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. 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
32 resolve it while responding to the first client query dhcpd receives
33 after startup. Should the domain's address subsequently change, the
34 software 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
46 enclosed 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
109 option you would edit the includes/site.h file and comment out the def‐
110 inition 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
115 below may not yet be implemented, but it is possible to use such
116 options by defining them in the configuration file. Please see the
117 DEFINING NEW OPTIONS heading later in this document for more informa‐
118 tion.
119 Some of the options documented here are automatically generated by the
121 DHCP server or by clients, and cannot be configured by the user. The
122 value of such an option can be used in the configuration file of the
123 receiving DHCP protocol agent (server or client), for example in condi‐
124 tional expressions. However, the value of the option cannot be used in
125 the configuration file of the sending agent, because the value is
126 determined only after the configuration file has been processed. In the
127 following documentation, such options will be shown as "not user con‐
128 figurable"
129 The standard options are:
131 option all-subnets-local flag;
133 This option specifies whether or not the client may assume that all
135 subnets of the IP network to which the client is connected use the
136 same MTU as the subnet of that network to which the client is
137 directly connected. A value of true indicates that all subnets share
138 the same MTU. A value of false means that the client should assume
139 that some subnets of the directly connected network may have smaller
140 MTUs.
141 option arp-cache-timeout uint32;
143 This option specifies the timeout in seconds for ARP cache entries.
145 option associated-ip ip-address [, ip-address... ];
147 This option is part of lease query. It is used to return all of the
149 IP addresses associated with a given DHCP client.
150 This option is not user configurable.
152 option bcms-controller-address ip-address [, ip-address... ];
154 This option configures a list of IPv4 addresses for use as Broadcast
156 and Multicast Controller Servers ("BCMS").
157 option bcms-controller-names domain-list;
159 This option contains the domain names of local Broadcast and Multi‐
161 cast Controller Servers ("BCMS") controllers which the client may
162 use.
163 option bootfile-name text;
165 This option is used to identify a bootstrap file. If supported by
167 the client, it should have the same effect as the filename declara‐
168 tion. BOOTP clients are unlikely to support this option. Some DHCP
169 clients will support it, and others actually require it.
170 option boot-size uint16;
172 This option specifies the length in 512-octet blocks of the default
174 boot image for the client.
175 option broadcast-address ip-address;
177 This option specifies the broadcast address in use on the client's
179 subnet. Legal values for broadcast addresses are specified in sec‐
180 tion 3.2.1.3 of STD 3 (RFC1122).
181 option capwap-ac-v4 ip-address [, ip-address ... ] ;
183 A list of IPv4 addresses of CAPWAP ACs that the WTP may use. The
185 addresses are listed in preference order.
186 This option is included based on RFC 5417.
188 option client-last-transaction-time uint32;
190 This option is part of lease query. It allows the receiver to deter‐
192 mine the time of the most recent access by the client. The value is
193 a duration in seconds from when the client last communicated with the
194 DHCP server.
195 This option is not user configurable.
197 option cookie-servers ip-address [, ip-address... ];
199 The cookie server option specifies a list of RFC 865 cookie servers
201 available to the client. Servers should be listed in order of pref‐
202 erence.
203 option default-ip-ttl uint8;
205 This option specifies the default time-to-live that the client should
207 use on outgoing datagrams.
208 option default-tcp-ttl uint8;
210 This option specifies the default TTL that the client should use when
212 sending TCP segments. The minimum value is 1.
213 option default-url string;
215 The format and meaning of this option is not described in any stan‐
217 dards document, but is claimed to be in use by Apple Computer. It is
218 not known what clients may reasonably do if supplied with this
219 option. Use at your own risk.
220 option dhcp-client-identifier string;
222 This option can be used to specify a DHCP client identifier in a host
224 declaration, so that dhcpd can find the host record by matching
225 against the client identifier.
226 Please be aware that some DHCP clients, when configured with client
228 identifiers that are ASCII text, will prepend a zero to the ASCII
229 text. So you may need to write:
230 option dhcp-client-identifier "\0foo";
232 rather than:
234 option dhcp-client-identifier "foo";
236 option dhcp-lease-time uint32;
238 This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
240 to allow the client to request a lease time for the IP address. In a
241 server reply (DHCPOFFER), a DHCP server uses this option to specify
242 the lease time it is willing to offer.
243 This option is not directly user configurable in the server; refer to
245 the max-lease-time and default-lease-time server options in
246 dhcpd.conf(5).
247 option dhcp-max-message-size uint16;
249 This option, when sent by the client, specifies the maximum size of
251 any response that the server sends to the client. When specified on
252 the server, if the client did not send a dhcp-max-message-size
253 option, the size specified on the server is used. This works for
254 BOOTP as well as DHCP responses.
255 option dhcp-message text;
257 This option is used by a DHCP server to provide an error message to a
259 DHCP client in a DHCPNAK message in the event of a failure. A client
260 may use this option in a DHCPDECLINE message to indicate why the
261 client declined the offered parameters.
262 This option is not user configurable.
264 option dhcp-message-type uint8;
266 This option, sent by both client and server, specifies the type of
268 DHCP message contained in the DHCP packet. Possible values (taken
269 directly from RFC2132) are:
270 1 DHCPDISCOVER
272 2 DHCPOFFER
273 3 DHCPREQUEST
274 4 DHCPDECLINE
275 5 DHCPACK
276 6 DHCPNAK
277 7 DHCPRELEASE
278 8 DHCPINFORM
279 This option is not user configurable.
281 option dhcp-option-overload uint8;
283 This option is used to indicate that the DHCP ´sname´ or ´file´
285 fields are being overloaded by using them to carry DHCP options. A
286 DHCP server inserts this option if the returned parameters will
287 exceed the usual space allotted for options.
288 If this option is present, the client interprets the specified addi‐
290 tional fields after it concludes interpretation of the standard
291 option fields.
292 Legal values for this option are:
294 1 the ´file´ field is used to hold options
296 2 the ´sname´ field is used to hold options
297 3 both fields are used to hold options
298 This option is not user configurable.
300 option dhcp-parameter-request-list uint8 [, uint8... ];
302 This option, when sent by the client, specifies which options the
304 client wishes the server to return. Normally, in the ISC DHCP
305 client, this is done using the request statement. If this option is
306 not specified by the client, the DHCP server will normally return
307 every option that is valid in scope and that fits into the reply.
308 When this option is specified on the server, the server returns the
309 specified options. This can be used to force a client to take
310 options that it hasn't requested, and it can also be used to tailor
311 the response of the DHCP server for clients that may need a more lim‐
312 ited set of options than those the server would normally return.
313 option dhcp-rebinding-time uint32;
315 This option specifies the number of seconds from the time a client
317 gets an address until the client transitions to the REBINDING state.
318 This option is user configurable, but it will be ignored if the value
320 is greater than or equal to the lease time.
321 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
323 figured in this option is also used as a DHCPv6 "T1" (renew) time.
324 option dhcp-renewal-time uint32;
326 This option specifies the number of seconds from the time a client
328 gets an address until the client transitions to the RENEWING state.
329 This option is user configurable, but it will be ignored if the value
331 is greater than or equal to the rebinding time, or lease time.
332 To make DHCPv4+DHCPv6 migration easier in the future, any value con‐
334 figured in this option is also used as a DHCPv6 "T2" (rebind) time.
335 option dhcp-requested-address ip-address;
337 This option is used by the client in a DHCPDISCOVER to request that a
339 particular IP address be assigned.
340 This option is not user configurable.
342 option dhcp-server-identifier ip-address;
344 This option is used in DHCPOFFER and DHCPREQUEST messages, and may
346 optionally be included in the DHCPACK and DHCPNAK messages. DHCP
347 servers include this option in the DHCPOFFER in order to allow the
348 client to distinguish between lease offers. DHCP clients use the
349 contents of the ´server identifier´ field as the destination address
350 for any DHCP messages unicast to the DHCP server. DHCP clients also
351 indicate which of several lease offers is being accepted by including
352 this option in a DHCPREQUEST message.
