1dhcp-options(5)               File Formats Manual              dhcp-options(5)
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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
26       address  (e.g.,  239.254.197.10)  or  as  a  domain  name  (e.g.,  haa‐
27       gen.isc.org).  When entering a domain name, be sure  that  that  domain
28       name  resolves  to  a  single IP address. Additionally, please note the
29       software (dhcpd or dhclient) will only attempt to  resolve  the  domain
30       name  the  first  time  the option is needed. For example, if the next-
31       server option is defined as  a  domain  name,  dhcpd  will  attempt  to
32       resolve  it  while  responding to the first client query dhcpd receives
33       after startup. Should the domain's  address  subsequently  change,  the
34       software has to be restarted in order to pick up the change.
35
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
46       enclosed 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
109       option you would edit the includes/site.h file and comment out the def‐
110       inition 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
115       below  may  not  yet  be  implemented,  but  it is possible to use such
116       options by defining them in the configuration  file.   Please  see  the
117       DEFINING  NEW  OPTIONS heading later in this document for more informa‐
118       tion.
119
120       Some of the options documented here are automatically generated by  the
121       DHCP  server  or by clients, and cannot be configured by the user.  The
122       value of such an option can be used in the configuration  file  of  the
123       receiving DHCP protocol agent (server or client), for example in condi‐
124       tional expressions. However, the value of the option cannot be used  in
125       the  configuration  file  of  the  sending  agent, because the value is
126       determined only after the configuration file has been processed. In the
127       following  documentation,  such options will be shown as "not user con‐
128       figurable"
129
130       The standard options are:
131
132       option all-subnets-local flag;
133
134         This option specifies whether or not the client may assume  that  all
135         subnets  of  the  IP network to which the client is connected use the
136         same MTU as the subnet  of  that  network  to  which  the  client  is
137         directly connected.  A value of true indicates that all subnets share
138         the same MTU.  A value of false means that the client  should  assume
139         that  some subnets of the directly connected network may have smaller
140         MTUs.
141
142       option arp-cache-timeout uint32;
143
144         This option specifies the timeout in seconds for ARP cache entries.
145
146       option associated-ip ip-address [, ip-address... ];
147
148         This option is part of lease query.  It is used to return all of  the
149         IP addresses associated with a given DHCP client.
150
151         This option is not user configurable.
152
153       option bcms-controller-address ip-address [, ip-address... ];
154
155         This  option configures a list of IPv4 addresses for use as Broadcast
156         and Multicast Controller Servers ("BCMS").
157
158       option bcms-controller-names domain-list;
159
160         This option contains the domain names of local Broadcast  and  Multi‐
161         cast  Controller  Servers  ("BCMS")  controllers which the client may
162         use.
163
164       option bootfile-name text;
165
166         This option is used to identify a bootstrap file.   If  supported  by
167         the  client,  it should have the same effect as the filename declara‐
168         tion.  BOOTP clients are unlikely to support this option.  Some  DHCP
169         clients will support it, and others actually require it.
170
171       option boot-size uint16;
172
173         This  option  specifies the length in 512-octet blocks of the default
174         boot image for the client.
175
176       option broadcast-address ip-address;
177
178         This option specifies the broadcast address in use  on  the  client's
179         subnet.   Legal  values for broadcast addresses are specified in sec‐
180         tion 3.2.1.3 of STD 3 (RFC1122).
181
182       option capwap-ac-v4 ip-address [, ip-address ... ] ;
183
184         A list of IPv4 addresses of CAPWAP ACs that the  WTP  may  use.   The
185         addresses are listed in preference order.
186
187         This option is included based on RFC 5417.
188
189       option client-last-transaction-time uint32;
190
191         This option is part of lease query.  It allows the receiver to deter‐
192         mine the time of the most recent access by the client.  The value  is
193         a duration in seconds from when the client last communicated with the
194         DHCP server.
195
196         This option is not user configurable.
197
198       option cookie-servers ip-address [, ip-address...  ];
199
200         The cookie server option specifies a list of RFC 865  cookie  servers
201         available  to the client.  Servers should be listed in order of pref‐
202         erence.
203
204       option default-ip-ttl uint8;
205
206         This option specifies the default time-to-live that the client should
207         use on outgoing datagrams.
