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 ad‐
26 dress (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. Additionally, please note the
29 software (dhcpd or dhclient) will only attempt to resolve the domain
30 name the first time the option is needed. For example, if the next-
31 server option is defined as a domain name, dhcpd will attempt to re‐
32 solve it while responding to the first client query dhcpd receives af‐
33 ter startup. Should the domain's address subsequently change, the soft‐
34 ware has to be restarted in order to pick up the change.
35 The ip6-address data specifies an IPv6 address, like ::1 or
37 3ffe:bbbb:aaaa:aaaa::1.
38 The int32 data type specifies a signed 32-bit integer. The uint32 data
40 type specifies an unsigned 32-bit integer. The int16 and uint16 data
41 types specify signed and unsigned 16-bit integers. The int8 and uint8
42 data types specify signed and unsigned 8-bit integers. Unsigned 8-bit
43 integers are also sometimes referred to as octets.
44 The text data type specifies an NVT ASCII string, which must be en‐
46 closed in double quotes - for example, to specify a root-path option,
47 the syntax would be
48 option root-path "10.0.1.4:/var/tmp/rootfs";
50 The domain-name data type specifies a domain name, which must not be
52 enclosed in double quotes. The domain name is stored just as if it
53 were a text option.
54 The domain-list data type specifies a list of domain names, enclosed in
56 double quotes and separated by commas ("example.com", "foo.exam‐
57 ple.com").
58 The flag data type specifies a boolean value. Booleans can be either
60 true or false (or on or off, if that makes more sense to you).
61 The string data type specifies either an NVT ASCII string enclosed in
63 double quotes, or a series of octets specified in hexadecimal, sepa‐
64 rated by colons. For example:
65 option dhcp-client-identifier "CLIENT-FOO";
67 or
68 option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f;
69 The destination-descriptor describe the IP subnet number and subnet
71 mask of a particular destination using a compact encoding. This encod‐
72 ing consists of one octet describing the width of the subnet mask, fol‐
73 lowed by all the significant octets of the subnet number. The follow‐
74 ing table contains some examples of how various subnet number/mask com‐
75 binations can be encoded:
76 Subnet number Subnet mask Destination descriptor
78 0 0 0
79 10.0.0.0 255.0.0.0 8.10
80 10.0.0.0 255.255.255.0 24.10.0.0
81 10.17.0.0 255.255.0.0 16.10.17
82 10.27.129.0 255.255.255.0 24.10.27.129
83 10.229.0.128 255.255.255.128 25.10.229.0.128
84 10.198.122.47 255.255.255.255 32.10.198.122.47
85
87 Sometimes it's helpful to be able to set the value of a DHCP option
88 based on some value that the client has sent. To do this, you can use
89 expression evaluation. The dhcp-eval(5) manual page describes how to
90 write expressions. To assign the result of an evaluation to an option,
91 define the option as follows:
92 option my-option = expression ;
94 For example:
96 option hostname = binary-to-ascii (16, 8, "-",
98 substring (hardware, 1, 6));
99
101 Starting with 4.3.0 when ISC adds new option definitions those defini‐
102 tions will be included in the code based on the definition of an argu‐
103 ment for the RFC that defines the option in includes/site.h. This pro‐
104 vides you with a method for over-riding the ISC definitions if neces‐
105 sary - for example if you have previously defined the option with a
106 different format using the mechanism from DEFINING NEW OPTIONS below.
107 By default all of the options are enabled. In order to disable an op‐
109 tion you would edit the includes/site.h file and comment out the defi‐
110 nition for the proper RFC.
111
113 The documentation for the various options mentioned below is taken from
114 the latest IETF draft document on DHCP options. Options not listed be‐
115 low may not yet be implemented, but it is possible to use such options
116 by defining them in the configuration file. Please see the DEFINING
117 NEW OPTIONS heading later in this document for more information.
118 Some of the options documented here are automatically generated by the
120 DHCP server or by clients, and cannot be configured by the user. The
121 value of such an option can be used in the configuration file of the
122 receiving DHCP protocol agent (server or client), for example in condi‐
123 tional expressions. However, the value of the option cannot be used in
124 the configuration file of the sending agent, because the value is de‐
125 termined only after the configuration file has been processed. In the
126 following documentation, such options will be shown as "not user con‐
127 figurable"
128 The standard options are:
130 option all-subnets-local flag;
132 This option specifies whether or not the client may assume that all
134 subnets of the IP network to which the client is connected use the
135 same MTU as the subnet of that network to which the client is di‐
136 rectly connected. A value of true indicates that all subnets share
137 the same MTU. A value of false means that the client should assume
138 that some subnets of the directly connected network may have smaller
139 MTUs.
140 option arp-cache-timeout uint32;
142 This option specifies the timeout in seconds for ARP cache entries.
144 option associated-ip ip-address [, ip-address... ];
146 This option is part of lease query. It is used to return all of the
148 IP addresses associated with a given DHCP client.
149 This option is not user configurable.
151 option bcms-controller-address ip-address [, ip-address... ];
153 This option configures a list of IPv4 addresses for use as Broadcast
155 and Multicast Controller Servers ("BCMS").
156 option bcms-controller-names domain-list;
158 This option contains the domain names of local Broadcast and Multi‐
160 cast Controller Servers ("BCMS") controllers which the client may
161 use.
162 option bootfile-name text;
164 This option is used to identify a bootstrap file. If supported by
166 the client, it should have the same effect as the filename declara‐
167 tion. BOOTP clients are unlikely to support this option. Some DHCP
168 clients will support it, and others actually require it.
169 option boot-size uint16;
171 This option specifies the length in 512-octet blocks of the default
173 boot image for the client.
174 option broadcast-address ip-address;
176 This option specifies the broadcast address in use on the client's
178 subnet. Legal values for broadcast addresses are specified in sec‐
179 tion 3.2.1.3 of STD 3 (RFC1122).
180 option capwap-ac-v4 ip-address [, ip-address ... ] ;
182 A list of IPv4 addresses of CAPWAP ACs that the WTP may use. The ad‐
184 dresses are listed in preference order.
185 This option is included based on RFC 5417.
187 option client-last-transaction-time uint32;
189 This option is part of lease query. It allows the receiver to deter‐
191 mine the time of the most recent access by the client. The value is
192 a duration in seconds from when the client last communicated with the
193 DHCP server.
194 This option is not user configurable.
196 option cookie-servers ip-address [, ip-address... ];
198 The cookie server option specifies a list of RFC 865 cookie servers
200 available to the client. Servers should be listed in order of pref‐
201 erence.
202 option default-ip-ttl uint8;
204 This option specifies the default time-to-live that the client should
206 use on outgoing datagrams.
207 option default-tcp-ttl uint8;
209 This option specifies the default TTL that the client should use when
211 sending TCP segments. The minimum value is 1.
212 option default-url string;
214 The format and meaning of this option is not described in any stan‐
216 dards document, but is claimed to be in use by Apple Computer. It is
217 not known what clients may reasonably do if supplied with this op‐
218 tion. Use at your own risk.
219 option dhcp-client-identifier string;
221 This option can be used to specify a DHCP client identifier in a host
223 declaration, so that dhcpd can find the host record by matching
224 against the client identifier.
225 Please be aware that some DHCP clients, when configured with client
227 identifiers that are ASCII text, will prepend a zero to the ASCII
228 text. So you may need to write:
229 option dhcp-client-identifier "\0foo";
231 rather than:
233 option dhcp-client-identifier "foo";
235 option dhcp-lease-time uint32;
237 This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
239 to allow the client to request a lease time for the IP address. In a
240 server reply (DHCPOFFER), a DHCP server uses this option to specify
241 the lease time it is willing to offer.
242 This option is not directly user configurable in the server; refer to
244 the max-lease-time and default-lease-time server options in
245 dhcpd.conf(5).
246 option dhcp-max-message-size uint16;
248 This option, when sent by the client, specifies the maximum size of
250 any response that the server sends to the client. When specified on
251 the server, if the client did not send a dhcp-max-message-size op‐
252 tion, the size specified on the server is used. This works for BOOTP
253 as well as DHCP responses.
254 option dhcp-message text;
256 This option is used by a DHCP server to provide an error message to a
258 DHCP client in a DHCPNAK message in the event of a failure. A client
259 may use this option in a DHCPDECLINE message to indicate why the
260 client declined the offered parameters.