353 The value of this option is the IP address of the server.
355 This option is not directly user configurable. See the server-identi‐
357 fier server option in dhcpd.conf(5).
358 option domain-name text;
360 This option specifies the domain name that client should use when
362 resolving hostnames via the Domain Name System.
363 option domain-name-servers ip-address [, ip-address... ];
365 The domain-name-servers option specifies a list of Domain Name System
367 (STD 13, RFC 1035) name servers available to the client. Servers
368 should be listed in order of preference.
369 option domain-search domain-list;
371 The domain-search option specifies a ´search list´ of Domain Names to
373 be used by the client to locate not-fully-qualified domain names.
374 The difference between this option and historic use of the domain-
375 name option for the same ends is that this option is encoded in
376 RFC1035 compressed labels on the wire. For example:
377 option domain-search "example.com", "sales.example.com",
379 "eng.example.com";
380 option extensions-path text;
382 This option specifies the name of a file containing additional
384 options to be interpreted according to the DHCP option format as
385 specified in RFC2132.
386 option finger-server ip-address [, ip-address... ];
388 The Finger server option specifies a list of Finger servers available
390 to the client. Servers should be listed in order of preference.
391 option font-servers ip-address [, ip-address... ];
393 This option specifies a list of X Window System Font servers avail‐
395 able to the client. Servers should be listed in order of preference.
396 option geoconf-civic string;
398 A string to hold the geoconf civic structure.
400 This option is included based on RFC 4776.
402 option host-name string;
404 This option specifies the name of the client. The name may or may
406 not be qualified with the local domain name (it is preferable to use
407 the domain-name option to specify the domain name). See RFC 1035 for
408 character set restrictions. This option is only honored by dhclient-
409 script(8) if the hostname for the client machine is not set.
410 option ieee802-3-encapsulation flag;
412 This option specifies whether or not the client should use Ethernet
414 Version 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the
415 interface is an Ethernet. A value of false indicates that the client
416 should use RFC 894 encapsulation. A value of true means that the
417 client should use RFC 1042 encapsulation.
418 option ien116-name-servers ip-address [, ip-address... ];
420 The ien116-name-servers option specifies a list of IEN 116 name
422 servers available to the client. Servers should be listed in order
423 of preference.
424 option impress-servers ip-address [, ip-address... ];
426 The impress-server option specifies a list of Imagen Impress servers
428 available to the client. Servers should be listed in order of pref‐
429 erence.
430 option interface-mtu uint16;
432 This option specifies the MTU to use on this interface. The minimum
434 legal value for the MTU is 68.
435 option ip-forwarding flag;
437 This option specifies whether the client should configure its IP
439 layer for packet forwarding. A value of false means disable IP for‐
440 warding, and a value of true means enable IP forwarding.
441 option irc-server ip-address [, ip-address... ];
443 The IRC server option specifies a list of IRC servers available to
445 the client. Servers should be listed in order of preference.
446 option loader-configfile text
449 This option is used to specify a boot loading configuration file a
451 PXE client should use.
452 This option is included based on RFC 5071.
454 option loader-pathprefix text
456 This option is used to specify a path prefix a PXE client should use
458 in conjunction with the boot load configuration file.
459 This option is included based on RFC 5071.
461 option loader-reboottime uint32
463 This option is used to dictate the maximum amount of time a PXE
465 client should allow itself to achieve configured network resources
466 before rebooting.
467 This option is included based on RFC 5071.
469 option log-servers ip-address [, ip-address... ];
471 The log-server option specifies a list of MIT-LCS UDP log servers
473 available to the client. Servers should be listed in order of pref‐
474 erence.
475 option lpr-servers ip-address [, ip-address... ];
477 The LPR server option specifies a list of RFC 1179 line printer
479 servers available to the client. Servers should be listed in order
480 of preference.
481 option mask-supplier flag;
483 This option specifies whether or not the client should respond to
485 subnet mask requests using ICMP. A value of false indicates that the
486 client should not respond. A value of true means that the client
487 should respond.
488 option max-dgram-reassembly uint16;
490 This option specifies the maximum size datagram that the client
492 should be prepared to reassemble. The minimum legal value is 576.
493 option merit-dump text;
495 This option specifies the path-name of a file to which the client's
497 core image should be dumped in the event the client crashes. The
498 path is formatted as a character string consisting of characters from
499 the NVT ASCII character set.
500 option mobile-ip-home-agent ip-address [, ip-address... ];
502 This option specifies a list of IP addresses indicating mobile IP
504 home agents available to the client. Agents should be listed in
505 order of preference, although normally there will be only one such
506 agent.
507 option name-service-search uint16 [, uint6... ];
509 This option specifies a list of name services in the order the client
511 should attempt to use them.
512 This option is included based on RFC 2937.
514 option nds-context string;
516 The nds-context option specifies the name of the initial Netware
518 Directory Service for an NDS client.
519 option nds-servers ip-address [, ip-address... ];
521 The nds-servers option specifies a list of IP addresses of NDS
523 servers.
524 option nds-tree-name string;
526 The nds-tree-name option specifies NDS tree name that the NDS client
528 should use.
529 option netbios-dd-server ip-address [, ip-address... ];
531 The NetBIOS datagram distribution server (NBDD) option specifies a
533 list of RFC 1001/1002 NBDD servers listed in order of preference.
534 option netbios-name-servers ip-address [, ip-address...];
536 The NetBIOS name server (NBNS) option specifies a list of RFC
538 1001/1002 NBNS name servers listed in order of preference. NetBIOS
539 Name Service is currently more commonly referred to as WINS. WINS
540 servers can be specified using the netbios-name-servers option.
541 option netbios-node-type uint8;
543 The NetBIOS node type option allows NetBIOS over TCP/IP clients which
545 are configurable to be configured as described in RFC 1001/1002. The
546 value is specified as a single octet which identifies the client
547 type.
548 Possible node types are:
550 1 B-node: Broadcast - no WINS
552 2 P-node: Peer - WINS only
554 4 M-node: Mixed - broadcast, then WINS
556 8 H-node: Hybrid - WINS, then broadcast
558 option netbios-scope string;
560 The NetBIOS scope option specifies the NetBIOS over TCP/IP scope
562 parameter for the client as specified in RFC 1001/1002. See RFC1001,
563 RFC1002, and RFC1035 for character-set restrictions.
564 option netinfo-server-address ip-address [, ip-address... ];
566 The netinfo-server-address option has not been described in any RFC,
568 but has been allocated (and is claimed to be in use) by Apple Comput‐
569 ers. It's hard to say if the above is the correct format, or what
570 clients might be expected to do if values were configured. Use at
571 your own risk.
572 option netinfo-server-tag text;
574 The netinfo-server-tag option has not been described in any RFC, but
576 has been allocated (and is claimed to be in use) by Apple Computers.
577 It's hard to say if the above is the correct format, or what clients
578 might be expected to do if values were configured. Use at your own
579 risk.
580 option nis-domain text;
582 This option specifies the name of the client's NIS (Sun Network
584 Information Services) domain. The domain is formatted as a character
585 string consisting of characters from the NVT ASCII character set.
586 option nis-servers ip-address [, ip-address... ];
588 This option specifies a list of IP addresses indicating NIS servers
590 available to the client. Servers should be listed in order of pref‐
591 erence.
592 option nisplus-domain text;
594 This option specifies the name of the client's NIS+ domain. The
596 domain is formatted as a character string consisting of characters
597 from the NVT ASCII character set.
598 option nisplus-servers ip-address [, ip-address... ];
600 This option specifies a list of IP addresses indicating NIS+ servers
602 available to the client. Servers should be listed in order of pref‐
603 erence.
604 option nntp-server ip-address [, ip-address... ];
606 The NNTP server option specifies a list of NNTP servers available to
608 the client. Servers should be listed in order of preference.
609 option non-local-source-routing flag;
611 This option specifies whether the client should configure its IP
613 layer to allow forwarding of datagrams with non-local source routes
614 (see Section 3.3.5 of [4] for a discussion of this topic). A value
615 of false means disallow forwarding of such datagrams, and a value of
616 true means allow forwarding.