208
209       option default-tcp-ttl uint8;
210
211         This option specifies the default TTL that the client should use when
212         sending TCP segments.  The minimum value is 1.
213
214       option default-url string;
215
216         The format and meaning of this option is not described in  any  stan‐
217         dards document, but is claimed to be in use by Apple Computer.  It is
218         not known what clients  may  reasonably  do  if  supplied  with  this
219         option.  Use at your own risk.
220
221       option dhcp-client-identifier string;
222
223         This option can be used to specify a DHCP client identifier in a host
224         declaration, so that dhcpd can  find  the  host  record  by  matching
225         against the client identifier.
226
227         Please  be  aware that some DHCP clients, when configured with client
228         identifiers that are ASCII text, will prepend a  zero  to  the  ASCII
229         text.  So you may need to write:
230
231              option dhcp-client-identifier "\0foo";
232
233         rather than:
234
235              option dhcp-client-identifier "foo";
236
237       option dhcp-lease-time uint32;
238
239         This option is used in a client request (DHCPDISCOVER or DHCPREQUEST)
240         to allow the client to request a lease time for the IP address.  In a
241         server  reply  (DHCPOFFER), a DHCP server uses this option to specify
242         the lease time it is willing to offer.
243
244         This option is not directly user configurable in the server; refer to
245         the   max-lease-time   and   default-lease-time   server  options  in
246         dhcpd.conf(5).
247
248       option dhcp-max-message-size uint16;
249
250         This option, when sent by the client, specifies the maximum  size  of
251         any  response that the server sends to the client.  When specified on
252         the server, if  the  client  did  not  send  a  dhcp-max-message-size
253         option,  the  size  specified  on the server is used.  This works for
254         BOOTP as well as DHCP responses.
255
256       option dhcp-message text;
257
258         This option is used by a DHCP server to provide an error message to a
259         DHCP  client in a DHCPNAK message in the event of a failure. A client
260         may use this option in a DHCPDECLINE  message  to  indicate  why  the
261         client declined the offered parameters.
262
263         This option is not user configurable.
264
265       option dhcp-message-type uint8;
266
267         This  option,  sent  by both client and server, specifies the type of
268         DHCP message contained in the DHCP  packet.  Possible  values  (taken
269         directly from RFC2132) are:
270
271                      1     DHCPDISCOVER
272                      2     DHCPOFFER
273                      3     DHCPREQUEST
274                      4     DHCPDECLINE
275                      5     DHCPACK
276                      6     DHCPNAK
277                      7     DHCPRELEASE
278                      8     DHCPINFORM
279
280         This option is not user configurable.
281
282       option dhcp-option-overload uint8;
283
284         This  option  is  used  to  indicate  that the DHCP ´sname´ or ´file´
285         fields are being overloaded by using them to carry  DHCP  options.  A
286         DHCP  server  inserts  this  option  if  the returned parameters will
287         exceed the usual space allotted for options.
288
289         If this option is present, the client interprets the specified  addi‐
290         tional  fields  after  it  concludes  interpretation  of the standard
291         option fields.
292
293         Legal values for this option are:
294
295                      1     the ´file´ field is used to hold options
296                      2     the ´sname´ field is used to hold options
297                      3     both fields are used to hold options
298
299         This option is not user configurable.
300
301       option dhcp-parameter-request-list uint8 [, uint8... ];
302
303         This option, when sent by the client,  specifies  which  options  the
304         client  wishes  the  server  to  return.   Normally,  in the ISC DHCP
305         client, this is done using the request statement.  If this option  is
306         not  specified  by  the  client, the DHCP server will normally return
307         every option that is valid in scope and that  fits  into  the  reply.
308         When  this  option is specified on the server, the server returns the
309         specified options.  This can be  used  to  force  a  client  to  take
310         options  that  it hasn't requested, and it can also be used to tailor
311         the response of the DHCP server for clients that may need a more lim‐
312         ited set of options than those the server would normally return.
313
314       option dhcp-rebinding-time uint32;
315
316         This  option  specifies  the number of seconds from the time a client
317         gets an address until the client transitions to the REBINDING state.
318
319         This option is user configurable, but it will be ignored if the value
320         is greater than or equal to the lease time.