261 This option is not user configurable.
263 option dhcp-message-type uint8;
265 This option, sent by both client and server, specifies the type of
267 DHCP message contained in the DHCP packet. Possible values (taken di‐
268 rectly from RFC2132) are:
269 1 DHCPDISCOVER
271 2 DHCPOFFER
272 3 DHCPREQUEST
273 4 DHCPDECLINE
274 5 DHCPACK
275 6 DHCPNAK
276 7 DHCPRELEASE
277 8 DHCPINFORM
278 This option is not user configurable.
280 option dhcp-option-overload uint8;
282 This option is used to indicate that the DHCP ´sname´ or ´file´
284 fields are being overloaded by using them to carry DHCP options. A
285 DHCP server inserts this option if the returned parameters will ex‐
286 ceed the usual space allotted for options.
287 If this option is present, the client interprets the specified addi‐
289 tional fields after it concludes interpretation of the standard op‐
290 tion fields.
291 Legal values for this option are:
293 1 the ´file´ field is used to hold options
295 2 the ´sname´ field is used to hold options
296 3 both fields are used to hold options
297 This option is not user configurable.
299 option dhcp-parameter-request-list uint8 [, uint8... ];
301 This option, when sent by the client, specifies which options the
303 client wishes the server to return. Normally, in the ISC DHCP
304 client, this is done using the request statement. If this option is
305 not specified by the client, the DHCP server will normally return ev‐
306 ery option that is valid in scope and that fits into the reply. When
307 this option is specified on the server, the server returns the speci‐
308 fied options. This can be used to force a client to take options
309 that it hasn't requested, and it can also be used to tailor the re‐
310 sponse of the DHCP server for clients that may need a more limited
311 set of options than those the server would normally return.
312 option dhcp-rebinding-time uint32;
314 This option specifies the number of seconds from the time a client
316 gets an address until the client transitions to the REBINDING state.
317 This option is user configurable, but it will be ignored if the value
319 is greater than or equal to the lease time.
320 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
322 figured in this option is also used as a DHCPv6 "T1" (renew) time.
323 option dhcp-renewal-time uint32;
325 This option specifies the number of seconds from the time a client
327 gets an address until the client transitions to the RENEWING state.
328 This option is user configurable, but it will be ignored if the value
330 is greater than or equal to the rebinding time, or lease time.
331 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
333 figured in this option is also used as a DHCPv6 "T2" (rebind) time.
334 option dhcp-requested-address ip-address;
336 This option is used by the client in a DHCPDISCOVER to request that a
338 particular IP address be assigned.
339 This option is not user configurable.
341 option dhcp-server-identifier ip-address;
343 This option is used in DHCPOFFER and DHCPREQUEST messages, and may
345 optionally be included in the DHCPACK and DHCPNAK messages. DHCP
346 servers include this option in the DHCPOFFER in order to allow the
347 client to distinguish between lease offers. DHCP clients use the
348 contents of the ´server identifier´ field as the destination address
349 for any DHCP messages unicast to the DHCP server. DHCP clients also
350 indicate which of several lease offers is being accepted by including
351 this option in a DHCPREQUEST message.
352 The value of this option is the IP address of the server.
354 This option is not directly user configurable. See the server-identi‐
356 fier server option in dhcpd.conf(5).
357 option domain-name text;
359 This option specifies the domain name that client should use when re‐
361 solving hostnames via the Domain Name System.
362 option domain-name-servers ip-address [, ip-address... ];
364 The domain-name-servers option specifies a list of Domain Name System
366 (STD 13, RFC 1035) name servers available to the client. Servers
367 should be listed in order of preference.
368 option domain-search domain-list;
370 The domain-search option specifies a ´search list´ of Domain Names to
372 be used by the client to locate not-fully-qualified domain names.
373 The difference between this option and historic use of the domain-
374 name option for the same ends is that this option is encoded in
375 RFC1035 compressed labels on the wire. For example:
376 option domain-search "example.com", "sales.example.com",
378 "eng.example.com";
379 option extensions-path text;
381 This option specifies the name of a file containing additional op‐
383 tions to be interpreted according to the DHCP option format as speci‐
384 fied in RFC2132.
385 option finger-server ip-address [, ip-address... ];
387 The Finger server option specifies a list of Finger servers available
389 to the client. Servers should be listed in order of preference.
390 option font-servers ip-address [, ip-address... ];
392 This option specifies a list of X Window System Font servers avail‐
394 able to the client. Servers should be listed in order of preference.
395 option geoconf-civic string;
397 A string to hold the geoconf civic structure.
399 This option is included based on RFC 4776.
401 option host-name string;
403 This option specifies the name of the client. The name may or may
405 not be qualified with the local domain name (it is preferable to use
406 the domain-name option to specify the domain name). See RFC 1035 for
407 character set restrictions. This option is only honored by dhclient-
408 script(8) if the hostname for the client machine is not set.
409 option ieee802-3-encapsulation flag;
411 This option specifies whether or not the client should use Ethernet
413 Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the in‐
414 terface is an Ethernet. A value of false indicates that the client
415 should use RFC 894 encapsulation. A value of true means that the
416 client should use RFC 1042 encapsulation.
417 option ien116-name-servers ip-address [, ip-address... ];
419 The ien116-name-servers option specifies a list of IEN 116 name
421 servers available to the client. Servers should be listed in order
422 of preference.
423 option impress-servers ip-address [, ip-address... ];
425 The impress-server option specifies a list of Imagen Impress servers
427 available to the client. Servers should be listed in order of pref‐
428 erence.
429 option interface-mtu uint16;
431 This option specifies the MTU to use on this interface. The minimum
433 legal value for the MTU is 68.
434 option ip-forwarding flag;
436 This option specifies whether the client should configure its IP
438 layer for packet forwarding. A value of false means disable IP for‐
439 warding, and a value of true means enable IP forwarding.
440 option irc-server ip-address [, ip-address... ];
442 The IRC server option specifies a list of IRC servers available to
444 the client. Servers should be listed in order of preference.
445 option loader-configfile text
448 This option is used to specify a boot loading configuration file a
450 PXE client should use.
451 This option is included based on RFC 5071.
453 option loader-pathprefix text
455 This option is used to specify a path prefix a PXE client should use
457 in conjunction with the boot load configuration file.
458 This option is included based on RFC 5071.
460 option loader-reboottime uint32
462 This option is used to dictate the maximum amount of time a PXE
464 client should allow itself to achieve configured network resources
465 before rebooting.
466 This option is included based on RFC 5071.
468 option log-servers ip-address [, ip-address... ];
470 The log-server option specifies a list of MIT-LCS UDP log servers
472 available to the client. Servers should be listed in order of pref‐
473 erence.
474 option lpr-servers ip-address [, ip-address... ];
476 The LPR server option specifies a list of RFC 1179 line printer
478 servers available to the client. Servers should be listed in order
479 of preference.
480 option mask-supplier flag;
482 This option specifies whether or not the client should respond to
484 subnet mask requests using ICMP. A value of false indicates that the
485 client should not respond. A value of true means that the client
486 should respond.
487 option max-dgram-reassembly uint16;
489 This option specifies the maximum size datagram that the client
491 should be prepared to reassemble. The minimum legal value is 576.
492 option merit-dump text;
494 This option specifies the path-name of a file to which the client's
496 core image should be dumped in the event the client crashes. The
497 path is formatted as a character string consisting of characters from
498 the NVT ASCII character set.
499 option mobile-ip-home-agent ip-address [, ip-address... ];
501 This option specifies a list of IP addresses indicating mobile IP
503 home agents available to the client. Agents should be listed in or‐
504 der of preference, although normally there will be only one such
505 agent.
506 option name-service-search uint16 [, uint6... ];
508 This option specifies a list of name services in the order the client
510 should attempt to use them.
511 This option is included based on RFC 2937.
513 option nds-context string;
515 The nds-context option specifies the name of the initial Netware Di‐
517 rectory Service for an NDS client.
518 option nds-servers ip-address [, ip-address... ];
520 The nds-servers option specifies a list of IP addresses of NDS
522 servers.
523 option nds-tree-name string;
525 The nds-tree-name option specifies NDS tree name that the NDS client
527 should use.
528 option netbios-dd-server ip-address [, ip-address... ];
530 The NetBIOS datagram distribution server (NBDD) option specifies a
532 list of RFC 1001/1002 NBDD servers listed in order of preference.
533 option netbios-name-servers ip-address [, ip-address...];
535 The NetBIOS name server (NBNS) option specifies a list of RFC
537 1001/1002 NBNS name servers listed in order of preference. NetBIOS
538 Name Service is currently more commonly referred to as WINS. WINS
539 servers can be specified using the netbios-name-servers option.
