1dhcp-options(5)               File Formats Manual              dhcp-options(5)
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3
4

NAME

6       dhcp-options - Dynamic Host Configuration Protocol options
7

DESCRIPTION

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

REFERENCE: OPTION STATEMENTS

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
23       Option data comes in a variety of formats, as defined below:
24
25       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
36       The   ip6-address   data   specifies  an  IPv6  address,  like  ::1  or
37       3ffe:bbbb:aaaa:aaaa::1.
38
39       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
45       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
49       option root-path "10.0.1.4:/var/tmp/rootfs";
50
51       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
55       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
59       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
62       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
66         option dhcp-client-identifier "CLIENT-FOO";
67       or
68         option dhcp-client-identifier 43:4c:49:45:54:2d:46:4f:4f;
69
70       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
77       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

SETTING OPTION VALUES USING EXPRESSIONS

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
93         option my-option = expression ;
94
95       For example:
96
97         option hostname = binary-to-ascii (16, 8, "-",
98                                            substring (hardware, 1, 6));
99

INCLUDING OPTION DEFINITIONS

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
108       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

STANDARD DHCPV4 OPTIONS

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
119       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
129       The standard options are:
130
131       option all-subnets-local flag;
132
133         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
141       option arp-cache-timeout uint32;
142
143         This option specifies the timeout in seconds for ARP cache entries.
144
145       option associated-ip ip-address [, ip-address... ];
146
147         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
150         This option is not user configurable.
151
152       option bcms-controller-address ip-address [, ip-address... ];
153
154         This option configures a list of IPv4 addresses for use as  Broadcast
155         and Multicast Controller Servers ("BCMS").
156
157       option bcms-controller-names domain-list;
158
159         This  option  contains the domain names of local Broadcast and Multi‐
160         cast Controller Servers ("BCMS") controllers  which  the  client  may
161         use.
162
163       option bootfile-name text;
164
165         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
170       option boot-size uint16;
171
172         This option specifies the length in 512-octet blocks of  the  default
173         boot image for the client.
174
175       option broadcast-address ip-address;
176
177         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
181       option capwap-ac-v4 ip-address [, ip-address ... ] ;
182
183         A list of IPv4 addresses of CAPWAP ACs that the WTP may use.  The ad‐
184         dresses are listed in preference order.
185
186         This option is included based on RFC 5417.
187
188       option client-last-transaction-time uint32;
189
190         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
195         This option is not user configurable.
196
197       option cookie-servers ip-address [, ip-address...  ];
198
199         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
203       option default-ip-ttl uint8;
204
205         This option specifies the default time-to-live that the client should
206         use on outgoing datagrams.
207
208       option default-tcp-ttl uint8;
209
210         This option specifies the default TTL that the client should use when
211         sending TCP segments.  The minimum value is 1.
212
213       option default-url string;
214
215         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
220       option dhcp-client-identifier string;
221
222         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
226         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
230              option dhcp-client-identifier "\0foo";
231
232         rather than:
233
234              option dhcp-client-identifier "foo";
235
236       option dhcp-lease-time uint32;
237
238         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
243         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
247       option dhcp-max-message-size uint16;
248
249         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
255       option dhcp-message text;
256
257         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
262         This option is not user configurable.
263
264       option dhcp-message-type uint8;
265
266         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
270                      1     DHCPDISCOVER
271                      2     DHCPOFFER
272                      3     DHCPREQUEST
273                      4     DHCPDECLINE
274                      5     DHCPACK
275                      6     DHCPNAK
276                      7     DHCPRELEASE
277                      8     DHCPINFORM
278
279         This option is not user configurable.
280
281       option dhcp-option-overload uint8;
282
283         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
288         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
292         Legal values for this option are:
293
294                      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
298         This option is not user configurable.
299
300       option dhcp-parameter-request-list uint8 [, uint8... ];
301
302         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
313       option dhcp-rebinding-time uint32;
314
315         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
318         This option is user configurable, but it will be ignored if the value
319         is greater than or equal to the lease time.
320
321         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
324       option dhcp-renewal-time uint32;
325
326         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
329         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
332         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
335       option dhcp-requested-address ip-address;
336
337         This option is used by the client in a DHCPDISCOVER to request that a
338         particular IP address be assigned.
339
340         This option is not user configurable.
341
342       option dhcp-server-identifier ip-address;
343
344         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
353         The value of this option is the IP address of the server.
354
355         This option is not directly user configurable. See the server-identi‐
356         fier server option in dhcpd.conf(5).
357
358       option domain-name text;
359
360         This option specifies the domain name that client should use when re‐
361         solving hostnames via the Domain Name System.
362
363       option domain-name-servers ip-address [, ip-address...  ];
364
365         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
369       option domain-search domain-list;
370