321
322         To  make DHCPv4+DHCPv6 migration easier in the future, any value con‐
323         figured in this option is also used as a DHCPv6 "T1" (renew) time.
324
325       option dhcp-renewal-time uint32;
326
327         This option specifies the number of seconds from the  time  a  client
328         gets an address until the client transitions to the RENEWING state.
329
330         This option is user configurable, but it will be ignored if the value
331         is greater than or equal to the rebinding time, or lease time.
332
333         To make DHCPv4+DHCPv6 migration easier in the future, any value  con‐
334         figured in this option is also used as a DHCPv6 "T2" (rebind) time.
335
336       option dhcp-requested-address ip-address;
337
338         This option is used by the client in a DHCPDISCOVER to request that a
339         particular IP address be assigned.
340
341         This option is not user configurable.
342
343       option dhcp-server-identifier ip-address;
344
345         This option is used in DHCPOFFER and DHCPREQUEST  messages,  and  may
346         optionally  be  included  in  the DHCPACK and DHCPNAK messages.  DHCP
347         servers include this option in the DHCPOFFER in order  to  allow  the
348         client  to  distinguish  between  lease offers.  DHCP clients use the
349         contents of the ´server identifier´ field as the destination  address
350         for  any DHCP messages unicast to the DHCP server.  DHCP clients also
351         indicate which of several lease offers is being accepted by including
352         this option in a DHCPREQUEST message.
353
354         The value of this option is the IP address of the server.
355
356         This option is not directly user configurable. See the server-identi‐
357         fier server option in dhcpd.conf(5).
358
359       option domain-name text;
360
361         This option specifies the domain name that  client  should  use  when
362         resolving hostnames via the Domain Name System.
363
364       option domain-name-servers ip-address [, ip-address...  ];
365
366         The domain-name-servers option specifies a list of Domain Name System
367         (STD 13, RFC 1035) name servers available  to  the  client.   Servers
368         should be listed in order of preference.
369
370       option domain-search domain-list;
371
372         The domain-search option specifies a ´search list´ of Domain Names to
373         be used by the client to  locate  not-fully-qualified  domain  names.
374         The  difference  between  this option and historic use of the domain-
375         name option for the same ends is  that  this  option  is  encoded  in
376         RFC1035 compressed labels on the wire.  For example:
377
378           option domain-search "example.com", "sales.example.com",
379                                "eng.example.com";
380
381       option extensions-path text;
382
383         This  option  specifies  the  name  of  a  file containing additional
384         options to be interpreted according to  the  DHCP  option  format  as
385         specified in RFC2132.
386
387       option finger-server ip-address [, ip-address... ];
388
389         The Finger server option specifies a list of Finger servers available
390         to the client.  Servers should be listed in order of preference.
391
392       option font-servers ip-address [, ip-address...  ];
393
394         This option specifies a list of X Window System Font  servers  avail‐
395         able to the client. Servers should be listed in order of preference.
396
397       option geoconf-civic string;
398
399         A string to hold the geoconf civic structure.
400
401         This option is included based on RFC 4776.
402
403       option host-name string;
404
405         This  option  specifies  the name of the client.  The name may or may
406         not be qualified with the local domain name (it is preferable to  use
407         the domain-name option to specify the domain name).  See RFC 1035 for
408         character set restrictions.  This option is only honored by dhclient-
409         script(8) if the hostname for the client machine is not set.
410
411       option ieee802-3-encapsulation flag;
412
413         This  option  specifies whether or not the client should use Ethernet
414         Version 2 (RFC 894) or IEEE 802.3 (RFC  1042)  encapsulation  if  the
415         interface is an Ethernet.  A value of false indicates that the client
416         should use RFC 894 encapsulation.  A value of  true  means  that  the
417         client should use RFC 1042 encapsulation.
418
419       option ien116-name-servers ip-address [, ip-address...  ];
420
421         The  ien116-name-servers  option  specifies  a  list  of IEN 116 name
422         servers available to the client.  Servers should be listed  in  order
423         of preference.
424
425       option impress-servers ip-address [, ip-address...  ];
426
427         The  impress-server option specifies a list of Imagen Impress servers
428         available to the client.  Servers should be listed in order of  pref‐
429         erence.