540 option netbios-node-type uint8;
542 The NetBIOS node type option allows NetBIOS over TCP/IP clients which
544 are configurable to be configured as described in RFC 1001/1002. The
545 value is specified as a single octet which identifies the client
546 type.
547 Possible node types are:
549 1 B-node: Broadcast - no WINS
551 2 P-node: Peer - WINS only
553 4 M-node: Mixed - broadcast, then WINS
555 8 H-node: Hybrid - WINS, then broadcast
557 option netbios-scope string;
559 The NetBIOS scope option specifies the NetBIOS over TCP/IP scope pa‐
561 rameter for the client as specified in RFC 1001/1002. See RFC1001,
562 RFC1002, and RFC1035 for character-set restrictions.
563 option netinfo-server-address ip-address [, ip-address... ];
565 The netinfo-server-address option has not been described in any RFC,
567 but has been allocated (and is claimed to be in use) by Apple Comput‐
568 ers. It's hard to say if the above is the correct format, or what
569 clients might be expected to do if values were configured. Use at
570 your own risk.
571 option netinfo-server-tag text;
573 The netinfo-server-tag option has not been described in any RFC, but
575 has been allocated (and is claimed to be in use) by Apple Computers.
576 It's hard to say if the above is the correct format, or what clients
577 might be expected to do if values were configured. Use at your own
578 risk.
579 option nis-domain text;
581 This option specifies the name of the client's NIS (Sun Network In‐
583 formation Services) domain. The domain is formatted as a character
584 string consisting of characters from the NVT ASCII character set.
585 option nis-servers ip-address [, ip-address... ];
587 This option specifies a list of IP addresses indicating NIS servers
589 available to the client. Servers should be listed in order of pref‐
590 erence.
591 option nisplus-domain text;
593 This option specifies the name of the client's NIS+ domain. The do‐
595 main is formatted as a character string consisting of characters from
596 the NVT ASCII character set.
597 option nisplus-servers ip-address [, ip-address... ];
599 This option specifies a list of IP addresses indicating NIS+ servers
601 available to the client. Servers should be listed in order of pref‐
602 erence.
603 option nntp-server ip-address [, ip-address... ];
605 The NNTP server option specifies a list of NNTP servers available to
607 the client. Servers should be listed in order of preference.
608 option non-local-source-routing flag;
610 This option specifies whether the client should configure its IP
612 layer to allow forwarding of datagrams with non-local source routes
613 (see Section 3.3.5 of [4] for a discussion of this topic). A value
614 of false means disallow forwarding of such datagrams, and a value of
615 true means allow forwarding.
616 option ntp-servers ip-address [, ip-address... ];
618 This option specifies a list of IP addresses indicating NTP (RFC
620 5905) servers available to the client. Servers should be listed in
621 order of preference.
622 option nwip-domain string;
624 The name of the NetWare/IP domain that a NetWare/IP client should
626 use.
627 option nwip-suboptions string;
629 A sequence of suboptions for NetWare/IP clients - see RFC2242 for de‐
631 tails. Normally this option is set by specifying specific NetWare/IP
632 suboptions - see the NETWARE/IP SUBOPTIONS section for more informa‐
633 tion.
634 option pxe-system-type uint16 [, uint16 ... ];
636 A list of one ore more 16-bit integers which allows a client to spec‐
638 ify its pre-boot architecture type(s).
639 This option is included based on RFC 4578.
641 option pxe-interface-id uint8 uint8 uint8
643 A three octet value which allows a client to specify its network in‐
645 terface type.
646 This option is included based on RFC 4578.
648 option pxe-client-id uint8 string
650 A single octet indicating type, followed by a string that allows a
652 client to specify its PXE client identity.
653 This option is included based on RFC 4578.
655 option option-6rd uint8 uint8 ip6-address ip-address [, ip-address
657 ...];
658 This option contains information about the rapid deployment option.
660 It is 8 bits of ipv4 mask length, 8 bits of 6rd prefix length, an
661 ipv6 prefix as an ipv6 address and a list of one or more ipv4 ad‐
662 dresses.
663 This option is included based on RFC 5969.
665 option pana-agent ip-address [, ip-address ... ] ;
667 A set of IPv4 addresses of a PAA for the client to use. The ad‐
669 dresses are listed in preferred order.
670 This option is included based on RFC 5192.
672 option path-mtu-aging-timeout uint32;
674 This option specifies the timeout (in seconds) to use when aging Path
676 MTU values discovered by the mechanism defined in RFC 1191.
677 option path-mtu-plateau-table uint16 [, uint16... ];
679 This option specifies a table of MTU sizes to use when performing
681 Path MTU Discovery as defined in RFC 1191. The table is formatted as
682 a list of 16-bit unsigned integers, ordered from smallest to largest.
683 The minimum MTU value cannot be smaller than 68.
684 option pcode text;
686 This option specifies a string suitable for the TZ variable.
688 This option is included based on RFC 4833.
690 option perform-mask-discovery flag;
692 This option specifies whether or not the client should perform subnet
694 mask discovery using ICMP. A value of false indicates that the
695 client should not perform mask discovery. A value of true means that
696 the client should perform mask discovery.
697 option policy-filter ip-address ip-address
699 [, ip-address ip-address...];
700 This option specifies policy filters for non-local source routing.
702 The filters consist of a list of IP addresses and masks which specify
703 destination/mask pairs with which to filter incoming source routes.
704 Any source routed datagram whose next-hop address does not match one
706 of the filters should be discarded by the client.
707 See STD 3 (RFC1122) for further information.
709 option pop-server ip-address [, ip-address... ];
711 The POP3 server option specifies a list of POP3 servers available to
713 the client. Servers should be listed in order of preference.
714 option rdnss-selection uint8 ip-address ip-address domain-name;
716 The rdnss-selection option specifies an 8 bit flags field, a primary
718 and secondary ip address for the name server and a domainlist of do‐
719 mains for which the RDNSS has special knowledge.
720 This option is included based on RFC 6731.
722 option resource-location-servers ip-address
724 [, ip-address...];
725 This option specifies a list of RFC 887 Resource Location servers
727 available to the client. Servers should be listed in order of pref‐
728 erence.
729 option root-path text;
731 This option specifies the path-name that contains the client's root
733 disk. The path is formatted as a character string consisting of
734 characters from the NVT ASCII character set.
735 option router-discovery flag;
737 This option specifies whether or not the client should solicit
739 routers using the Router Discovery mechanism defined in RFC 1256. A
740 value of false indicates that the client should not perform router
741 discovery. A value of true means that the client should perform
742 router discovery.
743 option router-solicitation-address ip-address;
745 This option specifies the address to which the client should transmit
747 router solicitation requests.
748 option routers ip-address [, ip-address... ];
750 The routers option specifies a list of IP addresses for routers on
752 the client's subnet. Routers should be listed in order of prefer‐
753 ence.
754 option slp-directory-agent boolean ip-address [, ip-address... ];
756 This option specifies two things: the IP addresses of one or more
758 Service Location Protocol Directory Agents, and whether the use of
759 these addresses is mandatory. If the initial boolean value is true,
760 the SLP agent should just use the IP addresses given. If the value
761 is false, the SLP agent may additionally do active or passive multi‐
762 cast discovery of SLP agents (see RFC2165 for details).
763 Please note that in this option and the slp-service-scope option, the
765 term "SLP Agent" is being used to refer to a Service Location Proto‐
766 col agent running on a machine that is being configured using the
767 DHCP protocol.
768 Also, please be aware that some companies may refer to SLP as NDS.
770 If you have an NDS directory agent whose address you need to config‐
771 ure, the slp-directory-agent option should work.
772 option slp-service-scope boolean text;
774 The Service Location Protocol Service Scope Option specifies two
776 things: a list of service scopes for SLP, and whether the use of this
777 list is mandatory. If the initial boolean value is true, the SLP
778 agent should only use the list of scopes provided in this option;
779 otherwise, it may use its own static configuration in preference to
780 the list provided in this option.
781 The text string should be a comma-separated list of scopes that the
783 SLP agent should use. It may be omitted, in which case the SLP Agent
784 will use the aggregated list of scopes of all directory agents known
785 to the SLP agent.
786 option smtp-server ip-address [, ip-address... ];
788 The SMTP server option specifies a list of SMTP servers available to
790 the client. Servers should be listed in order of preference.
791 option static-routes ip-address ip-address
793 [, ip-address ip-address...];
794 This option specifies a list of static routes that the client should
796 install in its routing cache. If multiple routes to the same desti‐
797 nation are specified, they are listed in descending order of prior‐
798 ity.
799 The routes consist of a list of IP address pairs. The first address
801 is the destination address, and the second address is the router for
802 the destination.