371         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
377           option domain-search "example.com", "sales.example.com",
378                                "eng.example.com";
379
380       option extensions-path text;
381
382         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
386       option finger-server ip-address [, ip-address... ];
387
388         The Finger server option specifies a list of Finger servers available
389         to the client.  Servers should be listed in order of preference.
390
391       option font-servers ip-address [, ip-address...  ];
392
393         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
396       option geoconf-civic string;
397
398         A string to hold the geoconf civic structure.
399
400         This option is included based on RFC 4776.
401
402       option host-name string;
403
404         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
410       option ieee802-3-encapsulation flag;
411
412         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
418       option ien116-name-servers ip-address [, ip-address...  ];
419
420         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
424       option impress-servers ip-address [, ip-address...  ];
425
426         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
430       option interface-mtu uint16;
431
432         This option specifies the MTU to use on this interface.  The  minimum
433         legal value for the MTU is 68.
434
435       option ip-forwarding flag;
436
437         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
441       option irc-server ip-address [, ip-address... ];
442
443         The  IRC  server  option specifies a list of IRC servers available to
444         the client.  Servers should be listed in order of preference.
445
446
447       option loader-configfile text
448
449         This option is used to specify a boot loading  configuration  file  a
450         PXE client should use.
451
452         This option is included based on RFC 5071.
453
454       option loader-pathprefix text
455
456         This  option is used to specify a path prefix a PXE client should use
457         in conjunction with the boot load configuration file.
458
459         This option is included based on RFC 5071.
460
461       option loader-reboottime uint32
462
463         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
467         This option is included based on RFC 5071.
468
469       option log-servers ip-address [, ip-address...  ];
470
471         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
475       option lpr-servers ip-address  [, ip-address...  ];
476
477         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
481       option mask-supplier flag;
482
483         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
488       option max-dgram-reassembly uint16;
489
490         This  option  specifies  the  maximum  size  datagram that the client
491         should be prepared to reassemble.  The minimum legal value is 576.
492
493       option merit-dump text;
494
495         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
500       option mobile-ip-home-agent ip-address [, ip-address... ];
501
502         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
507       option name-service-search uint16 [, uint6... ];
508
509         This option specifies a list of name services in the order the client
510         should attempt to use them.
511
512         This option is included based on RFC 2937.
513
514       option nds-context string;
515
516         The  nds-context option specifies the name of the initial Netware Di‐
517         rectory Service for an NDS client.
518
519       option nds-servers ip-address [, ip-address... ];
520
521         The nds-servers option specifies  a  list  of  IP  addresses  of  NDS
522         servers.
523
524       option nds-tree-name string;
525
526         The  nds-tree-name option specifies NDS tree name that the NDS client
527         should use.
528
529       option netbios-dd-server ip-address [, ip-address...  ];
530
531         The NetBIOS datagram distribution server (NBDD)  option  specifies  a
532         list of RFC 1001/1002 NBDD servers listed in order of preference.
533
534       option netbios-name-servers ip-address [, ip-address...];
535
536         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
541       option netbios-node-type uint8;
542
543         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
548         Possible node types are:
549
550         1    B-node: Broadcast - no WINS
551
552         2    P-node: Peer - WINS only
553
554         4    M-node: Mixed - broadcast, then WINS
555
556         8    H-node: Hybrid - WINS, then broadcast
557
558       option netbios-scope string;
559
560         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
564       option netinfo-server-address ip-address [, ip-address... ];
565
566         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
572       option netinfo-server-tag text;
573
574         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
580       option nis-domain text;
581
582         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
586       option nis-servers ip-address [, ip-address...  ];
587
588         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
592       option nisplus-domain text;
593
594         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
598       option nisplus-servers ip-address [, ip-address...  ];
599
600         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
604       option nntp-server ip-address [, ip-address... ];
605
606         The  NNTP server option specifies a list of NNTP servers available to
607         the client.  Servers should be listed in order of preference.
608
609       option non-local-source-routing flag;
610
611         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
617       option ntp-servers ip-address [, ip-address...  ];
618
619         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
623       option nwip-domain string;
624
625         The name of the NetWare/IP domain that  a  NetWare/IP  client  should
626         use.
627
628       option nwip-suboptions string;
629
630         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
635       option pxe-system-type uint16 [, uint16 ... ];
636
637         A list of one ore more 16-bit integers which allows a client to spec‐
638         ify its pre-boot architecture type(s).
639
640         This option is included based on RFC 4578.
641
642       option pxe-interface-id uint8 uint8 uint8
643
644         A  three octet value which allows a client to specify its network in‐
645         terface type.
646
647         This option is included based on RFC 4578.
648
649       option pxe-client-id uint8 string
650
651         A single octet indicating type, followed by a string  that  allows  a
652         client to specify its PXE client identity.
653
654         This option is included based on RFC 4578.
655
656       option  option-6rd  uint8  uint8  ip6-address  ip-address [, ip-address
657       ...];
658
659         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
664         This option is included based on RFC 5969.
665
666       option pana-agent ip-address [, ip-address ... ] ;
667
668         A  set  of  IPv4  addresses  of a PAA for the client to use.  The ad‐
669         dresses are listed in preferred order.
670
671         This option is included based on RFC 5192.
672
673       option path-mtu-aging-timeout uint32;