617 option ntp-servers ip-address [, ip-address... ];
619 This option specifies a list of IP addresses indicating NTP (RFC
621 5905) servers available to the client. Servers should be listed in
622 order of preference.
623 option nwip-domain string;
625 The name of the NetWare/IP domain that a NetWare/IP client should
627 use.
628 option nwip-suboptions string;
630 A sequence of suboptions for NetWare/IP clients - see RFC2242 for
632 details. Normally this option is set by specifying specific Net‐
633 Ware/IP suboptions - see the NETWARE/IP SUBOPTIONS section for more
634 information.
635 option pxe-system-type uint16 [, uint16 ... ];
637 A list of one ore more 16-bit integers which allows a client to spec‐
639 ify its pre-boot architecture type(s).
640 This option is included based on RFC 4578.
642 option pxe-interface-id uint8 uint8 uint8
644 A three octet value which allows a client to specify its network
646 interface type.
647 This option is included based on RFC 4578.
649 option pxe-client-id uint8 string
651 A single octet indicating type, followed by a string that allows a
653 client to specify its PXE client identity.
654 This option is included based on RFC 4578.
656 option option-6rd uint8 uint8 ip6-address ip-address [, ip-address
658 ...];
659 This option contains information about the rapid deployment option.
661 It is 8 bits of ipv4 mask length, 8 bits of 6rd prefix length, an
662 ipv6 prefix as an ipv6 address and a list of one or more ipv4
663 addresses.
664 This option is included based on RFC 5969.
666 option pana-agent ip-address [, ip-address ... ] ;
668 A set of IPv4 addresses of a PAA for the client to use. The
670 addresses are listed in preferred order.
671 This option is included based on RFC 5192.
673 option path-mtu-aging-timeout uint32;
675 This option specifies the timeout (in seconds) to use when aging Path
677 MTU values discovered by the mechanism defined in RFC 1191.
678 option path-mtu-plateau-table uint16 [, uint16... ];
680 This option specifies a table of MTU sizes to use when performing
682 Path MTU Discovery as defined in RFC 1191. The table is formatted as
683 a list of 16-bit unsigned integers, ordered from smallest to largest.
684 The minimum MTU value cannot be smaller than 68.
685 option pcode text;
687 This option specifies a string suitable for the TZ variable.
689 This option is included based on RFC 4833.
691 option perform-mask-discovery flag;
693 This option specifies whether or not the client should perform subnet
695 mask discovery using ICMP. A value of false indicates that the
696 client should not perform mask discovery. A value of true means that
697 the client should perform mask discovery.
698 option policy-filter ip-address ip-address
700 [, ip-address ip-address...];
701 This option specifies policy filters for non-local source routing.
703 The filters consist of a list of IP addresses and masks which specify
704 destination/mask pairs with which to filter incoming source routes.
705 Any source routed datagram whose next-hop address does not match one
707 of the filters should be discarded by the client.
708 See STD 3 (RFC1122) for further information.
710 option pop-server ip-address [, ip-address... ];
712 The POP3 server option specifies a list of POP3 servers available to
714 the client. Servers should be listed in order of preference.
715 option rdnss-selection uint8 ip-address ip-address domain-name;
717 The rdnss-selection option specifies an 8 bit flags field, a primary
719 and secondary ip address for the name server and a domainlist of
720 domains for which the RDNSS has special knowledge.
721 This option is included based on RFC 6731.
723 option resource-location-servers ip-address
725 [, ip-address...];
726 This option specifies a list of RFC 887 Resource Location servers
728 available to the client. Servers should be listed in order of pref‐
729 erence.
730 option root-path text;
732 This option specifies the path-name that contains the client's root
734 disk. The path is formatted as a character string consisting of
735 characters from the NVT ASCII character set.
736 option router-discovery flag;
738 This option specifies whether or not the client should solicit
740 routers using the Router Discovery mechanism defined in RFC 1256. A
741 value of false indicates that the client should not perform router
742 discovery. A value of true means that the client should perform
743 router discovery.
744 option router-solicitation-address ip-address;
746 This option specifies the address to which the client should transmit
748 router solicitation requests.
749 option routers ip-address [, ip-address... ];
751 The routers option specifies a list of IP addresses for routers on
753 the client's subnet. Routers should be listed in order of prefer‐
754 ence.
755 option slp-directory-agent boolean ip-address [, ip-address... ];
757 This option specifies two things: the IP addresses of one or more
759 Service Location Protocol Directory Agents, and whether the use of
760 these addresses is mandatory. If the initial boolean value is true,
761 the SLP agent should just use the IP addresses given. If the value
762 is false, the SLP agent may additionally do active or passive multi‐
763 cast discovery of SLP agents (see RFC2165 for details).
764 Please note that in this option and the slp-service-scope option, the
766 term "SLP Agent" is being used to refer to a Service Location Proto‐
767 col agent running on a machine that is being configured using the
768 DHCP protocol.
769 Also, please be aware that some companies may refer to SLP as NDS.
771 If you have an NDS directory agent whose address you need to config‐
772 ure, the slp-directory-agent option should work.
773 option slp-service-scope boolean text;
775 The Service Location Protocol Service Scope Option specifies two
777 things: a list of service scopes for SLP, and whether the use of this
778 list is mandatory. If the initial boolean value is true, the SLP
779 agent should only use the list of scopes provided in this option;
780 otherwise, it may use its own static configuration in preference to
781 the list provided in this option.
782 The text string should be a comma-separated list of scopes that the
784 SLP agent should use. It may be omitted, in which case the SLP Agent
785 will use the aggregated list of scopes of all directory agents known
786 to the SLP agent.
787 option smtp-server ip-address [, ip-address... ];
789 The SMTP server option specifies a list of SMTP servers available to
791 the client. Servers should be listed in order of preference.
792 option static-routes ip-address ip-address
794 [, ip-address ip-address...];
795 This option specifies a list of static routes that the client should
797 install in its routing cache. If multiple routes to the same desti‐
798 nation are specified, they are listed in descending order of prior‐
799 ity.
800 The routes consist of a list of IP address pairs. The first address
802 is the destination address, and the second address is the router for
803 the destination.
804 The default route (0.0.0.0) is an illegal destination for a static
806 route. To specify the default route, use the routers option. Also,
807 please note that this option is not intended for classless IP routing
808 - it does not include a subnet mask. Since classless IP routing is
809 now the most widely deployed routing standard, this option is virtu‐
810 ally useless, and is not implemented by any of the popular DHCP
811 clients, for example the Microsoft DHCP client.
812 NOTE to Fedora dhclient users:
814 dhclient-script interprets trailing 0 octets of the target as indi‐
815 cating the subnet class of the route, so for the following static-
816 routes value:
817 option static-routes 172.0.0.0 172.16.2.254,
818 192.168.0.0 192.168.2.254;
819 dhclient-script will create routes:
820 172/8 via 172.16.2.254 dev $interface
821 192.168/16 via 192.168.2.254 dev $interface
822 option classless-static-routes destination-descriptor ip-address
824 [, destination-descriptor ip-address...];
825 This option (see RFC3442) specifies a list of classless static routes
827 that the client should install in its routing cache.
828 This option can contain one or more static routes, each of which con‐
830 sists of a destination descriptor and the IP address of the router
831 that should be used to reach that destination.
832 Many clients may not implement the Classless Static Routes option.
834 DHCP server administrators should therefore configure their DHCP
835 servers to send both a Router option and a Classless Static Routes
836 option, and should specify the default router(s) both in the Router
837 option and in the Classless Static Routes option.
838 If the DHCP server returns both a Classless Static Routes option and
840 a Router option, the DHCP client ignores the Router option.
841 option streettalk-directory-assistance-server ip-address
843 [, ip-address...];
844 The StreetTalk Directory Assistance (STDA) server option specifies a
846 list of STDA servers available to the client. Servers should be
847 listed in order of preference.
848 option streettalk-server ip-address [, ip-address... ];
850 The StreetTalk server option specifies a list of StreetTalk servers
852 available to the client. Servers should be listed in order of pref‐
853 erence.