803 The default route (0.0.0.0) is an illegal destination for a static
805 route. To specify the default route, use the routers option. Also,
806 please note that this option is not intended for classless IP routing
807 - it does not include a subnet mask. Since classless IP routing is
808 now the most widely deployed routing standard, this option is virtu‐
809 ally useless, and is not implemented by any of the popular DHCP
810 clients, for example the Microsoft DHCP client.
811 NOTE to Fedora dhclient users:
813 dhclient-script interprets trailing 0 octets of the target as indi‐
814 cating the subnet class of the route, so for the following static-
815 routes value:
816 option static-routes 172.0.0.0 172.16.2.254,
817 192.168.0.0 192.168.2.254;
818 dhclient-script will create routes:
819 172/8 via 172.16.2.254 dev $interface
820 192.168/16 via 192.168.2.254 dev $interface
821 option classless-static-routes destination-descriptor ip-address
823 [, destination-descriptor ip-address...];
824 This option (see RFC3442) specifies a list of classless static routes
826 that the client should install in its routing cache.
827 This option can contain one or more static routes, each of which con‐
829 sists of a destination descriptor and the IP address of the router
830 that should be used to reach that destination.
831 Many clients may not implement the Classless Static Routes option.
833 DHCP server administrators should therefore configure their DHCP
834 servers to send both a Router option and a Classless Static Routes
835 option, and should specify the default router(s) both in the Router
836 option and in the Classless Static Routes option.
837 If the DHCP server returns both a Classless Static Routes option and
839 a Router option, the DHCP client ignores the Router option.
840 option streettalk-directory-assistance-server ip-address
842 [, ip-address...];
843 The StreetTalk Directory Assistance (STDA) server option specifies a
845 list of STDA servers available to the client. Servers should be
846 listed in order of preference.
847 option streettalk-server ip-address [, ip-address... ];
849 The StreetTalk server option specifies a list of StreetTalk servers
851 available to the client. Servers should be listed in order of pref‐
852 erence.
853 option subnet-mask ip-address;
855 The subnet mask option specifies the client's subnet mask as per RFC
857 950. If no subnet mask option is provided anywhere in scope, as a
858 last resort dhcpd will use the subnet mask from the subnet declara‐
859 tion for the network on which an address is being assigned. However,
860 any subnet-mask option declaration that is in scope for the address
861 being assigned will override the subnet mask specified in the subnet
862 declaration.
863 option subnet-selection ip-address;
865 Sent by the client if an address is required in a subnet other than
867 the one that would normally be selected (based on the relaying ad‐
868 dress of the connected subnet the request is obtained from). See
869 RFC3011. Note that the option number used by this server is 118; this
870 has not always been the defined number, and some clients may use a
871 different value. Use of this option should be regarded as slightly
872 experimental!
873 This option is not user configurable in the server.
875 option swap-server ip-address;
877 This specifies the IP address of the client's swap server.
879 option tftp-server-address ip-address [, ip-address... ];
881 This option configures a list of one or more IPv4 addresses of tftp
883 servers a client may use.
884 This option is included based on RFC 5859
886 option tcp-keepalive-garbage flag;
888 This option specifies whether or not the client should send TCP
890 keepalive messages with an octet of garbage for compatibility with
891 older implementations. A value of false indicates that a garbage
892 octet should not be sent. A value of true indicates that a garbage
893 octet should be sent.
894 option tcp-keepalive-interval uint32;
896 This option specifies the interval (in seconds) that the client TCP
898 should wait before sending a keepalive message on a TCP connection.
899 The time is specified as a 32-bit unsigned integer. A value of zero
900 indicates that the client should not generate keepalive messages on
901 connections unless specifically requested by an application.
902 option tcode text;
904 This option specifies a name of a zone entry in the TZ database.
906 This option is included based on RFC 4833.
908 option tftp-server-name text;
910 This option is used to identify a TFTP server and, if supported by
912 the client, should have the same effect as the server-name declara‐
913 tion. BOOTP clients are unlikely to support this option. Some DHCP
914 clients will support it, and others actually require it.
915 option time-offset int32;
917 The time-offset option specifies the offset of the client's subnet in
919 seconds from Coordinated Universal Time (UTC).
920 option time-servers ip-address [, ip-address... ];
922 The time-server option specifies a list of RFC 868 time servers
924 available to the client. Servers should be listed in order of pref‐
925 erence.
926 option trailer-encapsulation flag;
928 This option specifies whether or not the client should negotiate the
930 use of trailers (RFC 893 [14]) when using the ARP protocol. A value
931 of false indicates that the client should not attempt to use trail‐
932 ers. A value of true means that the client should attempt to use
933 trailers.
934 option uap-servers text;
936 This option specifies a list of URLs, each pointing to a user authen‐
938 tication service that is capable of processing authentication re‐
939 quests encapsulated in the User Authentication Protocol (UAP). UAP
940 servers can accept either HTTP 1.1 or SSLv3 connections. If the list
941 includes a URL that does not contain a port component, the normal de‐
942 fault port is assumed (i.e., port 80 for http and port 443 for
943 https). If the list includes a URL that does not contain a path com‐
944 ponent, the path /uap is assumed. If more than one URL is specified
945 in this list, the URLs are separated by spaces.
946 option user-class string;
948 This option is used by some DHCP clients as a way for users to spec‐
950 ify identifying information to the client. This can be used in a
951 similar way to the vendor-class-identifier option, but the value of
952 the option is specified by the user, not the vendor. Most recent
953 DHCP clients have a way in the user interface to specify the value
954 for this identifier, usually as a text string.
955 option v4-access-domain domain-name;
957 The domain name associated with the access network for use with LIS
959 Discovery.
960 This option is included based on RFC 5986.
962 option v4-lost domain-name;
964 The domain name of the LoST server for the client to use.
966 This option is included based on RFC 5223.
968 option v6-only-preferred uint32;
970 The number of seconds the client should disable DHCPv4 for.
972 This option and its use by the client are specified in RFC 8925.
974 option vendor-class-identifier string;
976 This option is used by some DHCP clients to identify the vendor type
978 and possibly the configuration of a DHCP client. The information is
979 a string of bytes whose contents are specific to the vendor and are
980 not specified in a standard. To see what vendor class identifier
981 clients are sending, you can write the following in your DHCP server
982 configuration file:
983 set vendor-string = option vendor-class-identifier;
985 This will result in all entries in the DHCP server lease database
987 file for clients that sent vendor-class-identifier options having a
988 set statement that looks something like this:
989 set vendor-string = "SUNW.Ultra-5_10";
991 The vendor-class-identifier option is normally used by the DHCP
993 server to determine the options that are returned in the vendor-en‐
994 capsulated-options option. Please see the VENDOR ENCAPSULATED OP‐
995 TIONS section later in this manual page for further information.
996 option vendor-encapsulated-options string;
998 The vendor-encapsulated-options option can contain either a single
1000 vendor-specific value or one or more vendor-specific suboptions.
1001 This option is not normally specified in the DHCP server configura‐
1002 tion file - instead, a vendor class is defined for each vendor, ven‐
1003 dor class suboptions are defined, values for those suboptions are de‐
1004 fined, and the DHCP server makes up a response on that basis.
1005 Some default behaviours for well-known DHCP client vendors (cur‐
1007 rently, the Microsoft Windows 2000 DHCP client) are configured auto‐
1008 matically, but otherwise this must be configured manually - see the
1009 VENDOR ENCAPSULATED OPTIONS section later in this manual page for de‐
1010 tails.
1011 option vivso string;
1013 The vivso option can contain multiple separate options, one for each
1015 32-bit Enterprise ID. Each Enterprise-ID discriminated option then
1016 contains additional options whose format is defined by the vendor who
1017 holds that ID. This option is usually not configured manually, but
1018 rather is configured via intervening option definitions. Please also
1019 see the VENDOR ENCAPSULATED OPTIONS section later in this manual page
1020 for details.
1021 option www-server ip-address [, ip-address... ];
1023 The WWW server option specifies a list of WWW servers available to
1025 the client. Servers should be listed in order of preference.
1026 option x-display-manager ip-address [, ip-address... ];
1028 This option specifies a list of systems that are running the X Window
1030 System Display Manager and are available to the client. Addresses
1031 should be listed in order of preference.
1032
1034 An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
1035 encapsulated options that a relay agent can add to a DHCP packet when
1036 relaying it to the DHCP server. The server can then make address allo‐
1037 cation decisions (or whatever other decisions it wants) based on these
1038 options. The server also returns these options in any replies it sends
1039 through the relay agent, so that the relay agent can use the informa‐
1040 tion in these options for delivery or accounting purposes.