674
675         This option specifies the timeout (in seconds) to use when aging Path
676         MTU values discovered by the mechanism defined in RFC 1191.
677
678       option path-mtu-plateau-table uint16 [, uint16...  ];
679
680         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
685       option pcode text;
686
687         This option specifies a string suitable for the TZ variable.
688
689         This option is included based on RFC 4833.
690
691       option perform-mask-discovery flag;
692
693         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
698       option policy-filter ip-address ip-address
699                         [, ip-address ip-address...];
700
701         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
705         Any  source routed datagram whose next-hop address does not match one
706         of the filters should be discarded by the client.
707
708         See STD 3 (RFC1122) for further information.
709
710       option pop-server ip-address [, ip-address... ];
711
712         The POP3 server option specifies a list of POP3 servers available  to
713         the client.  Servers should be listed in order of preference.
714
715       option rdnss-selection uint8 ip-address ip-address domain-name;
716
717         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
721         This option is included based on RFC 6731.
722
723       option resource-location-servers ip-address
724                                     [, ip-address...];
725
726         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
730       option root-path text;
731
732         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
736       option router-discovery flag;
737
738         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
744       option router-solicitation-address ip-address;
745
746         This option specifies the address to which the client should transmit
747         router solicitation requests.
748
749       option routers ip-address [, ip-address...  ];
750
751         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
755       option slp-directory-agent boolean ip-address [, ip-address... ];
756
757         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
764         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
769         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
773       option slp-service-scope boolean text;
774
775         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
782         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
787       option smtp-server ip-address [, ip-address... ];
788
789         The SMTP server option specifies a list of SMTP servers available  to
790         the client.  Servers should be listed in order of preference.
791
792       option static-routes ip-address ip-address
793                         [, ip-address ip-address...];
794
795         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
800         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
804         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
812         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
822       option classless-static-routes destination-descriptor ip-address
823                                   [, destination-descriptor ip-address...];
824
825         This option (see RFC3442) specifies a list of classless static routes
826         that the client should install in its routing cache.
827
828         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
832         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
838         If  the DHCP server returns both a Classless Static Routes option and
839         a Router option, the DHCP client ignores the Router option.
840
841       option streettalk-directory-assistance-server ip-address
842                                                  [, ip-address...];
843
844         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
848       option streettalk-server ip-address [, ip-address... ];
849
850         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
854       option subnet-mask ip-address;
855
856         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
864       option subnet-selection ip-address;
865
866         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
874       This option is not user configurable in the server.
875
876       option swap-server ip-address;
877
878         This specifies the IP address of the client's swap server.
879
880       option tftp-server-address ip-address [, ip-address... ];
881
882         This option configures a list of one or more IPv4 addresses  of  tftp
883         servers a client may use.
884
885         This option is included based on RFC 5859
886
887       option tcp-keepalive-garbage flag;
888
889         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
895       option tcp-keepalive-interval uint32;
896
897         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
903       option tcode text;
904
905         This option specifies a name of a zone entry in the TZ database.
906
907         This option is included based on RFC 4833.
908
909       option tftp-server-name text;
910
911         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
916       option time-offset int32;
917
918         The time-offset option specifies the offset of the client's subnet in
919         seconds from Coordinated Universal Time (UTC).
920
921       option time-servers ip-address [, ip-address...  ];
922
923         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
927       option trailer-encapsulation flag;
928
929         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
935       option uap-servers text;
936
937         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
947       option user-class string;
948
949         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
956       option v4-access-domain domain-name;
957
958         The domain name associated with the access network for use  with  LIS
959         Discovery.
960
961         This option is included based on RFC 5986.
962
963       option v4-lost domain-name;
964
965         The domain name of the LoST server for the client to use.
966
967         This option is included based on RFC 5223.
968
969       option v6-only-preferred uint32;
970
971         The number of seconds the client should disable DHCPv4 for.
972
973         This option and its use by the client are specified in RFC 8925.
974
975       option vendor-class-identifier string;
976
977         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
984         set vendor-string = option vendor-class-identifier;
985
986         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
990         set vendor-string = "SUNW.Ultra-5_10";
991
992         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
997       option vendor-encapsulated-options string;
998
999         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
1006         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
1012       option vivso string;
1013
1014         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
1022       option www-server ip-address [, ip-address... ];
1023
1024         The WWW server option specifies a list of WWW  servers  available  to
1025         the client.  Servers should be listed in order of preference.
1026
1027       option x-display-manager ip-address [, ip-address...  ];
1028
1029         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