430
431       option interface-mtu uint16;
432
433         This  option specifies the MTU to use on this interface.  The minimum
434         legal value for the MTU is 68.
435
436       option ip-forwarding flag;
437
438         This option specifies whether the  client  should  configure  its  IP
439         layer  for packet forwarding.  A value of false means disable IP for‐
440         warding, and a value of true means enable IP forwarding.
441
442       option irc-server ip-address [, ip-address... ];
443
444         The IRC server option specifies a list of IRC  servers  available  to
445         the client.  Servers should be listed in order of preference.
446
447
448       option loader-configfile text
449
450         This  option  is  used to specify a boot loading configuration file a
451         PXE client should use.
452
453         This option is included based on RFC 5071.
454
455       option loader-pathprefix text
456
457         This option is used to specify a path prefix a PXE client should  use
458         in conjunction with the boot load configuration file.
459
460         This option is included based on RFC 5071.
461
462       option loader-reboottime uint32
463
464         This  option  is  used  to  dictate  the maximum amount of time a PXE
465         client should allow itself to achieve  configured  network  resources
466         before rebooting.
467
468         This option is included based on RFC 5071.
469
470       option log-servers ip-address [, ip-address...  ];
471
472         The  log-server  option  specifies  a list of MIT-LCS UDP log servers
473         available to the client.  Servers should be listed in order of  pref‐
474         erence.
475
476       option lpr-servers ip-address  [, ip-address...  ];
477
478         The  LPR  server  option  specifies  a  list of RFC 1179 line printer
479         servers available to the client.  Servers should be listed  in  order
480         of preference.
481
482       option mask-supplier flag;
483
484         This  option  specifies  whether  or not the client should respond to
485         subnet mask requests using ICMP.  A value of false indicates that the
486         client  should  not  respond.   A value of true means that the client
487         should respond.
488
489       option max-dgram-reassembly uint16;
490
491         This option specifies the  maximum  size  datagram  that  the  client
492         should be prepared to reassemble.  The minimum legal value is 576.
493
494       option merit-dump text;
495
496         This  option  specifies the path-name of a file to which the client's
497         core image should be dumped in the event  the  client  crashes.   The
498         path is formatted as a character string consisting of characters from
499         the NVT ASCII character set.
500
501       option mobile-ip-home-agent ip-address [, ip-address... ];
502
503         This option specifies a list of IP  addresses  indicating  mobile  IP
504         home  agents  available  to  the  client.  Agents should be listed in
505         order of preference, although normally there will be  only  one  such
506         agent.
507
508       option name-service-search uint16 [, uint6... ];
509
510         This option specifies a list of name services in the order the client
511         should attempt to use them.
512
513         This option is included based on RFC 2937.
514
515       option nds-context string;
516
517         The nds-context option specifies the  name  of  the  initial  Netware
518         Directory Service for an NDS client.
519
520       option nds-servers ip-address [, ip-address... ];
521
522         The  nds-servers  option  specifies  a  list  of  IP addresses of NDS
523         servers.
524
525       option nds-tree-name string;
526
527         The nds-tree-name option specifies NDS tree name that the NDS  client
528         should use.
529
530       option netbios-dd-server ip-address [, ip-address...  ];
531
532         The  NetBIOS  datagram  distribution server (NBDD) option specifies a
533         list of RFC 1001/1002 NBDD servers listed in order of preference.
534
535       option netbios-name-servers ip-address [, ip-address...];
536
537         The NetBIOS name  server  (NBNS)  option  specifies  a  list  of  RFC
538         1001/1002  NBNS  name servers listed in order of preference.  NetBIOS
539         Name Service is currently more commonly referred to  as  WINS.   WINS
540         servers can be specified using the netbios-name-servers option.
541
542       option netbios-node-type uint8;
543
544         The NetBIOS node type option allows NetBIOS over TCP/IP clients which
545         are configurable to be configured as described in RFC 1001/1002.  The
546         value  is  specified  as  a  single octet which identifies the client
547         type.