854 option subnet-mask ip-address;
856 The subnet mask option specifies the client's subnet mask as per RFC
858 950. If no subnet mask option is provided anywhere in scope, as a
859 last resort dhcpd will use the subnet mask from the subnet declara‐
860 tion for the network on which an address is being assigned. However,
861 any subnet-mask option declaration that is in scope for the address
862 being assigned will override the subnet mask specified in the subnet
863 declaration.
864 option subnet-selection ip-address;
866 Sent by the client if an address is required in a subnet other than
868 the one that would normally be selected (based on the relaying
869 address of the connected subnet the request is obtained from). See
870 RFC3011. Note that the option number used by this server is 118; this
871 has not always been the defined number, and some clients may use a
872 different value. Use of this option should be regarded as slightly
873 experimental!
874 This option is not user configurable in the server.
876 option swap-server ip-address;
878 This specifies the IP address of the client's swap server.
880 option tftp-server-address ip-address [, ip-address... ];
882 This option configures a list of one or more IPv4 addresses of tftp
884 servers a client may use.
885 This option is included based on RFC 5859
887 option tcp-keepalive-garbage flag;
889 This option specifies whether or not the client should send TCP
891 keepalive messages with an octet of garbage for compatibility with
892 older implementations. A value of false indicates that a garbage
893 octet should not be sent. A value of true indicates that a garbage
894 octet should be sent.
895 option tcp-keepalive-interval uint32;
897 This option specifies the interval (in seconds) that the client TCP
899 should wait before sending a keepalive message on a TCP connection.
900 The time is specified as a 32-bit unsigned integer. A value of zero
901 indicates that the client should not generate keepalive messages on
902 connections unless specifically requested by an application.
903 option tcode text;
905 This option specifies a name of a zone entry in the TZ database.
907 This option is included based on RFC 4833.
909 option tftp-server-name text;
911 This option is used to identify a TFTP server and, if supported by
913 the client, should have the same effect as the server-name declara‐
914 tion. BOOTP clients are unlikely to support this option. Some DHCP
915 clients will support it, and others actually require it.
916 option time-offset int32;
918 The time-offset option specifies the offset of the client's subnet in
920 seconds from Coordinated Universal Time (UTC).
921 option time-servers ip-address [, ip-address... ];
923 The time-server option specifies a list of RFC 868 time servers
925 available to the client. Servers should be listed in order of pref‐
926 erence.
927 option trailer-encapsulation flag;
929 This option specifies whether or not the client should negotiate the
931 use of trailers (RFC 893 [14]) when using the ARP protocol. A value
932 of false indicates that the client should not attempt to use trail‐
933 ers. A value of true means that the client should attempt to use
934 trailers.
935 option uap-servers text;
937 This option specifies a list of URLs, each pointing to a user authen‐
939 tication service that is capable of processing authentication
940 requests encapsulated in the User Authentication Protocol (UAP). UAP
941 servers can accept either HTTP 1.1 or SSLv3 connections. If the list
942 includes a URL that does not contain a port component, the normal
943 default port is assumed (i.e., port 80 for http and port 443 for
944 https). If the list includes a URL that does not contain a path com‐
945 ponent, the path /uap is assumed. If more than one URL is specified
946 in this list, the URLs are separated by spaces.
947 option user-class string;
949 This option is used by some DHCP clients as a way for users to spec‐
951 ify identifying information to the client. This can be used in a
952 similar way to the vendor-class-identifier option, but the value of
953 the option is specified by the user, not the vendor. Most recent
954 DHCP clients have a way in the user interface to specify the value
955 for this identifier, usually as a text string.
956 option v4-access-domain domain-name;
958 The domain name associated with the access network for use with LIS
960 Discovery.
961 This option is included based on RFC 5986.
963 option v4-lost domain-name;
965 The domain name of the LoST server for the client to use.
967 This option is included based on RFC 5223.
969 option vendor-class-identifier string;
971 This option is used by some DHCP clients to identify the vendor type
973 and possibly the configuration of a DHCP client. The information is
974 a string of bytes whose contents are specific to the vendor and are
975 not specified in a standard. To see what vendor class identifier
976 clients are sending, you can write the following in your DHCP server
977 configuration file:
978 set vendor-string = option vendor-class-identifier;
980 This will result in all entries in the DHCP server lease database
982 file for clients that sent vendor-class-identifier options having a
983 set statement that looks something like this:
984 set vendor-string = "SUNW.Ultra-5_10";
986 The vendor-class-identifier option is normally used by the DHCP
988 server to determine the options that are returned in the vendor-
989 encapsulated-options option. Please see the VENDOR ENCAPSULATED
990 OPTIONS section later in this manual page for further information.
991 option vendor-encapsulated-options string;
993 The vendor-encapsulated-options option can contain either a single
995 vendor-specific value or one or more vendor-specific suboptions.
996 This option is not normally specified in the DHCP server configura‐
997 tion file - instead, a vendor class is defined for each vendor, ven‐
998 dor class suboptions are defined, values for those suboptions are
999 defined, and the DHCP server makes up a response on that basis.
1000 Some default behaviours for well-known DHCP client vendors (cur‐
1002 rently, the Microsoft Windows 2000 DHCP client) are configured auto‐
1003 matically, but otherwise this must be configured manually - see the
1004 VENDOR ENCAPSULATED OPTIONS section later in this manual page for
1005 details.
1006 option vivso string;
1008 The vivso option can contain multiple separate options, one for each
1010 32-bit Enterprise ID. Each Enterprise-ID discriminated option then
1011 contains additional options whose format is defined by the vendor who
1012 holds that ID. This option is usually not configured manually, but
1013 rather is configured via intervening option definitions. Please also
1014 see the VENDOR ENCAPSULATED OPTIONS section later in this manual page
1015 for details.
1016 option www-server ip-address [, ip-address... ];
1018 The WWW server option specifies a list of WWW servers available to
1020 the client. Servers should be listed in order of preference.
1021 option x-display-manager ip-address [, ip-address... ];
1023 This option specifies a list of systems that are running the X Window
1025 System Display Manager and are available to the client. Addresses
1026 should be listed in order of preference.
1027
1029 An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
1030 encapsulated options that a relay agent can add to a DHCP packet when
1031 relaying it to the DHCP server. The server can then make address allo‐
1032 cation decisions (or whatever other decisions it wants) based on these
1033 options. The server also returns these options in any replies it sends
1034 through the relay agent, so that the relay agent can use the informa‐
1035 tion in these options for delivery or accounting purposes.
1036 The current draft defines two options. To reference these options in
1038 the dhcp server, specify the option space name, "agent", followed by a
1039 period, followed by the option name. It is not normally useful to
1040 define values for these options in the server, although it is permissi‐
1041 ble. These options are not supported in the client.
1042 option agent.circuit-id string;
1044 The circuit-id suboption encodes an agent-local identifier of the
1046 circuit from which a DHCP client-to-server packet was received. It
1047 is intended for use by agents in relaying DHCP responses back to the
1048 proper circuit. The format of this option is currently defined to be
1049 vendor-dependent, and will probably remain that way, although the
1050 current draft allows for the possibility of standardizing the format
1051 in the future.
1052 option agent.remote-id string;
1054 The remote-id suboption encodes information about the remote host end
1056 of a circuit. Examples of what it might contain include caller ID
1057 information, username information, remote ATM address, cable modem
1058 ID, and similar things. In principal, the meaning is not well-speci‐
1059 fied, and it should generally be assumed to be an opaque object that
1060 is administratively guaranteed to be unique to a particular remote
1061 end of a circuit.
1062 option agent.DOCSIS-device-class uint32;
1064 The DOCSIS-device-class suboption is intended to convey information
1066 about the host endpoint, hardware, and software, that either the host
1067 operating system or the DHCP server may not otherwise be aware of
1068 (but the relay is able to distinguish). This is implemented as a
1069 32-bit field (4 octets), each bit representing a flag describing the
1070 host in one of these ways. So far, only bit zero (being the least
1071 significant bit) is defined in RFC3256. If this bit is set to one,
1072 the host is considered a CPE Controlled Cable Modem (CCCM). All
1073 other bits are reserved.