1041 The current draft defines two options. To reference these options in
1043 the dhcp server, specify the option space name, "agent", followed by a
1044 period, followed by the option name. It is not normally useful to de‐
1045 fine values for these options in the server, although it is permissi‐
1046 ble. These options are not supported in the client.
1047 option agent.circuit-id string;
1049 The circuit-id suboption encodes an agent-local identifier of the
1051 circuit from which a DHCP client-to-server packet was received. It
1052 is intended for use by agents in relaying DHCP responses back to the
1053 proper circuit. The format of this option is currently defined to be
1054 vendor-dependent, and will probably remain that way, although the
1055 current draft allows for the possibility of standardizing the format
1056 in the future.
1057 option agent.remote-id string;
1059 The remote-id suboption encodes information about the remote host end
1061 of a circuit. Examples of what it might contain include caller ID
1062 information, username information, remote ATM address, cable modem
1063 ID, and similar things. In principal, the meaning is not well-speci‐
1064 fied, and it should generally be assumed to be an opaque object that
1065 is administratively guaranteed to be unique to a particular remote
1066 end of a circuit.
1067 option agent.DOCSIS-device-class uint32;
1069 The DOCSIS-device-class suboption is intended to convey information
1071 about the host endpoint, hardware, and software, that either the host
1072 operating system or the DHCP server may not otherwise be aware of
1073 (but the relay is able to distinguish). This is implemented as a
1074 32-bit field (4 octets), each bit representing a flag describing the
1075 host in one of these ways. So far, only bit zero (being the least
1076 significant bit) is defined in RFC3256. If this bit is set to one,
1077 the host is considered a CPE Controlled Cable Modem (CCCM). All
1078 other bits are reserved.
1079 option agent.link-selection ip-address;
1081 The link-selection suboption is provided by relay agents to inform
1083 servers what subnet the client is actually attached to. This is use‐
1084 ful in those cases where the giaddr (where responses must be sent to
1085 the relay agent) is not on the same subnet as the client. When this
1086 option is present in a packet from a relay agent, the DHCP server
1087 will use its contents to find a subnet declared in configuration, and
1088 from here take one step further backwards to any shared-network the
1089 subnet may be defined within; the client may be given any address
1090 within that shared network, as normally appropriate.
1091
1093 The Client FQDN option, currently defined in the Internet Draft draft-
1094 ietf-dhc-fqdn-option-00.txt is not a standard yet, but is in suffi‐
1095 ciently wide use already that we have implemented it. Due to the com‐
1096 plexity of the option format, we have implemented it as a suboption
1097 space rather than a single option. In general this option should not
1098 be configured by the user - instead it should be used as part of an au‐
1099 tomatic DNS update system.
1100 option fqdn.no-client-update flag;
1102 When the client sends this, if it is true, it means the client will
1104 not attempt to update its A record. When sent by the server to the
1105 client, it means that the client should not update its own A record.
1106 option fqdn.server-update flag;
1108 When the client sends this to the server, it is requesting that the
1110 server update its A record. When sent by the server, it means that
1111 the server has updated (or is about to update) the client's A record.
1112 option fqdn.encoded flag;
1114 If true, this indicates that the domain name included in the option
1116 is encoded in DNS wire format, rather than as plain ASCII text. The
1117 client normally sets this to false if it doesn't support DNS wire
1118 format in the FQDN option. The server should always send back the
1119 same value that the client sent. When this value is set on the con‐
1120 figuration side, it controls the format in which the fqdn.fqdn subop‐
1121 tion is encoded.
1122 option fqdn.rcode1 flag;
1124 option fqdn.rcode2 flag;
1126 These options specify the result of the updates of the A and PTR
1128 records, respectively, and are only sent by the DHCP server to the
1129 DHCP client. The values of these fields are those defined in the DNS
1130 protocol specification.
1131 option fqdn.fqdn text;
1133 Specifies the domain name that the client wishes to use. This can be
1135 a fully-qualified domain name, or a single label. If there is no
1136 trailing ´.´ character in the name, it is not fully-qualified, and
1137 the server will generally update that name in some locally-defined
1138 domain.
1139 option fqdn.hostname --never set--;
1141 This option should never be set, but it can be read back using the
1143 option and config-option operators in an expression, in which case it
1144 returns the first label in the fqdn.fqdn suboption - for example, if
1145 the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will
1146 be "foo".
1147 option fqdn.domainname --never set--;
1149 This option should never be set, but it can be read back using the
1151 option and config-option operators in an expression, in which case it
1152 returns all labels after the first label in the fqdn.fqdn suboption -
1153 for example, if the value of fqdn.fqdn is "foo.example.com.", then
1154 fqdn.domainname will be "example.com.". If this suboption value is
1155 not set, it means that an unqualified name was sent in the fqdn op‐
1156 tion, or that no fqdn option was sent at all.
1157 If you wish to use any of these suboptions, we strongly recommend that
1159 you refer to the Client FQDN option draft (or standard, when it becomes
1160 a standard) - the documentation here is sketchy and incomplete in com‐
1161 parison, and is just intended for reference by people who already un‐
1162 derstand the Client FQDN option specification.
1163
1165 RFC2242 defines a set of encapsulated options for Novell NetWare/IP
1166 clients. To use these options in the dhcp server, specify the option
1167 space name, "nwip", followed by a period, followed by the option name.
1168 The following options can be specified:
1169 option nwip.nsq-broadcast flag;
1171 If true, the client should use the NetWare Nearest Server Query to
1173 locate a NetWare/IP server. The behaviour of the Novell client if
1174 this suboption is false, or is not present, is not specified.
1175 option nwip.preferred-dss ip-address [, ip-address... ];
1177 This suboption specifies a list of up to five IP addresses, each of
1179 which should be the IP address of a NetWare Domain SAP/RIP server
1180 (DSS).
1181 option nwip.nearest-nwip-server ip-address
1183 [, ip-address...];
1184 This suboption specifies a list of up to five IP addresses, each of
1186 which should be the IP address of a Nearest NetWare IP server.
1187 option nwip.autoretries uint8;
1189 Specifies the number of times that a NetWare/IP client should attempt
1191 to communicate with a given DSS server at startup.
1192 option nwip.autoretry-secs uint8;
1194 Specifies the number of seconds that a Netware/IP client should wait
1196 between retries when attempting to establish communications with a
1197 DSS server at startup.
1198 option nwip.nwip-1-1 uint8;
1200 If true, the NetWare/IP client should support NetWare/IP version 1.1
1202 compatibility. This is only needed if the client will be contacting
1203 Netware/IP version 1.1 servers.
1204 option nwip.primary-dss ip-address;
1206 Specifies the IP address of the Primary Domain SAP/RIP Service server
1208 (DSS) for this NetWare/IP domain. The NetWare/IP administration
1209 utility uses this value as Primary DSS server when configuring a sec‐
1210 ondary DSS server.
1211
1213 DHCPv6 options differ from DHCPv4 options partially due to using 16-bit
1214 code and length tags, but semantically zero-length options are legal in
1215 DHCPv6, and multiple options are treated differently. Whereas in
1216 DHCPv4 multiple options would be concatenated to form one option, in
1217 DHCPv6 they are expected to be individual instantiations. Understand‐
1218 ably, many options are not "allowed" to have multiple instances in a
1219 packet - normally these are options which are digested by the DHCP pro‐
1220 tocol software, and not by users or applications.
1221 option dhcp6.client-id string;
1223 This option specifies the client's DUID identifier. DUIDs are simi‐
1225 lar but different from DHCPv4 client identifiers - there are docu‐
1226 mented duid types:
1227 duid-llt
1229 duid-en
1231 duid-ll
1233 This value should not be configured, but rather is provided by
1235 clients and treated as an opaque identifier key blob by servers.
1236 option dhcp6.server-id string;
1238 This option specifies the server's DUID identifier. One may use this
1240 option to configure an opaque binary blob for your server's identi‐
1241 fier.
1242 option dhcp6.ia-na string;
1244 The Identity Association for Non-temporary Addresses (ia-na) carries
1246 assigned addresses that are not temporary addresses for use by the
1247 DHCPv6 client. This option is produced by the DHCPv6 server soft‐
1248 ware, and should not be configured.
1249 option dhcp6.ia-ta string;
1251 The Identity Association for Temporary Addresses (ia-ta) carries tem‐
1253 porary addresses, which may change upon every renewal. There is no
1254 support for this in the current DHCPv6 software.