548
549         Possible node types are:
550
551         1    B-node: Broadcast - no WINS
552
553         2    P-node: Peer - WINS only
554
555         4    M-node: Mixed - broadcast, then WINS
556
557         8    H-node: Hybrid - WINS, then broadcast
558
559       option netbios-scope string;
560
561         The NetBIOS scope option specifies  the  NetBIOS  over  TCP/IP  scope
562         parameter  for the client as specified in RFC 1001/1002. See RFC1001,
563         RFC1002, and RFC1035 for character-set restrictions.
564
565       option netinfo-server-address ip-address [, ip-address... ];
566
567         The netinfo-server-address option has not been described in any  RFC,
568         but has been allocated (and is claimed to be in use) by Apple Comput‐
569         ers.  It's hard to say if the above is the correct  format,  or  what
570         clients  might  be  expected to do if values were configured.  Use at
571         your own risk.
572
573       option netinfo-server-tag text;
574
575         The netinfo-server-tag option has not been described in any RFC,  but
576         has  been allocated (and is claimed to be in use) by Apple Computers.
577         It's hard to say if the above is the correct format, or what  clients
578         might  be  expected to do if values were configured.  Use at your own
579         risk.
580
581       option nis-domain text;
582
583         This option specifies the name  of  the  client's  NIS  (Sun  Network
584         Information Services) domain.  The domain is formatted as a character
585         string consisting of characters from the NVT ASCII character set.
586
587       option nis-servers ip-address [, ip-address...  ];
588
589         This option specifies a list of IP addresses indicating  NIS  servers
590         available  to the client.  Servers should be listed in order of pref‐
591         erence.
592
593       option nisplus-domain text;
594
595         This option specifies the name of  the  client's  NIS+  domain.   The
596         domain  is  formatted  as a character string consisting of characters
597         from the NVT ASCII character set.
598
599       option nisplus-servers ip-address [, ip-address...  ];
600
601         This option specifies a list of IP addresses indicating NIS+  servers
602         available  to the client.  Servers should be listed in order of pref‐
603         erence.
604
605       option nntp-server ip-address [, ip-address... ];
606
607         The NNTP server option specifies a list of NNTP servers available  to
608         the client.  Servers should be listed in order of preference.
609
610       option non-local-source-routing flag;
611
612         This  option  specifies  whether  the  client should configure its IP
613         layer to allow forwarding of datagrams with non-local  source  routes
614         (see  Section  3.3.5 of [4] for a discussion of this topic).  A value
615         of false means disallow forwarding of such datagrams, and a value  of
616         true means allow forwarding.
617
618       option ntp-servers ip-address [, ip-address...  ];
619
620         This  option  specifies  a  list  of IP addresses indicating NTP (RFC
621         5905) servers available to the client.  Servers should be  listed  in
622         order of preference.
623
624       option nwip-domain string;
625
626         The  name  of  the  NetWare/IP domain that a NetWare/IP client should
627         use.
628
629       option nwip-suboptions string;
630
631         A sequence of suboptions for NetWare/IP clients  -  see  RFC2242  for
632         details.   Normally  this  option  is set by specifying specific Net‐
633         Ware/IP suboptions - see the NETWARE/IP SUBOPTIONS section  for  more
634         information.
635
636       option pxe-system-type uint16 [, uint16 ... ];
637
638         A list of one ore more 16-bit integers which allows a client to spec‐
639         ify its pre-boot architecture type(s).
640
641         This option is included based on RFC 4578.
642
643       option pxe-interface-id uint8 uint8 uint8
644
645         A three octet value which allows a  client  to  specify  its  network
646         interface type.
647
648         This option is included based on RFC 4578.
649
650       option pxe-client-id uint8 string
651
652         A  single  octet  indicating type, followed by a string that allows a
653         client to specify its PXE client identity.
654
655         This option is included based on RFC 4578.
656
657       option option-6rd uint8  uint8  ip6-address  ip-address  [,  ip-address
658       ...];
659
660         This  option  contains information about the rapid deployment option.
661         It is 8 bits of ipv4 mask length, 8 bits of  6rd  prefix  length,  an
662         ipv6  prefix  as  an  ipv6  address  and  a  list of one or more ipv4
663         addresses.
664
665         This option is included based on RFC 5969.
666
667       option pana-agent ip-address [, ip-address ... ] ;
668
669         A set of IPv4 addresses  of  a  PAA  for  the  client  to  use.   The
670         addresses are listed in preferred order.