1074 option agent.link-selection ip-address;
1076 The link-selection suboption is provided by relay agents to inform
1078 servers what subnet the client is actually attached to. This is use‐
1079 ful in those cases where the giaddr (where responses must be sent to
1080 the relay agent) is not on the same subnet as the client. When this
1081 option is present in a packet from a relay agent, the DHCP server
1082 will use its contents to find a subnet declared in configuration, and
1083 from here take one step further backwards to any shared-network the
1084 subnet may be defined within; the client may be given any address
1085 within that shared network, as normally appropriate.
1086
1088 The Client FQDN option, currently defined in the Internet Draft draft-
1089 ietf-dhc-fqdn-option-00.txt is not a standard yet, but is in suffi‐
1090 ciently wide use already that we have implemented it. Due to the com‐
1091 plexity of the option format, we have implemented it as a suboption
1092 space rather than a single option. In general this option should not
1093 be configured by the user - instead it should be used as part of an
1094 automatic DNS update system.
1095 option fqdn.no-client-update flag;
1097 When the client sends this, if it is true, it means the client will
1099 not attempt to update its A record. When sent by the server to the
1100 client, it means that the client should not update its own A record.
1101 option fqdn.server-update flag;
1103 When the client sends this to the server, it is requesting that the
1105 server update its A record. When sent by the server, it means that
1106 the server has updated (or is about to update) the client's A record.
1107 option fqdn.encoded flag;
1109 If true, this indicates that the domain name included in the option
1111 is encoded in DNS wire format, rather than as plain ASCII text. The
1112 client normally sets this to false if it doesn't support DNS wire
1113 format in the FQDN option. The server should always send back the
1114 same value that the client sent. When this value is set on the con‐
1115 figuration side, it controls the format in which the fqdn.fqdn subop‐
1116 tion is encoded.
1117 option fqdn.rcode1 flag;
1119 option fqdn.rcode2 flag;
1121 These options specify the result of the updates of the A and PTR
1123 records, respectively, and are only sent by the DHCP server to the
1124 DHCP client. The values of these fields are those defined in the DNS
1125 protocol specification.
1126 option fqdn.fqdn text;
1128 Specifies the domain name that the client wishes to use. This can be
1130 a fully-qualified domain name, or a single label. If there is no
1131 trailing ´.´ character in the name, it is not fully-qualified, and
1132 the server will generally update that name in some locally-defined
1133 domain.
1134 option fqdn.hostname --never set--;
1136 This option should never be set, but it can be read back using the
1138 option and config-option operators in an expression, in which case it
1139 returns the first label in the fqdn.fqdn suboption - for example, if
1140 the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will
1141 be "foo".
1142 option fqdn.domainname --never set--;
1144 This option should never be set, but it can be read back using the
1146 option and config-option operators in an expression, in which case it
1147 returns all labels after the first label in the fqdn.fqdn suboption -
1148 for example, if the value of fqdn.fqdn is "foo.example.com.", then
1149 fqdn.domainname will be "example.com.". If this suboption value is
1150 not set, it means that an unqualified name was sent in the fqdn
1151 option, or that no fqdn option was sent at all.
1152 If you wish to use any of these suboptions, we strongly recommend that
1154 you refer to the Client FQDN option draft (or standard, when it becomes
1155 a standard) - the documentation here is sketchy and incomplete in com‐
1156 parison, and is just intended for reference by people who already
1157 understand the Client FQDN option specification.
1158
1160 RFC2242 defines a set of encapsulated options for Novell NetWare/IP
1161 clients. To use these options in the dhcp server, specify the option
1162 space name, "nwip", followed by a period, followed by the option name.
1163 The following options can be specified:
1164 option nwip.nsq-broadcast flag;
1166 If true, the client should use the NetWare Nearest Server Query to
1168 locate a NetWare/IP server. The behaviour of the Novell client if
1169 this suboption is false, or is not present, is not specified.
1170 option nwip.preferred-dss ip-address [, ip-address... ];
1172 This suboption specifies a list of up to five IP addresses, each of
1174 which should be the IP address of a NetWare Domain SAP/RIP server
1175 (DSS).
1176 option nwip.nearest-nwip-server ip-address
1178 [, ip-address...];
1179 This suboption specifies a list of up to five IP addresses, each of
1181 which should be the IP address of a Nearest NetWare IP server.
1182 option nwip.autoretries uint8;
1184 Specifies the number of times that a NetWare/IP client should attempt
1186 to communicate with a given DSS server at startup.
1187 option nwip.autoretry-secs uint8;
1189 Specifies the number of seconds that a Netware/IP client should wait
1191 between retries when attempting to establish communications with a
1192 DSS server at startup.
1193 option nwip.nwip-1-1 uint8;
1195 If true, the NetWare/IP client should support NetWare/IP version 1.1
1197 compatibility. This is only needed if the client will be contacting
1198 Netware/IP version 1.1 servers.
1199 option nwip.primary-dss ip-address;
1201 Specifies the IP address of the Primary Domain SAP/RIP Service server
1203 (DSS) for this NetWare/IP domain. The NetWare/IP administration
1204 utility uses this value as Primary DSS server when configuring a sec‐
1205 ondary DSS server.
1206
1208 DHCPv6 options differ from DHCPv4 options partially due to using 16-bit
1209 code and length tags, but semantically zero-length options are legal in
1210 DHCPv6, and multiple options are treated differently. Whereas in
1211 DHCPv4 multiple options would be concatenated to form one option, in
1212 DHCPv6 they are expected to be individual instantiations. Understand‐
1213 ably, many options are not "allowed" to have multiple instances in a
1214 packet - normally these are options which are digested by the DHCP pro‐
1215 tocol software, and not by users or applications.
1216 option dhcp6.client-id string;
1218 This option specifies the client's DUID identifier. DUIDs are simi‐
1220 lar but different from DHCPv4 client identifiers - there are docu‐
1221 mented duid types:
1222 duid-llt
1224 duid-en
1226 duid-ll
1228 This value should not be configured, but rather is provided by
1230 clients and treated as an opaque identifier key blob by servers.
1231 option dhcp6.server-id string;
1233 This option specifies the server's DUID identifier. One may use this
1235 option to configure an opaque binary blob for your server's identi‐
1236 fier.
1237 option dhcp6.ia-na string;
1239 The Identity Association for Non-temporary Addresses (ia-na) carries
1241 assigned addresses that are not temporary addresses for use by the
1242 DHCPv6 client. This option is produced by the DHCPv6 server soft‐
1243 ware, and should not be configured.
1244 option dhcp6.ia-ta string;
1246 The Identity Association for Temporary Addresses (ia-ta) carries tem‐
1248 porary addresses, which may change upon every renewal. There is no
1249 support for this in the current DHCPv6 software.
1250 option dhcp6.ia-addr string;
1252 The Identity Association Address option is encapsulated inside ia-na
1254 or ia-ta options in order to represent addresses associated with
1255 those IA's. These options are manufactured by the software, so
1256 should not be configured.
1257 option dhcp6.oro uint16 [ , uint16, ... ];
1259 The Option Request Option ("ORO") is the DHCPv6 equivalent of the
1261 parameter-request-list. Clients supply this option to ask servers to
1262 reply with options relevant to their needs and use. This option must
1263 not be directly configured, the request syntax in dhclient.conf (5)
1264 should be used instead.
1265 option dhcp6.preference uint8;
1267 The preference option informs a DHCPv6 client which server is ´pre‐
1269 ferred´ for use on a given subnet. This preference is only applied
1270 during the initial stages of configuration - once a client is bound
1271 to an IA, it will remain bound to that IA until it is no longer valid
1272 or has expired. This value may be configured on the server, and is
1273 digested by the client software.
1274 option dhcp6.elapsed-time uint16;
1276 The elapsed-time option is constructed by the DHCPv6 client software,
1278 and is potentially consumed by intermediaries. This option should
1279 not be configured.
1280 option dhcp6.relay-msg string;
1282 The relay-msg option is constructed by intervening DHCPv6 relay agent
1284 software. This option is entirely used by protocol software, and is
1285 not meant for user configuration.