1255 option dhcp6.ia-addr string;
1257 The Identity Association Address option is encapsulated inside ia-na
1259 or ia-ta options in order to represent addresses associated with
1260 those IA's. These options are manufactured by the software, so
1261 should not be configured.
1262 option dhcp6.oro uint16 [ , uint16, ... ];
1264 The Option Request Option ("ORO") is the DHCPv6 equivalent of the pa‐
1266 rameter-request-list. Clients supply this option to ask servers to
1267 reply with options relevant to their needs and use. This option must
1268 not be directly configured, the request syntax in dhclient.conf (5)
1269 should be used instead.
1270 option dhcp6.preference uint8;
1272 The preference option informs a DHCPv6 client which server is ´pre‐
1274 ferred´ for use on a given subnet. This preference is only applied
1275 during the initial stages of configuration - once a client is bound
1276 to an IA, it will remain bound to that IA until it is no longer valid
1277 or has expired. This value may be configured on the server, and is
1278 digested by the client software.
1279 option dhcp6.elapsed-time uint16;
1281 The elapsed-time option is constructed by the DHCPv6 client software,
1283 and is potentially consumed by intermediaries. This option should
1284 not be configured.
1285 option dhcp6.relay-msg string;
1287 The relay-msg option is constructed by intervening DHCPv6 relay agent
1289 software. This option is entirely used by protocol software, and is
1290 not meant for user configuration.
1291 option dhcp6.unicast ip6-address;
1293 The unicast option is provided by DHCPv6 servers which are willing
1295 (or prefer) to receive Request, Renew, Decline, and Release packets
1296 from their clients via unicast. Normally, DHCPv6 clients will multi‐
1297 cast these messages. Per RFC 3315, the server will reject a unicast
1298 message received from a client unless it previously sent (or would
1299 have sent) the unicast option to that client. This option may be
1300 configured on the server at the global and shared network level.
1301 When a unicast message is received, the server will check for an ap‐
1302 plicable definition of the unicast option. If such an option is
1303 found the message will be accepted, if not it will be rejected.
1304 option dhcp6.status-code status-code [ string ] ;
1306 The status-code option is provided by DHCPv6 servers to inform
1308 clients of error conditions during protocol communication. This op‐
1309 tion is manufactured and digested by protocol software, and should
1310 not be configured.
1311 option dhcp6.rapid-commit ;
1313 The rapid-commit option is a zero-length option that clients use to
1315 indicate their desire to enter into rapid-commit with the server.
1316 option dhcp6.vendor-opts string;
1318 The vendor-opts option is actually an encapsulated sub-option space,
1320 in which each Vendor-specific Information Option (VSIO) is identified
1321 by a 32-bit Enterprise-ID number. The encapsulated option spaces
1322 within these options are defined by the vendors.
1323 To make use of this option, the best way is to examine the section
1325 titled VENDOR ENCAPSULATED OPTIONS below, in particular the bits
1326 about the "vsio" option space.
1327 option dhcp6.interface-id string;
1329 The interface-id option is manufactured by relay agents, and may be
1331 used to guide configuration differentiating clients by the interface
1332 they are remotely attached to. It does not make sense to configure a
1333 value for this option, but it may make sense to inspect its contents.
1334 option dhcp6.reconf-msg dhcpv6-message;
1336 The reconf-msg option is manufactured by servers, and sent to clients
1338 in Reconfigure messages to inform them of what message the client
1339 should Reconfigure using. There is no support for DHCPv6 Reconfigure
1340 extensions, and this option is documented informationally only.
1341 option dhcp6.reconf-accept ;
1343 The reconf-accept option is included by DHCPv6 clients that support
1345 the Reconfigure extensions, advertising that they will respond if the
1346 server were to ask them to Reconfigure. There is no support for
1347 DHCPv6 Reconfigure extensions, and this option is documented informa‐
1348 tionally only.
1349 option dhcp6.sip-servers-names domain-list;
1351 The sip-servers-names option allows SIP clients to locate a local SIP
1353 server that is to be used for all outbound SIP requests, a so-
1354 called"outbound proxy server." If you wish to use manually entered
1355 IPv6 addresses instead, please see the sip-servers-addresses option
1356 below.
1357 option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;
1359 The sip-servers-addresses option allows SIP clients to locate a local
1361 SIP server that is to be used for all outbound SIP requests, a so-
1362 called "outbound proxy servers." If you wish to use domain names
1363 rather than IPv6 addresses, please see the sip-servers-names option
1364 above.
1365 option dhcp6.name-servers ip6-address [, ip6-address ... ] ;
1367 The name-servers option instructs clients about locally available re‐
1369 cursive DNS servers. It is easiest to describe this as the "name‐
1370 server" line in /etc/resolv.conf.
1371 option dhcp6.domain-search domain-list;
1373 The domain-search option specifies the client's domain search path to
1375 be applied to recursive DNS queries. It is easiest to describe this
1376 as the "search" line in /etc/resolv.conf.
1377 option dhcp6.ia-pd string;
1379 The ia-pd option is manufactured by clients and servers to create a
1381 Prefix Delegation binding - to delegate an IPv6 prefix to the client.
1382 It is not directly edited in dhcpd.conf(5) or dhclient.conf(5), but
1383 rather is manufactured and consumed by the software.
1384 option dhcp6.ia-prefix string;
1386 The ia-prefix option is placed inside ia-pd options in order to iden‐
1388 tify the prefix(es) allocated to the client. It is not directly
1389 edited in dhcpd.conf(5) or dhclient.conf(5), but rather is manufac‐
1390 tured and consumed by the software.
1391 option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;
1393 The nis-servers option identifies, in order, NIS servers available to
1395 the client.
1396 option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;
1398 The nisp-servers option identifies, in order, NIS+ servers available
1400 to the client.
1401 option nis-domain-name domain-list;
1403 The nis-domain-name option specifies the NIS domain name the client
1405 is expected to use, and is related to the nis-servers option.
1406 option dhcp6.nis-domain-name domain-name;
1408 The dhcp6.nis-domain-name option specifies NIS domain name the client
1410 is expected to use, and is related to dhcp6.nis-servers option.
1411 option nisp-domain-name domain-list;
1413 The nisp-domain-name option specifies the NIS+ domain name the client
1415 is expected to use, and is related to the nisp-servers option.
1416 option dhcp6.nisp-domain-name domain-name;
1418 The dhcp6.nis-domain-name option specifies NIS+ domain name the
1420 client is expected to use, and is related to dhcp6.nisp-servers op‐
1421 tion.
1422 option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;
1424 The sntp-servers option specifies a list of local SNTP servers avail‐
1426 able for the client to synchronize their clocks.
1427 option dhcp6.info-refresh-time uint32;
1429 The info-refresh-time option gives DHCPv6 clients using Information-
1431 request messages a hint as to how long they should between refreshing
1432 the information they were given. Note that this option will only be
1433 delivered to the client, and be likely to affect the client's behav‐
1434 iour, if the client requested the option.
1435 option dhcp6.bcms-server-d domain-list;
1437 The bcms-server-d option contains the domain names of local BCMS
1439 (Broadcast and Multicast Control Services) controllers which the
1440 client may use.
1441 option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;
1443 The bcms-server-a option contains the IPv6 addresses of local BCMS
1445 (Broadcast and Multicast Control Services) controllers which the
1446 client may use.
1447 option dhcp6.geoconf-civic string;
1449 A string to hold the geoconf civic structure.
1451 This option is included based on RFC 4776.
1453 option dhcp6.remote-id string;
1455 The remote-id option is constructed by relay agents, to inform the
1457 server of details pertaining to what the relay knows about the client
1458 (such as what port it is attached to, and so forth). The contents of
1459 this option have some vendor-specific structure (similar to VSIO),
1460 but we have chosen to treat this option as an opaque field.
1461 option dhcp6.subscriber-id string;
1463 The subscriber-id option is an opaque field provided by the relay
1465 agent, which provides additional information about the subscriber in
1466 question. The exact contents of this option depend upon the vendor
1467 and/or the operator's configuration of the remote device, and as such
1468 is an opaque field.
1469 option dhcp6.fqdn string;
1471 The fqdn option is normally constructed by the client or server, and
1473 negotiates the client's Fully Qualified Domain Name, as well as which
1474 party is responsible for Dynamic DNS Updates. See the section on the
1475 Client FQDN SubOptions for full details (the DHCPv4 and DHCPv6 FQDN
1476 options use the same "fqdn." encapsulated space, so are in all ways
1477 identical).
1478 option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;
1480 A set of IPv6 addresses of a PAA for the client to use. The ad‐
1482 dresses are listed in preferred order.