671
672         This option is included based on RFC 5192.
673
674       option path-mtu-aging-timeout uint32;
675
676         This option specifies the timeout (in seconds) to use when aging Path
677         MTU values discovered by the mechanism defined in RFC 1191.
678
679       option path-mtu-plateau-table uint16 [, uint16...  ];
680
681         This option specifies a table of MTU sizes  to  use  when  performing
682         Path MTU Discovery as defined in RFC 1191.  The table is formatted as
683         a list of 16-bit unsigned integers, ordered from smallest to largest.
684         The minimum MTU value cannot be smaller than 68.
685
686       option pcode text;
687
688         This option specifies a string suitable for the TZ variable.
689
690         This option is included based on RFC 4833.
691
692       option perform-mask-discovery flag;
693
694         This option specifies whether or not the client should perform subnet
695         mask discovery using ICMP.  A  value  of  false  indicates  that  the
696         client should not perform mask discovery.  A value of true means that
697         the client should perform mask discovery.
698
699       option policy-filter ip-address ip-address
700                         [, ip-address ip-address...];
701
702         This option specifies policy filters for  non-local  source  routing.
703         The filters consist of a list of IP addresses and masks which specify
704         destination/mask pairs with which to filter incoming source routes.
705
706         Any source routed datagram whose next-hop address does not match  one
707         of the filters should be discarded by the client.
708
709         See STD 3 (RFC1122) for further information.
710
711       option pop-server ip-address [, ip-address... ];
712
713         The  POP3 server option specifies a list of POP3 servers available to
714         the client.  Servers should be listed in order of preference.
715
716       option rdnss-selection uint8 ip-address ip-address domain-name;
717
718         The rdnss-selection option specifies an 8 bit flags field, a  primary
719         and  secondary  ip  address  for  the name server and a domainlist of
720         domains for which the RDNSS has special knowledge.
721
722         This option is included based on RFC 6731.
723
724       option resource-location-servers ip-address
725                                     [, ip-address...];
726
727         This option specifies a list of RFC  887  Resource  Location  servers
728         available  to the client.  Servers should be listed in order of pref‐
729         erence.
730
731       option root-path text;
732
733         This option specifies the path-name that contains the  client's  root
734         disk.   The  path  is  formatted  as a character string consisting of
735         characters from the NVT ASCII character set.
736
737       option router-discovery flag;
738
739         This option specifies  whether  or  not  the  client  should  solicit
740         routers  using the Router Discovery mechanism defined in RFC 1256.  A
741         value of false indicates that the client should  not  perform  router
742         discovery.   A  value  of  true  means that the client should perform
743         router discovery.
744
745       option router-solicitation-address ip-address;
746
747         This option specifies the address to which the client should transmit
748         router solicitation requests.
749
750       option routers ip-address [, ip-address...  ];
751
752         The  routers  option  specifies a list of IP addresses for routers on
753         the client's subnet.  Routers should be listed in  order  of  prefer‐
754         ence.
755
756       option slp-directory-agent boolean ip-address [, ip-address... ];
757
758         This  option  specifies  two  things: the IP addresses of one or more
759         Service Location Protocol Directory Agents, and whether  the  use  of
760         these  addresses is mandatory.  If the initial boolean value is true,
761         the SLP agent should just use the IP addresses given.  If  the  value
762         is  false, the SLP agent may additionally do active or passive multi‐
763         cast discovery of SLP agents (see RFC2165 for details).
764
765         Please note that in this option and the slp-service-scope option, the
766         term  "SLP Agent" is being used to refer to a Service Location Proto‐
767         col agent running on a machine that is  being  configured  using  the
768         DHCP protocol.
769
770         Also,  please  be  aware that some companies may refer to SLP as NDS.
771         If you have an NDS directory agent whose address you need to  config‐
772         ure, the slp-directory-agent option should work.
773
774       option slp-service-scope boolean text;
775
776         The  Service  Location  Protocol  Service  Scope Option specifies two
777         things: a list of service scopes for SLP, and whether the use of this
778         list  is  mandatory.   If  the initial boolean value is true, the SLP
779         agent should only use the list of scopes  provided  in  this  option;
780         otherwise,  it  may use its own static configuration in preference to
781         the list provided in this option.