1286 option dhcp6.unicast ip6-address;
1288 The unicast option is provided by DHCPv6 servers which are willing
1290 (or prefer) to receive Request, Renew, Decline, and Release packets
1291 from their clients via unicast. Normally, DHCPv6 clients will multi‐
1292 cast these messages. Per RFC 3315, the server will reject a unicast
1293 message received from a client unless it previously sent (or would
1294 have sent) the unicast option to that client. This option may be
1295 configured on the server at the global and shared network level.
1296 When a unicast message is received, the server will check for an
1297 applicable definition of the unicast option. If such an option is
1298 found the message will be accepted, if not it will be rejected.
1299 option dhcp6.status-code status-code [ string ] ;
1301 The status-code option is provided by DHCPv6 servers to inform
1303 clients of error conditions during protocol communication. This
1304 option is manufactured and digested by protocol software, and should
1305 not be configured.
1306 option dhcp6.rapid-commit ;
1308 The rapid-commit option is a zero-length option that clients use to
1310 indicate their desire to enter into rapid-commit with the server.
1311 option dhcp6.vendor-opts string;
1313 The vendor-opts option is actually an encapsulated sub-option space,
1315 in which each Vendor-specific Information Option (VSIO) is identified
1316 by a 32-bit Enterprise-ID number. The encapsulated option spaces
1317 within these options are defined by the vendors.
1318 To make use of this option, the best way is to examine the section
1320 titled VENDOR ENCAPSULATED OPTIONS below, in particular the bits
1321 about the "vsio" option space.
1322 option dhcp6.interface-id string;
1324 The interface-id option is manufactured by relay agents, and may be
1326 used to guide configuration differentiating clients by the interface
1327 they are remotely attached to. It does not make sense to configure a
1328 value for this option, but it may make sense to inspect its contents.
1329 option dhcp6.reconf-msg dhcpv6-message;
1331 The reconf-msg option is manufactured by servers, and sent to clients
1333 in Reconfigure messages to inform them of what message the client
1334 should Reconfigure using. There is no support for DHCPv6 Reconfigure
1335 extensions, and this option is documented informationally only.
1336 option dhcp6.reconf-accept ;
1338 The reconf-accept option is included by DHCPv6 clients that support
1340 the Reconfigure extensions, advertising that they will respond if the
1341 server were to ask them to Reconfigure. There is no support for
1342 DHCPv6 Reconfigure extensions, and this option is documented informa‐
1343 tionally only.
1344 option dhcp6.sip-servers-names domain-list;
1346 The sip-servers-names option allows SIP clients to locate a local SIP
1348 server that is to be used for all outbound SIP requests, a so-
1349 called"outbound proxy server." If you wish to use manually entered
1350 IPv6 addresses instead, please see the sip-servers-addresses option
1351 below.
1352 option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;
1354 The sip-servers-addresses option allows SIP clients to locate a local
1356 SIP server that is to be used for all outbound SIP requests, a so-
1357 called "outbound proxy servers." If you wish to use domain names
1358 rather than IPv6 addresses, please see the sip-servers-names option
1359 above.
1360 option dhcp6.name-servers ip6-address [, ip6-address ... ] ;
1362 The name-servers option instructs clients about locally available
1364 recursive DNS servers. It is easiest to describe this as the "name‐
1365 server" line in /etc/resolv.conf.
1366 option dhcp6.domain-search domain-list;
1368 The domain-search option specifies the client's domain search path to
1370 be applied to recursive DNS queries. It is easiest to describe this
1371 as the "search" line in /etc/resolv.conf.
1372 option dhcp6.ia-pd string;
1374 The ia-pd option is manufactured by clients and servers to create a
1376 Prefix Delegation binding - to delegate an IPv6 prefix to the client.
1377 It is not directly edited in dhcpd.conf(5) or dhclient.conf(5), but
1378 rather is manufactured and consumed by the software.
1379 option dhcp6.ia-prefix string;
1381 The ia-prefix option is placed inside ia-pd options in order to iden‐
1383 tify the prefix(es) allocated to the client. It is not directly
1384 edited in dhcpd.conf(5) or dhclient.conf(5), but rather is manufac‐
1385 tured and consumed by the software.
1386 option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;
1388 The nis-servers option identifies, in order, NIS servers available to
1390 the client.
1391 option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;
1393 The nisp-servers option identifies, in order, NIS+ servers available
1395 to the client.
1396 option nis-domain-name domain-list;
1398 The nis-domain-name option specifies the NIS domain name the client
1400 is expected to use, and is related to the nis-servers option.
1401 option dhcp6.nis-domain-name domain-name;
1403 The dhcp6.nis-domain-name option specifies NIS domain name the client
1405 is expected to use, and is related to dhcp6.nis-servers option.
1406 option nisp-domain-name domain-list;
1408 The nisp-domain-name option specifies the NIS+ domain name the client
1410 is expected to use, and is related to the nisp-servers option.
1411 option dhcp6.nisp-domain-name domain-name;
1413 The dhcp6.nis-domain-name option specifies NIS+ domain name the
1415 client is expected to use, and is related to dhcp6.nisp-servers
1416 option.
1417 option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;
1419 The sntp-servers option specifies a list of local SNTP servers avail‐
1421 able for the client to synchronize their clocks.
1422 option dhcp6.info-refresh-time uint32;
1424 The info-refresh-time option gives DHCPv6 clients using Information-
1426 request messages a hint as to how long they should between refreshing
1427 the information they were given. Note that this option will only be
1428 delivered to the client, and be likely to affect the client's behav‐
1429 iour, if the client requested the option.
1430 option dhcp6.bcms-server-d domain-list;
1432 The bcms-server-d option contains the domain names of local BCMS
1434 (Broadcast and Multicast Control Services) controllers which the
1435 client may use.
1436 option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;
1438 The bcms-server-a option contains the IPv6 addresses of local BCMS
1440 (Broadcast and Multicast Control Services) controllers which the
1441 client may use.
1442 option dhcp6.geoconf-civic string;
1444 A string to hold the geoconf civic structure.
1446 This option is included based on RFC 4776.
1448 option dhcp6.remote-id string;
1450 The remote-id option is constructed by relay agents, to inform the
1452 server of details pertaining to what the relay knows about the client
1453 (such as what port it is attached to, and so forth). The contents of
1454 this option have some vendor-specific structure (similar to VSIO),
1455 but we have chosen to treat this option as an opaque field.
1456 option dhcp6.subscriber-id string;
1458 The subscriber-id option is an opaque field provided by the relay
1460 agent, which provides additional information about the subscriber in
1461 question. The exact contents of this option depend upon the vendor
1462 and/or the operator's configuration of the remote device, and as such
1463 is an opaque field.
1464 option dhcp6.fqdn string;
1466 The fqdn option is normally constructed by the client or server, and
1468 negotiates the client's Fully Qualified Domain Name, as well as which
1469 party is responsible for Dynamic DNS Updates. See the section on the
1470 Client FQDN SubOptions for full details (the DHCPv4 and DHCPv6 FQDN
1471 options use the same "fqdn." encapsulated space, so are in all ways
1472 identical).
1473 option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;
1475 A set of IPv6 addresses of a PAA for the client to use. The
1477 addresses are listed in preferred order.
1478 This option is included based on RFC 5192.
1480 option dhcp6.new-posix-timezone text;
1482 This option specifies a string suitable for the TZ variable.
1484 This option is included based on RFC 4833.
1486 option dhcp6.new-tzdb-timezone text;
1488 This option specifies a name of a zone entry in the TZ database.
1490 This option is included based on RFC 4833.
1492 option dhcp6.ero uint16 [, uint16 ... ] ;
1494 A list of the options requested by the relay agent.
1496 This option is included based on RFC 4994.
1498 option dhcp6.lq-query string;
1500 The lq-query option is used internally for lease query.
1502 option dhcp6.client-data string;
1504 The client-data option is used internally for lease query.
1506 option dhcp6.clt-time uint32;
1508 The clt-time option is used internally for lease query.
1510 option dhcp6.lq-relay-data ip6-address string;
1512 The lq-relay-data option is used internally for lease query.
1514 option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;
1516 The lq-client-link option is used internally for lease query.
1518 option dhcp6.v6-lost domain-name;
1520 The domain name of the LoST server for the client to use.
1522 This option is included based on RFC 5223.
1524 option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;
1526 A list of IPv6 addresses of CAPWAP ACs that the WTP may use. The
1528 addresses are listed in preference order.