RELAY AGENT INFORMATION OPTION

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
1042       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
1048       option agent.circuit-id string;
1049
1050         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
1058       option agent.remote-id string;
1059
1060         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
1068       option agent.DOCSIS-device-class uint32;
1069
1070         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
1080       option agent.link-selection ip-address;
1081
1082         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

THE CLIENT FQDN SUBOPTIONS

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
1101       option fqdn.no-client-update flag;
1102
1103         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
1107       option fqdn.server-update flag;
1108
1109         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
1113       option fqdn.encoded flag;
1114
1115         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
1123       option fqdn.rcode1 flag;
1124
1125       option fqdn.rcode2 flag;
1126
1127         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
1132       option fqdn.fqdn text;
1133
1134         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
1140       option fqdn.hostname --never set--;
1141
1142         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
1148       option fqdn.domainname --never set--;
1149
1150         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
1158       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

THE NETWARE/IP SUBOPTIONS

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
1170       option nwip.nsq-broadcast flag;
1171
1172         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
1176       option nwip.preferred-dss ip-address [, ip-address... ];
1177
1178         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
1182       option nwip.nearest-nwip-server ip-address
1183                                    [, ip-address...];
1184
1185         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
1188       option nwip.autoretries uint8;
1189
1190         Specifies the number of times that a NetWare/IP client should attempt
1191         to communicate with a given DSS server at startup.
1192
1193       option nwip.autoretry-secs uint8;
1194
1195         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
1199       option nwip.nwip-1-1 uint8;
1200
1201         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
1205       option nwip.primary-dss ip-address;
1206
1207         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

