather
1608 loosely and have used option code values greater than 128 themselves.
1609 There's no real way to avoid this problem, and it was thought to be
1610 unlikely to cause too much trouble in practice. If you come across a
1611 vendor-documented option code in either the new or old site-local spa‐
1612 ces, please contact your vendor and inform them about rfc3942.
1613 The structure of an option is simply the format in which the option
1615 data appears. The ISC DHCP server currently supports a few simple
1616 types, like integers, booleans, strings and IP addresses, and it also
1617 supports the ability to define arrays of single types or arrays of
1618 fixed sequences of types.
1619 New options are declared as follows:
1621 option new-name code new-code = definition ;
1623 The values of new-name and new-code should be the name you have chosen
1625 for the new option and the code you have chosen. The definition should
1626 be the definition of the structure of the option.
1627 The following simple option type definitions are supported:
1629 BOOLEAN
1631 option new-name code new-code = boolean ;
1633 An option of type boolean is a flag with a value of either on or off
1635 (or true or false). So an example use of the boolean type would be:
1636 option use-zephyr code 180 = boolean;
1638 option use-zephyr on;
1639 INTEGER
1641 option new-name code new-code = sign integer width ;
1643 The sign token should either be blank, unsigned or signed. The width
1645 can be either 8, 16 or 32, and refers to the number of bits in the
1646 integer. So for example, the following two lines show a definition of
1647 the sql-connection-max option and its use:
1648 option sql-connection-max code 192 = unsigned integer 16;
1650 option sql-connection-max 1536;
1651 IP-ADDRESS
1653 option new-name code new-code = ip-address ;
1655 An option whose structure is an IP address can be expressed either as a
1657 domain name or as a dotted quad. So the following is an example use of
1658 the ip-address type:
1659 option sql-server-address code 193 = ip-address;
1661 option sql-server-address sql.example.com;
1662 IP6-ADDRESS
1664 option new-name code new-code = ip6-address ;
1666 An option whose structure is an IPv6 address must be expressed as a
1668 valid IPv6 address. The following is an example use of the ip6-address
1669 type:
1670 option dhcp6.some-server code 1234 = array of ip6-address;
1672 option dhcp6.some-server 3ffe:bbbb:aaaa:aaaa::1, 3ffe:bbbb:aaaa:aaaa::2;
1673 TEXT
1676 option new-name code new-code = text ;
1678 An option whose type is text will encode an ASCII text string. For
1680 example:
1681 option sql-default-connection-name code 194 = text;
1683 option sql-default-connection-name "PRODZA";
1684 DATA STRING
1687 option new-name code new-code = string ;
1689 An option whose type is a data string is essentially just a collection
1691 of bytes, and can be specified either as quoted text, like the text
1692 type, or as a list of hexadecimal contents separated by colons whose
1693 values must be between 0 and FF. For example:
1694 option sql-identification-token code 195 = string;
1696 option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;
1697 DOMAIN-LIST
1700 option new-name code new-code = domain-list [compressed] ;
1702 An option whose type is domain-list is an RFC1035 formatted (on the
1704 wire, "DNS Format") list of domain names, separated by root labels.
1705 The optional compressed keyword indicates if the option should be com‐
1706 pressed relative to the start of the option contents (not the packet
1707 contents).
1708 When in doubt, omit the compressed keyword. When the software receives
1710 an option that is compressed and the compressed keyword is omitted, it
1711 will still decompress the option (relative to the option contents
1712 field). The keyword only controls whether or not transmitted packets
1713 are compressed.
1714 Note that when domain-list formatted options are output as environment
1716 variables to dhclient-script(8), the standard DNS -escape mechanism is
1717 used: they are decimal. This is appropriate for direct use in eg
1718 /etc/resolv.conf.
1719 ENCAPSULATION
1722 option new-name code new-code = encapsulate identifier ;
1724 An option whose type is encapsulate will encapsulate the contents of
1726 the option space specified in identifier. Examples of encapsulated
1727 options in the DHCP protocol as it currently exists include the vendor-
1728 encapsulated-options option, the netware-suboptions option and the
1729 relay-agent-information option.
1730 option space local;
1732 option local.demo code 1 = text;
1733 option local-encapsulation code 197 = encapsulate local;
1734 option local.demo "demo";
1735 ARRAYS
1738 Options can contain arrays of any of the above types except for the
1740 text and data string types, which aren't currently supported in arrays.
1741 An example of an array definition is as follows:
1742 option kerberos-servers code 200 = array of ip-address;
1744 option kerberos-servers 10.20.10.1, 10.20.11.1;
1745 RECORDS
1747 Options can also contain data structures consisting of a sequence of
1749 data types, which is sometimes called a record type. For example:
1750 option contrived-001 code 201 = { boolean, integer 32, text };
1752 option contrived-001 on 1772 "contrivance";
1753 It's also possible to have options that are arrays of records, for
1755 example:
1756 option new-static-routes code 201 = array of {
1758 ip-address, ip-address, ip-address, integer 8 };
1759 option static-routes
1760 10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
1761 10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
1762 10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;
1763
1766 The DHCP protocol defines the vendor-encapsulated-options option, which
1767 allows vendors to define their own options that will be sent encapsu‐
1768 lated in a standard DHCP option. It also defines the Vendor Identified
1769 Vendor Sub Options option ("VIVSO"), and the DHCPv6 protocol defines
1770 the Vendor-specific Information Option ("VSIO"). The format of all of
1771 these options is usually internally a string of options, similarly to
1772 other normal DHCP options. The VIVSO and VSIO options differ in that
1773 they contain options that correspond to vendor Enterprise-ID numbers
1774 (assigned by IANA), which then contain options according to each Ven‐
1775 dor's specifications. You will need to refer to your vendor's documen‐
1776 tation in order to form options to their specification.