1529 This option is included based on RFC 5417.
1531 option dhcp6.relay-id string;
1533 The DUID for the relay agent.
1535 This option is included based on RFC 5460.
1537 option dhcp6.v6-access-domain domain-name;
1539 The domain name associated with the access network for use with LIS
1541 Discovery.
1542 This option is included based on RFC5986.
1544 option dhcp6.sip-ua-cs-list domain-list;
1546 The list of domain names in the SIP User Agent Configuration Service
1548 Domains.
1549 This option is included based on RFC 6011.
1551 option dhcp6.bootfile-url text;
1553 The URL for a boot file.
1555 This option is included based on RFC 5970.
1557 option dhcp6.bootfile-param string;
1559 A string for the parameters to the bootfile. See RFC 5970 for more
1561 description of the layout of the parameters within the string.
1562 This option is included based on RFC 5970.
1564 option dhcp6.client-arch-type uint16 [, uint16 ... ] ;
1566 A list of one or more architecture types described as 16 bit values.
1568 This option is included based on RFC 5970.
1570 option dhcp6.nii uint8 uint8 uint8;
1572 The client network interface identitier option supplies information
1574 about a client's level of UNDI support. The values are, in order,
1575 the type, the major value and the minor value.
1576 This option is included based on RFC5970.
1578 option dhcp6.aftr-name domain-name;
1580 A domain name of the AFTR tunnel endpoint.
1582 This option is included based on RFC 6334.
1584 option dhcp6.erp-local-domain-name domain-name;
1586 A domain name for the ERP domain.
1588 This option is included based on RFC 6440.
1590 option dhcp6.rdnss-selection ip6-address uint8 domain-name;
1592 RDNSS information consists of an IPv6 address of RDNSS, an 8 bit
1594 flags field and a domain-list of domains for which the RDNSS has spe‐
1595 cial knowledge.
1596 This option is included based on RFC 6731.
1598 option dhcp6.client-linklayer-addr string;
1600 A client link-layer address. The first two bytes must be the type of
1602 the link-layer followed by the address itself.
1603 This option is included based on RFC 6939.
1605 option dhcp6.link-address ip6-address;
1607 An IPv6 address used by a relay agent to indicate to the server the
1609 link on which the client is located.
1610 This option is included based on RFC 6977.
1612 option dhcp6.solmax-rt uint32;
1614 A value to override the default for SOL_MAX_RT. This is a 32 bit
1616 value.
1617 This option is included based on RFC 7083.
1619 option dhcp6.inf-max-rt uint32;
1621 A value to override the default for INF_MAX_RT. This is a 32 bit
1623 value.
1624 This option is included based on RFC 7083.
1626
1628 v6relay (relay-number, option) This option allows access to an option
1629 that has been added to a packet by a relay agent. Relay-number value
1630 selects the relay to examine and option is the option to find. In
1631 DHCPv6 each relay encapsulates the entire previous message into an
1632 option, adds its own options (if any) and sends the result onwards.
1633 The RFC specifies a limit of 32 hops. A relay-number of 0 is a no-op
1634 and means don't look at the relays. 1 is the relay that is closest to
1635 the client, 2 would be the next in from the client and so on. Any
1636 value greater than the max number of hops is which is closest to the
1637 server independent of number. To use this option in a class statement
1638 you would have something like this:
1639 match if v6relay(1, option dhcp6.subscriber-id) = "client_1";
1641
1643 The Internet Systems Consortium DHCP client and server provide the
1644 capability to define new options. Each DHCP option has a name, a code,
1645 and a structure. The name is used by you to refer to the option. The
1646 code is a number, used by the DHCP server and client to refer to an
1647 option. The structure describes what the contents of an option looks
1648 like.
1649 To define a new option, you need to choose a name for it that is not in
1651 use for some other option - for example, you can't use "host-name"
1652 because the DHCP protocol already defines a host-name option, which is
1653 documented earlier in this manual page. If an option name doesn't
1654 appear in this manual page, you can use it, but it's probably a good
1655 idea to put some kind of unique string at the beginning so you can be
1656 sure that future options don't take your name. For example, you might
1657 define an option, "local-host-name", feeling some confidence that no
1658 official DHCP option name will ever start with "local".
1659 Once you have chosen a name, you must choose a code. All codes between
1661 224 and 254 are reserved as ´site-local´ DHCP options, so you can pick
1662 any one of these for your site (not for your product/application). In
1663 RFC3942, site-local space was moved from starting at 128 to starting at
1664 224. In practice, some vendors have interpreted the protocol rather
1665 loosely and have used option code values greater than 128 themselves.
1666 There's no real way to avoid this problem, and it was thought to be
1667 unlikely to cause too much trouble in practice. If you come across a
1668 vendor-documented option code in either the new or old site-local spa‐
1669 ces, please contact your vendor and inform them about rfc3942.
1670 The structure of an option is simply the format in which the option
1672 data appears. The ISC DHCP server currently supports a few simple
1673 types, like integers, booleans, strings and IP addresses, and it also
1674 supports the ability to define arrays of single types or arrays of
1675 fixed sequences of types.
1676 New options are declared as follows:
1678 option new-name code new-code = definition ;
1680 The values of new-name and new-code should be the name you have chosen
1682 for the new option and the code you have chosen. The definition should
1683 be the definition of the structure of the option.
1684 The following simple option type definitions are supported:
1686 BOOLEAN
1688 option new-name code new-code = boolean ;
1690 An option of type boolean is a flag with a value of either on or off
1692 (or true or false). So an example use of the boolean type would be:
1693 option use-zephyr code 180 = boolean;
1695 option use-zephyr on;
1696 INTEGER
1698 option new-name code new-code = sign integer width ;
1700 The sign token should either be blank, unsigned or signed. The width
1702 can be either 8, 16 or 32, and refers to the number of bits in the
1703 integer. So for example, the following two lines show a definition of
1704 the sql-connection-max option and its use:
1705 option sql-connection-max code 192 = unsigned integer 16;
1707 option sql-connection-max 1536;
1708 IP-ADDRESS
1710 option new-name code new-code = ip-address ;
1712 An option whose structure is an IP address can be expressed either as a
1714 domain name or as a dotted quad. So the following is an example use of
1715 the ip-address type:
1716 option sql-server-address code 193 = ip-address;
1718 option sql-server-address sql.example.com;
1719 IP6-ADDRESS
1721 option new-name code new-code = ip6-address ;
1723 An option whose structure is an IPv6 address must be expressed as a
1725 valid IPv6 address. The following is an example use of the ip6-address
1726 type:
1727 option dhcp6.some-server code 1234 = array of ip6-address;
1729 option dhcp6.some-server 3ffe:bbbb:aaaa:aaaa::1, 3ffe:bbbb:aaaa:aaaa::2;
1730 TEXT
1733 option new-name code new-code = text ;
1735 An option whose type is text will encode an ASCII text string. For
1737 example:
1738 option sql-default-connection-name code 194 = text;
1740 option sql-default-connection-name "PRODZA";
1741 DATA STRING
1744 option new-name code new-code = string ;
1746 An option whose type is a data string is essentially just a collection
1748 of bytes, and can be specified either as quoted text, like the text
1749 type, or as a list of hexadecimal contents separated by colons whose
1750 values must be between 0 and FF. For example:
1751 option sql-identification-token code 195 = string;
1753 option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;
1754 DOMAIN-LIST
1757 option new-name code new-code = domain-list [compressed] ;
1759 An option whose type is domain-list is an RFC1035 formatted (on the
1761 wire, "DNS Format") list of domain names, separated by root labels.