STANDARD DHCPV6 OPTIONS

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
1222       option dhcp6.client-id string;
1223
1224         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
1228         duid-llt
1229
1230         duid-en
1231
1232         duid-ll
1233
1234         This  value  should  not  be  configured,  but  rather is provided by
1235         clients and treated as an opaque identifier key blob by servers.
1236
1237       option dhcp6.server-id string;
1238
1239         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
1243       option dhcp6.ia-na string;
1244
1245         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
1250       option dhcp6.ia-ta string;
1251
1252         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
1256       option dhcp6.ia-addr string;
1257
1258         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
1263       option dhcp6.oro uint16 [ , uint16, ... ];
1264
1265         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
1271       option dhcp6.preference uint8;
1272
1273         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
1280       option dhcp6.elapsed-time uint16;
1281
1282         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
1286       option dhcp6.relay-msg string;
1287
1288         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
1292       option dhcp6.unicast ip6-address;
1293
1294         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
1305       option dhcp6.status-code status-code [ string ] ;
1306
1307         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
1312       option dhcp6.rapid-commit ;
1313
1314         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
1317       option dhcp6.vendor-opts string;
1318
1319         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
1324         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
1328       option dhcp6.interface-id string;
1329
1330         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
1335       option dhcp6.reconf-msg dhcpv6-message;
1336
1337         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
1342       option dhcp6.reconf-accept ;
1343
1344         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
1350       option dhcp6.sip-servers-names domain-list;
1351
1352         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
1358       option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;
1359
1360         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
1366       option dhcp6.name-servers ip6-address [, ip6-address ... ] ;
1367
1368         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
1372       option dhcp6.domain-search domain-list;
1373
1374         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
1378       option dhcp6.ia-pd string;
1379
1380         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
1385       option dhcp6.ia-prefix string;
1386
1387         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
1392       option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;
1393
1394         The nis-servers option identifies, in order, NIS servers available to
1395         the client.
1396
1397       option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;
1398
1399         The nisp-servers option identifies, in order, NIS+ servers  available
1400         to the client.
1401
1402       option nis-domain-name domain-list;
1403
1404         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
1407       option dhcp6.nis-domain-name domain-name;
1408
1409         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
1412       option nisp-domain-name domain-list;
1413
1414         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
1417       option dhcp6.nisp-domain-name domain-name;
1418
1419         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
1423       option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;
1424
1425         The sntp-servers option specifies a list of local SNTP servers avail‐
1426         able for the client to synchronize their clocks.
1427
1428       option dhcp6.info-refresh-time uint32;
1429
1430         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
1436       option dhcp6.bcms-server-d domain-list;
1437
1438         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
1442       option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;
1443
1444         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
1448       option dhcp6.geoconf-civic string;
1449
1450         A string to hold the geoconf civic structure.
1451
1452         This option is included based on RFC 4776.
1453
1454       option dhcp6.remote-id string;
1455
1456         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
1462       option dhcp6.subscriber-id string;
1463
1464         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
1470       option dhcp6.fqdn string;
1471
1472         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