1483 This option is included based on RFC 5192.
1485 option dhcp6.new-posix-timezone text;
1487 This option specifies a string suitable for the TZ variable.
1489 This option is included based on RFC 4833.
1491 option dhcp6.new-tzdb-timezone text;
1493 This option specifies a name of a zone entry in the TZ database.
1495 This option is included based on RFC 4833.
1497 option dhcp6.ero uint16 [, uint16 ... ] ;
1499 A list of the options requested by the relay agent.
1501 This option is included based on RFC 4994.
1503 option dhcp6.lq-query string;
1505 The lq-query option is used internally for lease query.
1507 option dhcp6.client-data string;
1509 The client-data option is used internally for lease query.
1511 option dhcp6.clt-time uint32;
1513 The clt-time option is used internally for lease query.
1515 option dhcp6.lq-relay-data ip6-address string;
1517 The lq-relay-data option is used internally for lease query.
1519 option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;
1521 The lq-client-link option is used internally for lease query.
1523 option dhcp6.v6-lost domain-name;
1525 The domain name of the LoST server for the client to use.
1527 This option is included based on RFC 5223.
1529 option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;
1531 A list of IPv6 addresses of CAPWAP ACs that the WTP may use. The ad‐
1533 dresses are listed in preference order.
1534 This option is included based on RFC 5417.
1536 option dhcp6.relay-id string;
1538 The DUID for the relay agent.
1540 This option is included based on RFC 5460.
1542 option dhcp6.v6-access-domain domain-name;
1544 The domain name associated with the access network for use with LIS
1546 Discovery.
1547 This option is included based on RFC5986.
1549 option dhcp6.sip-ua-cs-list domain-list;
1551 The list of domain names in the SIP User Agent Configuration Service
1553 Domains.
1554 This option is included based on RFC 6011.
1556 option dhcp6.bootfile-url text;
1558 The URL for a boot file.
1560 This option is included based on RFC 5970.
1562 option dhcp6.bootfile-param string;
1564 A string for the parameters to the bootfile. See RFC 5970 for more
1566 description of the layout of the parameters within the string.
1567 This option is included based on RFC 5970.
1569 option dhcp6.client-arch-type uint16 [, uint16 ... ] ;
1571 A list of one or more architecture types described as 16 bit values.
1573 This option is included based on RFC 5970.
1575 option dhcp6.nii uint8 uint8 uint8;
1577 The client network interface identitier option supplies information
1579 about a client's level of UNDI support. The values are, in order,
1580 the type, the major value and the minor value.
1581 This option is included based on RFC5970.
1583 option dhcp6.aftr-name domain-name;
1585 A domain name of the AFTR tunnel endpoint.
1587 This option is included based on RFC 6334.
1589 option dhcp6.erp-local-domain-name domain-name;
1591 A domain name for the ERP domain.
1593 This option is included based on RFC 6440.
1595 option dhcp6.rdnss-selection ip6-address uint8 domain-name;
1597 RDNSS information consists of an IPv6 address of RDNSS, an 8 bit
1599 flags field and a domain-list of domains for which the RDNSS has spe‐
1600 cial knowledge.
1601 This option is included based on RFC 6731.
1603 option dhcp6.client-linklayer-addr string;
1605 A client link-layer address. The first two bytes must be the type of
1607 the link-layer followed by the address itself.
1608 This option is included based on RFC 6939.
1610 option dhcp6.link-address ip6-address;
1612 An IPv6 address used by a relay agent to indicate to the server the
1614 link on which the client is located.
1615 This option is included based on RFC 6977.
1617 option dhcp6.solmax-rt uint32;
1619 A value to override the default for SOL_MAX_RT. This is a 32 bit
1621 value.
1622 This option is included based on RFC 7083.
1624 option dhcp6.inf-max-rt uint32;
1626 A value to override the default for INF_MAX_RT. This is a 32 bit
1628 value.
1629 This option is included based on RFC 7083.
1631
1633 v6relay (relay-number, option) This option allows access to an option
1634 that has been added to a packet by a relay agent. Relay-number value
1635 selects the relay to examine and option is the option to find. In
1636 DHCPv6 each relay encapsulates the entire previous message into an op‐
1637 tion, adds its own options (if any) and sends the result onwards. The
1638 RFC specifies a limit of 32 hops. A relay-number of 0 is a no-op and
1639 means don't look at the relays. 1 is the relay that is closest to the
1640 client, 2 would be the next in from the client and so on. Any value
1641 greater than the max number of hops is which is closest to the server
1642 independent of number. To use this option in a class statement you
1643 would have something like this:
1644 match if v6relay(1, option dhcp6.subscriber-id) = "client_1";
1646
1648 The Internet Systems Consortium DHCP client and server provide the ca‐
1649 pability to define new options. Each DHCP option has a name, a code,
1650 and a structure. The name is used by you to refer to the option. The
1651 code is a number, used by the DHCP server and client to refer to an op‐
1652 tion. The structure describes what the contents of an option looks
1653 like.
1654 To define a new option, you need to choose a name for it that is not in
1656 use for some other option - for example, you can't use "host-name" be‐
1657 cause the DHCP protocol already defines a host-name option, which is
1658 documented earlier in this manual page. If an option name doesn't ap‐
1659 pear in this manual page, you can use it, but it's probably a good idea
1660 to put some kind of unique string at the beginning so you can be sure
1661 that future options don't take your name. For example, you might de‐
1662 fine an option, "local-host-name", feeling some confidence that no of‐
1663 ficial DHCP option name will ever start with "local".
1664 Once you have chosen a name, you must choose a code. All codes between
1666 224 and 254 are reserved as ´site-local´ DHCP options, so you can pick
1667 any one of these for your site (not for your product/application). In
1668 RFC3942, site-local space was moved from starting at 128 to starting at
1669 224. In practice, some vendors have interpreted the protocol rather
1670 loosely and have used option code values greater than 128 themselves.
1671 There's no real way to avoid this problem, and it was thought to be un‐
1672 likely to cause too much trouble in practice. If you come across a
1673 vendor-documented option code in either the new or old site-local spa‐
1674 ces, please contact your vendor and inform them about rfc3942.
1675 The structure of an option is simply the format in which the option
1677 data appears. The ISC DHCP server currently supports a few simple
1678 types, like integers, booleans, strings and IP addresses, and it also
1679 supports the ability to define arrays of single types or arrays of
1680 fixed sequences of types.
1681 New options are declared as follows:
1683 option new-name code new-code = definition ;
1685 The values of new-name and new-code should be the name you have chosen
1687 for the new option and the code you have chosen. The definition should
1688 be the definition of the structure of the option.
1689 The following simple option type definitions are supported:
1691 BOOLEAN
1693 option new-name code new-code = boolean ;
1695 An option of type boolean is a flag with a value of either on or off
1697 (or true or false). So an example use of the boolean type would be:
1698 option use-zephyr code 180 = boolean;
1700 option use-zephyr on;
1701 INTEGER
1703 option new-name code new-code = sign integer width ;
1705 The sign token should either be blank, unsigned or signed. The width
1707 can be either 8, 16 or 32, and refers to the number of bits in the in‐
1708 teger. So for example, the following two lines show a definition of
1709 the sql-connection-max option and its use:
1710 option sql-connection-max code 192 = unsigned integer 16;
1712 option sql-connection-max 1536;
1713 IP-ADDRESS
1715 option new-name code new-code = ip-address ;
1717 An option whose structure is an IP address can be expressed either as a
1719 domain name or as a dotted quad. So the following is an example use of
1720 the ip-address type:
1721 option sql-server-address code 193 = ip-address;
1723 option sql-server-address sql.example.com;
1724 IP6-ADDRESS
1726 option new-name code new-code = ip6-address ;
1728 An option whose structure is an IPv6 address must be expressed as a
1730 valid IPv6 address. The following is an example use of the ip6-address
1731 type:
1732 option dhcp6.some-server code 1234 = array of ip6-address;
1734 option dhcp6.some-server 3ffe:bbbb:aaaa:aaaa::1, 3ffe:bbbb:aaaa:aaaa::2;
1735 TEXT
1738 option new-name code new-code = text ;
1740 An option whose type is text will encode an ASCII text string. For ex‐
1742 ample:
1743 option sql-default-connection-name code 194 = text;
1745 option sql-default-connection-name "PRODZA";
1746 DATA STRING
1749 option new-name code new-code = string ;
1751 An option whose type is a data string is essentially just a collection
1753 of bytes, and can be specified either as quoted text, like the text
1754 type, or as a list of hexadecimal contents separated by colons whose
1755 values must be between 0 and FF. For example:
1756 option sql-identification-token code 195 = string;
1758 option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;
1759 DOMAIN-LIST
1762 option new-name code new-code = domain-list [compressed] ;
1764 An option whose type is domain-list is an RFC1035 formatted (on the
1766 wire, "DNS Format") list of domain names, separated by root labels.