1762 The optional compressed keyword indicates if the option should be com‐
1763 pressed relative to the start of the option contents (not the packet
1764 contents).
1765 When in doubt, omit the compressed keyword. When the software receives
1767 an option that is compressed and the compressed keyword is omitted, it
1768 will still decompress the option (relative to the option contents
1769 field). The keyword only controls whether or not transmitted packets
1770 are compressed.
1771 Note that when domain-list formatted options are output as environment
1773 variables to dhclient-script(8), the standard DNS -escape mechanism is
1774 used: they are decimal. This is appropriate for direct use in eg
1775 /etc/resolv.conf.
1776 ENCAPSULATION
1779 option new-name code new-code = encapsulate identifier ;
1781 An option whose type is encapsulate will encapsulate the contents of
1783 the option space specified in identifier. Examples of encapsulated
1784 options in the DHCP protocol as it currently exists include the vendor-
1785 encapsulated-options option, the netware-suboptions option and the
1786 relay-agent-information option.
1787 option space local;
1789 option local.demo code 1 = text;
1790 option local-encapsulation code 197 = encapsulate local;
1791 option local.demo "demo";
1792 ARRAYS
1795 Options can contain arrays of any of the above types except for the
1797 text and data string types, which aren't currently supported in arrays.
1798 An example of an array definition is as follows:
1799 option kerberos-servers code 200 = array of ip-address;
1801 option kerberos-servers 10.20.10.1, 10.20.11.1;
1802 RECORDS
1804 Options can also contain data structures consisting of a sequence of
1806 data types, which is sometimes called a record type. For example:
1807 option contrived-001 code 201 = { boolean, integer 32, text };
1809 option contrived-001 on 1772 "contrivance";
1810 It's also possible to have options that are arrays of records, for
1812 example:
1813 option new-static-routes code 201 = array of {
1815 ip-address, ip-address, ip-address, integer 8 };
1816 option static-routes
1817 10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
1818 10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
1819 10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;
1820
1823 The DHCP protocol defines the vendor-encapsulated-options option, which
1824 allows vendors to define their own options that will be sent encapsu‐
1825 lated in a standard DHCP option. It also defines the Vendor Identified
1826 Vendor Sub Options option ("VIVSO"), and the DHCPv6 protocol defines
1827 the Vendor-specific Information Option ("VSIO"). The format of all of
1828 these options is usually internally a string of options, similarly to
1829 other normal DHCP options. The VIVSO and VSIO options differ in that
1830 they contain options that correspond to vendor Enterprise-ID numbers
1831 (assigned by IANA), which then contain options according to each Ven‐
1832 dor's specifications. You will need to refer to your vendor's documen‐
1833 tation in order to form options to their specification.
1834 The value of these options can be set in one of two ways. The first
1836 way is to simply specify the data directly, using a text string or a
1837 colon-separated list of hexadecimal values. For help in forming these
1838 strings, please refer to RFC2132 for the DHCPv4 Vendor Specific Infor‐
1839 mation Option, RFC3925 for the DHCPv4 Vendor Identified Vendor Sub
1840 Options, or RFC3315 for the DHCPv6 Vendor-specific Information Option.
1841 For example:
1842 option vendor-encapsulated-options
1844 2:4:
1845 AC:11:41:1:
1846 3:12:
1847 73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
1848 4:12:
1849 2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
1850 option vivso
1851 00:00:09:bf:0E:
1852 01:0c:
1853 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1854 option dhcp6.vendor-opts
1855 00:00:09:bf:
1856 00:01:00:0c:
1857 48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1858 The second way of setting the value of these options is to have the
1860 DHCP server generate a vendor-specific option buffer. To do this, you
1861 must do four things: define an option space, define some options in
1862 that option space, provide values for them, and specify that that
1863 option space should be used to generate the relevant option.
1864 To define a new option space in which vendor options can be stored, use
1866 the option space statement:
1867 option space name [ [ code width number ] [ length width number ] [
1869 hash size number ] ] ;
1870 Where the numbers following code width, length width, and hash size
1872 respectively identify the number of bytes used to describe option
1873 codes, option lengths, and the size in buckets of the hash tables to
1874 hold options in this space (most DHCPv4 option spaces use 1 byte codes
1875 and lengths, which is the default, whereas most DHCPv6 option spaces
1876 use 2 byte codes and lengths).
1877 The code and length widths are used in DHCP protocol - you must config‐
1879 ure these numbers to match the applicable option space you are config‐
1880 uring. They each default to 1. Valid values for code widths are 1, 2
1881 or 4. Valid values for length widths are 0, 1 or 2. Most DHCPv4
1882 option spaces use 1 byte codes and lengths, which is the default,
1883 whereas most DHCPv6 option spaces use 2 byte codes and lengths. A
1884 zero-byte length produces options similar to the DHCPv6 Vendor-specific
1885 Information Option - but not their contents!
1886 The hash size defaults depend upon the code width selected, and may be
1888 254 or 1009. Valid values range between 1 and 65535. Note that the
1889 higher you configure this value, the more memory will be used. It is
1890 considered good practice to configure a value that is slightly larger
1891 than the estimated number of options you plan to configure within the
1892 space. Previous versions of ISC DHCP (up to and including DHCP 3.0.*),
1893 this value was fixed at 9973.
1894 The name can then be used in option definitions, as described earlier
1896 in this document. For example:
1897 option space SUNW code width 1 length width 1 hash size 3;
1899 option SUNW.server-address code 2 = ip-address;
1900 option SUNW.server-name code 3 = text;
1901 option SUNW.root-path code 4 = text;
1902 option space ISC code width 1 length width 1 hash size 3;
1904 option ISC.sample code 1 = text;
1905 option vendor.ISC code 2495 = encapsulate vivso-sample;
1906 option vendor-class.ISC code 2495 = text;
1907 option ISC.sample "configuration text here";
1909 option vendor-class.ISC "vendor class here";
1910 option space docsis code width 2 length width 2 hash size 17;
1912 option docsis.tftp-servers code 32 = array of ip6-address;
1913 option docsis.cablelabs-configuration-file code 33 = text;
1914 option docsis.cablelabs-syslog-servers code 34 = array of ip6-address;
1915 option docsis.device-id code 36 = string;
1916 option docsis.time-servers code 37 = array of ip6-address;
1917 option docsis.time-offset code 38 = signed integer 32;
1918 option vsio.docsis code 4491 = encapsulate docsis;
1919 Once you have defined an option space and the format of some options,
1921 you can set up scopes that define values for those options, and you can
1922 say when to use them. For example, suppose you want to handle two dif‐
1923 ferent classes of clients. Using the option space definition shown in
1924 the previous example, you can send different option values to different
1925 clients based on the vendor-class-identifier option that the clients
1926 send, as follows:
1927 class "vendor-classes" {
1929 match option vendor-class-identifier;
1930 }
1931 subclass "vendor-classes" "SUNW.Ultra-5_10" {
1933 vendor-option-space SUNW;
1934 option SUNW.root-path "/export/root/sparc";
1935 }
1936 subclass "vendor-classes" "SUNW.i86pc" {
1938 vendor-option-space SUNW;
1939 option SUNW.root-path "/export/root/i86pc";
1940 }
1941 option SUNW.server-address 172.17.65.1;
1943 option SUNW.server-name "sundhcp-server17-1";
1944 option vivso-sample.sample "Hello world!";
1946 option docsis.tftp-servers ::1;
1948 As you can see in the preceding example, regular scoping rules apply,
1951 so you can define values that are global in the global scope, and only
1952 define values that are specific to a particular class in the local
1953 scope. The vendor-option-space declaration tells the DHCP server to
1954 use options in the SUNW option space to construct the DHCPv4 vendor-
1955 encapsulated-options option. This is a limitation of that option - the
1956 DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi‐
1957 nitions all at once (even transmitted to the same client), so it is not
1958 necessary to configure this.
1959
1961 dhcpd.conf(5), dhcpd.leases(5), dhclient.conf(5), dhcp-eval(5),
1962 dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.
1963
1965 Information about Internet Systems Consortium can be found at
1966 https://www.isc.org.
1967 dhcp-options(5)