1479       option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;
1480
1481         A set of IPv6 addresses of a PAA for the  client  to  use.   The  ad‐
1482         dresses are listed in preferred order.
1483
1484         This option is included based on RFC 5192.
1485
1486       option dhcp6.new-posix-timezone text;
1487
1488         This option specifies a string suitable for the TZ variable.
1489
1490         This option is included based on RFC 4833.
1491
1492       option dhcp6.new-tzdb-timezone text;
1493
1494         This option specifies a name of a zone entry in the TZ database.
1495
1496         This option is included based on RFC 4833.
1497
1498       option dhcp6.ero uint16 [, uint16 ... ] ;
1499
1500         A list of the options requested by the relay agent.
1501
1502         This option is included based on RFC 4994.
1503
1504       option dhcp6.lq-query string;
1505
1506         The lq-query option is used internally for lease query.
1507
1508       option dhcp6.client-data string;
1509
1510         The client-data option is used internally for lease query.
1511
1512       option dhcp6.clt-time uint32;
1513
1514         The clt-time option is used internally for lease query.
1515
1516       option dhcp6.lq-relay-data ip6-address string;
1517
1518         The lq-relay-data option is used internally for lease query.
1519
1520       option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;
1521
1522         The lq-client-link option is used internally for lease query.
1523
1524       option dhcp6.v6-lost domain-name;
1525
1526         The domain name of the LoST server for the client to use.
1527
1528         This option is included based on RFC 5223.
1529
1530       option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;
1531
1532         A list of IPv6 addresses of CAPWAP ACs that the WTP may use.  The ad‐
1533         dresses are listed in preference order.
1534
1535         This option is included based on RFC 5417.
1536
1537       option dhcp6.relay-id string;
1538
1539         The DUID for the relay agent.
1540
1541         This option is included based on RFC 5460.
1542
1543       option dhcp6.v6-access-domain domain-name;
1544
1545         The domain name associated with the access network for use  with  LIS
1546         Discovery.
1547
1548         This option is included based on RFC5986.
1549
1550       option dhcp6.sip-ua-cs-list domain-list;
1551
1552         The  list of domain names in the SIP User Agent Configuration Service
1553         Domains.
1554
1555         This option is included based on RFC 6011.
1556
1557       option dhcp6.bootfile-url text;
1558
1559         The URL for a boot file.
1560
1561         This option is included based on RFC 5970.
1562
1563       option dhcp6.bootfile-param string;
1564
1565         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
1568         This option is included based on RFC 5970.
1569
1570       option dhcp6.client-arch-type uint16 [, uint16 ... ] ;
1571
1572         A list of one or more architecture types described as 16 bit values.
1573
1574         This option is included based on RFC 5970.
1575
1576       option dhcp6.nii uint8 uint8 uint8;
1577
1578         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
1582         This option is included based on RFC5970.
1583
1584       option dhcp6.aftr-name domain-name;
1585
1586         A domain name of the AFTR tunnel endpoint.
1587
1588         This option is included based on RFC 6334.
1589
1590       option dhcp6.erp-local-domain-name domain-name;
1591
1592         A domain name for the ERP domain.
1593
1594         This option is included based on RFC 6440.
1595
1596       option dhcp6.rdnss-selection ip6-address uint8 domain-name;
1597
1598         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
1602         This option is included based on RFC 6731.
1603
1604       option dhcp6.client-linklayer-addr string;
1605
1606         A client link-layer address.  The first two bytes must be the type of
1607         the link-layer followed by the address itself.
1608
1609         This option is included based on RFC 6939.
1610
1611       option dhcp6.link-address ip6-address;
1612
1613         An IPv6 address used by a relay agent to indicate to the  server  the
1614         link on which the client is located.
1615
1616         This option is included based on RFC 6977.
1617
1618       option dhcp6.solmax-rt uint32;
1619
1620         A  value  to  override  the default for SOL_MAX_RT.  This is a 32 bit
1621         value.
1622
1623         This option is included based on RFC 7083.
1624
1625       option dhcp6.inf-max-rt uint32;
1626
1627         A value to override the default for INF_MAX_RT.  This  is  a  32  bit
1628         value.
1629
1630         This option is included based on RFC 7083.
1631

ACCESSING DHCPV6 RELAY OPTIONS

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
1645       match if v6relay(1, option dhcp6.subscriber-id) = "client_1";
1646