1767 The optional compressed keyword indicates if the option should be com‐
1768 pressed relative to the start of the option contents (not the packet
1769 contents).
1770 When in doubt, omit the compressed keyword. When the software receives
1772 an option that is compressed and the compressed keyword is omitted, it
1773 will still decompress the option (relative to the option contents
1774 field). The keyword only controls whether or not transmitted packets
1775 are compressed.
1776 Note that when domain-list formatted options are output as environment
1778 variables to dhclient-script(8), the standard DNS -escape mechanism is
1779 used: they are decimal. This is appropriate for direct use in eg
1780 /etc/resolv.conf.
1781 ENCAPSULATION
1784 option new-name code new-code = encapsulate identifier ;
1786 An option whose type is encapsulate will encapsulate the contents of
1788 the option space specified in identifier. Examples of encapsulated op‐
1789 tions in the DHCP protocol as it currently exists include the vendor-
1790 encapsulated-options option, the netware-suboptions option and the re‐
1791 lay-agent-information option.
1792 option space local;
1794 option local.demo code 1 = text;
1795 option local-encapsulation code 197 = encapsulate local;
1796 option local.demo "demo";
1797 ARRAYS
1800 Options can contain arrays of any of the above types except for the
1802 text and data string types, which aren't currently supported in arrays.
1803 An example of an array definition is as follows:
1804 option kerberos-servers code 200 = array of ip-address;
1806 option kerberos-servers 10.20.10.1, 10.20.11.1;
1807 RECORDS
1809 Options can also contain data structures consisting of a sequence of
1811 data types, which is sometimes called a record type. For example:
1812 option contrived-001 code 201 = { boolean, integer 32, text };
1814 option contrived-001 on 1772 "contrivance";
1815 It's also possible to have options that are arrays of records, for ex‐
1817 ample:
1818 option new-static-routes code 201 = array of {
1820 ip-address, ip-address, ip-address, integer 8 };
1821 option static-routes
1822 10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
1823 10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
1824 10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;
1825
1828 The DHCP protocol defines the vendor-encapsulated-options option, which
1829 allows vendors to define their own options that will be sent encapsu‐
1830 lated in a standard DHCP option. It also defines the Vendor Identified
1831 Vendor Sub Options option ("VIVSO"), and the DHCPv6 protocol defines
1832 the Vendor-specific Information Option ("VSIO"). The format of all of
1833 these options is usually internally a string of options, similarly to
1834 other normal DHCP options. The VIVSO and VSIO options differ in that
1835 they contain options that correspond to vendor Enterprise-ID numbers
1836 (assigned by IANA), which then contain options according to each Ven‐
1837 dor's specifications. You will need to refer to your vendor's documen‐
1838 tation in order to form options to their specification.
1839 The value of these options can be set in one of two ways. The first
1841 way is to simply specify the data directly, using a text string or a
1842 colon-separated list of hexadecimal values. For help in forming these
1843 strings, please refer to RFC2132 for the DHCPv4 Vendor Specific Infor‐
1844 mation Option, RFC3925 for the DHCPv4 Vendor Identified Vendor Sub Op‐
1845 tions, or RFC3315 for the DHCPv6 Vendor-specific Information Option.
1846 For example:
1847 option vendor-encapsulated-options
1849 2:4:
1850 AC:11:41:1:
1851 3:12:
1852 73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
1853 4:12:
1854 2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
1855 option vivso
1856 00:00:09:bf:0E:
1857 01:0c:
1858 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1859 option dhcp6.vendor-opts
1860 00:00:09:bf:
1861 00:01:00:0c:
1862 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1863 The second way of setting the value of these options is to have the
1865 DHCP server generate a vendor-specific option buffer. To do this, you
1866 must do four things: define an option space, define some options in
1867 that option space, provide values for them, and specify that that op‐
1868 tion space should be used to generate the relevant option.
1869 To define a new option space in which vendor options can be stored, use
1871 the option space statement:
1872 option space name [ [ code width number ] [ length width number ] [
1874 hash size number ] ] ;
1875 Where the numbers following code width, length width, and hash size re‐
1877 spectively identify the number of bytes used to describe option codes,
1878 option lengths, and the size in buckets of the hash tables to hold op‐
1879 tions in this space (most DHCPv4 option spaces use 1 byte codes and
1880 lengths, which is the default, whereas most DHCPv6 option spaces use 2
1881 byte codes and lengths).
1882 The code and length widths are used in DHCP protocol - you must config‐
1884 ure these numbers to match the applicable option space you are config‐
1885 uring. They each default to 1. Valid values for code widths are 1, 2
1886 or 4. Valid values for length widths are 0, 1 or 2. Most DHCPv4 op‐
1887 tion spaces use 1 byte codes and lengths, which is the default, whereas
1888 most DHCPv6 option spaces use 2 byte codes and lengths. A zero-byte
1889 length produces options similar to the DHCPv6 Vendor-specific Informa‐
1890 tion Option - but not their contents!
1891 The hash size defaults depend upon the code width selected, and may be
1893 254 or 1009. Valid values range between 1 and 65535. Note that the
1894 higher you configure this value, the more memory will be used. It is
1895 considered good practice to configure a value that is slightly larger
1896 than the estimated number of options you plan to configure within the
1897 space. Previous versions of ISC DHCP (up to and including DHCP 3.0.*),
1898 this value was fixed at 9973.
1899 The name can then be used in option definitions, as described earlier
1901 in this document. For example:
1902 option space SUNW code width 1 length width 1 hash size 3;
1904 option SUNW.server-address code 2 = ip-address;
1905 option SUNW.server-name code 3 = text;
1906 option SUNW.root-path code 4 = text;
1907 option space ISC code width 1 length width 1 hash size 3;
1909 option ISC.sample code 1 = text;
1910 option vendor.ISC code 2495 = encapsulate vivso-sample;
1911 option vendor-class.ISC code 2495 = text;
1912 option ISC.sample "configuration text here";
1914 option vendor-class.ISC "vendor class here";
1915 option space docsis code width 2 length width 2 hash size 17;
1917 option docsis.tftp-servers code 32 = array of ip6-address;
1918 option docsis.cablelabs-configuration-file code 33 = text;
1919 option docsis.cablelabs-syslog-servers code 34 = array of ip6-address;
1920 option docsis.device-id code 36 = string;
1921 option docsis.time-servers code 37 = array of ip6-address;
1922 option docsis.time-offset code 38 = signed integer 32;
1923 option vsio.docsis code 4491 = encapsulate docsis;
1924 Once you have defined an option space and the format of some options,
1926 you can set up scopes that define values for those options, and you can
1927 say when to use them. For example, suppose you want to handle two dif‐
1928 ferent classes of clients. Using the option space definition shown in
1929 the previous example, you can send different option values to different
1930 clients based on the vendor-class-identifier option that the clients
1931 send, as follows:
1932 class "vendor-classes" {
1934 match option vendor-class-identifier;
1935 }
1936 subclass "vendor-classes" "SUNW.Ultra-5_10" {
1938 vendor-option-space SUNW;
1939 option SUNW.root-path "/export/root/sparc";
1940 }
1941 subclass "vendor-classes" "SUNW.i86pc" {
1943 vendor-option-space SUNW;
1944 option SUNW.root-path "/export/root/i86pc";
1945 }
1946 option SUNW.server-address 172.17.65.1;
1948 option SUNW.server-name "sundhcp-server17-1";
1949 option vivso-sample.sample "Hello world!";
1951 option docsis.tftp-servers ::1;
1953 As you can see in the preceding example, regular scoping rules apply,
1956 so you can define values that are global in the global scope, and only
1957 define values that are specific to a particular class in the local
1958 scope. The vendor-option-space declaration tells the DHCP server to
1959 use options in the SUNW option space to construct the DHCPv4 vendor-en‐
1960 capsulated-options option. This is a limitation of that option - the
1961 DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi‐
1962 nitions all at once (even transmitted to the same client), so it is not
1963 necessary to configure this.
1964
1966 dhcpd.conf(5), dhcpd.leases(5), dhclient.conf(5), dhcp-eval(5),
1967 dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.
1968
1970 Information about Internet Systems Consortium can be found at
1971 https://www.isc.org.
1972 dhcp-options(5)