1777 The value of these options can be set in one of two ways. The first
1779 way is to simply specify the data directly, using a text string or a
1780 colon-separated list of hexadecimal values. For help in forming these
1781 strings, please refer to RFC2132 for the DHCPv4 Vendor Specific Infor‐
1782 mation Option, RFC3925 for the DHCPv4 Vendor Identified Vendor Sub
1783 Options, or RFC3315 for the DHCPv6 Vendor-specific Information Option.
1784 For example:
1785 option vendor-encapsulated-options
1787 2:4:
1788 AC:11:41:1:
1789 3:12:
1790 73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
1791 4:12:
1792 2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
1793 option vivso
1794 00:00:09:bf:0E:
1795 01:0c:
1796 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1797 option dhcp6.vendor-opts
1798 00:00:09:bf:
1799 00:01:00:0c:
1800 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1801 The second way of setting the value of these options is to have the
1803 DHCP server generate a vendor-specific option buffer. To do this, you
1804 must do four things: define an option space, define some options in
1805 that option space, provide values for them, and specify that that
1806 option space should be used to generate the relevant option.
1807 To define a new option space in which vendor options can be stored, use
1809 the option space statement:
1810 option space name [ [ code width number ] [ length width number ] [
1812 hash size number ] ] ;
1813 Where the numbers following code width, length width, and hash size
1815 respectively identify the number of bytes used to describe option
1816 codes, option lengths, and the size in buckets of the hash tables to
1817 hold options in this space (most DHCPv4 option spaces use 1 byte codes
1818 and lengths, which is the default, whereas most DHCPv6 option spaces
1819 use 2 byte codes and lengths).
1820 The code and length widths are used in DHCP protocol - you must config‐
1822 ure these numbers to match the applicable option space you are config‐
1823 uring. They each default to 1. Valid values for code widths are 1, 2
1824 or 4. Valid values for length widths are 0, 1 or 2. Most DHCPv4
1825 option spaces use 1 byte codes and lengths, which is the default,
1826 whereas most DHCPv6 option spaces use 2 byte codes and lengths. A
1827 zero-byte length produces options similar to the DHCPv6 Vendor-specific
1828 Information Option - but not their contents!
1829 The hash size defaults depend upon the code width selected, and may be
1831 254 or 1009. Valid values range between 1 and 65535. Note that the
1832 higher you configure this value, the more memory will be used. It is
1833 considered good practice to configure a value that is slightly larger
1834 than the estimated number of options you plan to configure within the
1835 space. Previous versions of ISC DHCP (up to and including DHCP 3.0.*),
1836 this value was fixed at 9973.
1837 The name can then be used in option definitions, as described earlier
1839 in this document. For example:
1840 option space SUNW code width 1 length width 1 hash size 3;
1842 option SUNW.server-address code 2 = ip-address;
1843 option SUNW.server-name code 3 = text;
1844 option SUNW.root-path code 4 = text;
1845 option space ISC code width 1 length width 1 hash size 3;
1847 option ISC.sample code 1 = text;
1848 option vendor.ISC code 2495 = encapsulate vivso-sample;
1849 option vendor-class.ISC code 2495 = text;
1850 option ISC.sample "configuration text here";
1852 option vendor-class.ISC "vendor class here";
1853 option space docsis code width 2 length width 2 hash size 17;
1855 option docsis.tftp-servers code 32 = array of ip6-address;
1856 option docsis.cablelabs-configuration-file code 33 = text;
1857 option docsis.cablelabs-syslog-servers code 34 = array of ip6-address;
1858 option docsis.device-id code 36 = string;
1859 option docsis.time-servers code 37 = array of ip6-address;
1860 option docsis.time-offset code 38 = signed integer 32;
1861 option vsio.docsis code 4491 = encapsulate docsis;
1862 Once you have defined an option space and the format of some options,
1864 you can set up scopes that define values for those options, and you can
1865 say when to use them. For example, suppose you want to handle two dif‐
1866 ferent classes of clients. Using the option space definition shown in
1867 the previous example, you can send different option values to different
1868 clients based on the vendor-class-identifier option that the clients
1869 send, as follows:
1870 class "vendor-classes" {
1872 match option vendor-class-identifier;
1873 }
1874 subclass "vendor-classes" "SUNW.Ultra-5_10" {
1876 vendor-option-space SUNW;
1877 option SUNW.root-path "/export/root/sparc";
1878 }
1879 subclass "vendor-classes" "SUNW.i86pc" {
1881 vendor-option-space SUNW;
1882 option SUNW.root-path "/export/root/i86pc";
1883 }
1884 option SUNW.server-address 172.17.65.1;
1886 option SUNW.server-name "sundhcp-server17-1";
1887 option vivso-sample.sample "Hello world!";
1889 option docsis.tftp-servers ::1;
1891 As you can see in the preceding example, regular scoping rules apply,
1894 so you can define values that are global in the global scope, and only
1895 define values that are specific to a particular class in the local
1896 scope. The vendor-option-space declaration tells the DHCP server to
1897 use options in the SUNW option space to construct the DHCPv4 vendor-
1898 encapsulated-options option. This is a limitation of that option - the
1899 DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi‐
1900 nitions all at once (even transmitted to the same client), so it is not
1901 necessary to configure this.
1902
1904 dhcpd.conf(5), dhcpd.leases(5), dhclient.conf(5), dhcp-eval(5),
1905 dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.
1906
1908 Information about Internet Systems Consortium can be found at
1909 https://www.isc.org.
1910 dhcp-options(5)