DEFINING NEW OPTIONS

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
1655       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
1665       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
1676       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
1682       New options are declared as follows:
1683
1684       option new-name code new-code = definition ;
1685
1686       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
1690       The following simple option type definitions are supported:
1691
1692       BOOLEAN
1693
1694       option new-name code new-code = boolean ;
1695
1696       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
1699       option use-zephyr code 180 = boolean;
1700       option use-zephyr on;
1701
1702       INTEGER
1703
1704       option new-name code new-code = sign integer width ;
1705
1706       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
1711       option sql-connection-max code 192 = unsigned integer 16;
1712       option sql-connection-max 1536;
1713
1714       IP-ADDRESS
1715
1716       option new-name code new-code = ip-address ;
1717
1718       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
1722       option sql-server-address code 193 = ip-address;
1723       option sql-server-address sql.example.com;
1724
1725       IP6-ADDRESS
1726
1727       option new-name code new-code = ip6-address ;
1728
1729       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
1733       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
1736
1737       TEXT
1738
1739       option new-name code new-code = text ;
1740
1741       An option whose type is text will encode an ASCII text string.  For ex‐
1742       ample:
1743
1744       option sql-default-connection-name code 194 = text;
1745       option sql-default-connection-name "PRODZA";
1746
1747
1748       DATA STRING
1749
1750       option new-name code new-code = string ;
1751
1752       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
1757       option sql-identification-token code 195 = string;
1758       option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;
1759
1760
1761       DOMAIN-LIST
1762
1763       option new-name code new-code = domain-list [compressed] ;
1764
1765       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
1771       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
1777       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
1782
1783       ENCAPSULATION
1784
1785       option new-name code new-code = encapsulate identifier ;
1786
1787       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
1793       option space local;
1794       option local.demo code 1 = text;
1795       option local-encapsulation code 197 = encapsulate local;
1796       option local.demo "demo";
1797
1798
1799       ARRAYS
1800
1801       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
1805       option kerberos-servers code 200 = array of ip-address;
1806       option kerberos-servers 10.20.10.1, 10.20.11.1;
1807
1808       RECORDS
1809
1810       Options can also contain data structures consisting of  a  sequence  of
1811       data types, which is sometimes called a record type.  For example:
1812
1813       option contrived-001 code 201 = { boolean, integer 32, text };
1814       option contrived-001 on 1772 "contrivance";
1815
1816       It's  also possible to have options that are arrays of records, for ex‐
1817       ample:
1818
1819       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
1826

VENDOR ENCAPSULATED OPTIONS

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
1840       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
1848       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
1864       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
1870       To define a new option space in which vendor options can be stored, use
1871       the option space statement:
1872
1873       option  space  name  [  [ code width number ] [ length width number ] [
1874       hash size number ] ] ;
1875
1876       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
1883       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
1892       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
1900       The name can then be used in option definitions, as  described  earlier
1901       in this document.  For example:
1902
1903       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
1908       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
1913       option ISC.sample "configuration text here";
1914       option vendor-class.ISC "vendor class here";
1915
1916       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
1925       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
1933       class "vendor-classes" {
1934         match option vendor-class-identifier;
1935       }
1936
1937       subclass "vendor-classes" "SUNW.Ultra-5_10" {
1938         vendor-option-space SUNW;
1939         option SUNW.root-path "/export/root/sparc";
1940       }
1941
1942       subclass "vendor-classes" "SUNW.i86pc" {
1943         vendor-option-space SUNW;
1944         option SUNW.root-path "/export/root/i86pc";
1945       }
1946
1947       option SUNW.server-address 172.17.65.1;
1948       option SUNW.server-name "sundhcp-server17-1";
1949
1950       option vivso-sample.sample "Hello world!";
1951
1952       option docsis.tftp-servers ::1;
1953
1954
1955       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

SEE ALSO

1966       dhcpd.conf(5),    dhcpd.leases(5),    dhclient.conf(5),   dhcp-eval(5),
1967       dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.
1968

AUTHOR

1970       Information  about  Internet  Systems  Consortium  can  be   found   at
1971       https://www.isc.org.
1972
1973
1974
1975                                                               dhcp-options(5)
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