782
783         The text string should be a comma-separated list of scopes  that  the
784         SLP agent should use.  It may be omitted, in which case the SLP Agent
785         will use the aggregated list of scopes of all directory agents  known
786         to the SLP agent.
787
788       option smtp-server ip-address [, ip-address... ];
789
790         The  SMTP server option specifies a list of SMTP servers available to
791         the client.  Servers should be listed in order of preference.
792
793       option static-routes ip-address ip-address
794                         [, ip-address ip-address...];
795
796         This option specifies a list of static routes that the client  should
797         install  in its routing cache.  If multiple routes to the same desti‐
798         nation are specified, they are listed in descending order  of  prior‐
799         ity.
800
801         The  routes consist of a list of IP address pairs.  The first address
802         is the destination address, and the second address is the router  for
803         the destination.
804
805         The  default  route  (0.0.0.0) is an illegal destination for a static
806         route.  To specify the default route, use the routers option.   Also,
807         please note that this option is not intended for classless IP routing
808         - it does not include a subnet mask.  Since classless IP  routing  is
809         now  the most widely deployed routing standard, this option is virtu‐
810         ally useless, and is not implemented  by  any  of  the  popular  DHCP
811         clients, for example the Microsoft DHCP client.
812
813         NOTE to Fedora dhclient users:
814         dhclient-script  interprets  trailing 0 octets of the target as indi‐
815         cating the subnet class of the route, so for  the  following  static-
816         routes value:
817                 option static-routes 172.0.0.0 172.16.2.254,
818                                      192.168.0.0 192.168.2.254;
819         dhclient-script will create routes:
820                 172/8 via 172.16.2.254 dev $interface
821                 192.168/16 via 192.168.2.254 dev $interface
822
823       option classless-static-routes destination-descriptor ip-address
824                                   [, destination-descriptor ip-address...];
825
826         This option (see RFC3442) specifies a list of classless static routes
827         that the client should install in its routing cache.
828
829         This option can contain one or more static routes, each of which con‐
830         sists  of  a  destination descriptor and the IP address of the router
831         that should be used to reach that destination.
832
833         Many clients may not implement the Classless  Static  Routes  option.
834         DHCP  server  administrators  should  therefore  configure their DHCP
835         servers to send both a Router option and a  Classless  Static  Routes
836         option,  and  should specify the default router(s) both in the Router
837         option and in the Classless Static Routes option.
838
839         If the DHCP server returns both a Classless Static Routes option  and
840         a Router option, the DHCP client ignores the Router option.
841
842       option streettalk-directory-assistance-server ip-address
843                                                  [, ip-address...];
844
845         The  StreetTalk Directory Assistance (STDA) server option specifies a
846         list of STDA servers available to  the  client.   Servers  should  be
847         listed in order of preference.
848
849       option streettalk-server ip-address [, ip-address... ];
850
851         The  StreetTalk  server option specifies a list of StreetTalk servers
852         available to the client.  Servers should be listed in order of  pref‐
853         erence.
854
855       option subnet-mask ip-address;
856
857         The  subnet mask option specifies the client's subnet mask as per RFC
858         950.  If no subnet mask option is provided anywhere in  scope,  as  a
859         last  resort  dhcpd will use the subnet mask from the subnet declara‐
860         tion for the network on which an address is being assigned.  However,
861         any  subnet-mask  option declaration that is in scope for the address
862         being assigned will override the subnet mask specified in the  subnet
863         declaration.
864
865       option subnet-selection ip-address;
866
867         Sent  by  the client if an address is required in a subnet other than
868         the one that would  normally  be  selected  (based  on  the  relaying
869         address  of  the  connected subnet the request is obtained from). See
870         RFC3011. Note that the option number used by this server is 118; this
871         has  not  always  been the defined number, and some clients may use a
872         different value. Use of this option should be  regarded  as  slightly
873         experimental!
874
875       This option is not user configurable in the server.
876
877       option swap-server ip-address;
878
879         This specifies the IP address of the client's swap server.
880
881       option tftp-server-address ip-address [, ip-address... ];
882
883         This  option  configures a list of one or more IPv4 addresses of tftp
884         servers a client may use.
885
886         This option is included based on RFC 5859
887
888       option tcp-keepalive-garbage flag;
889
890         This option specifies whether or  not  the  client  should  send  TCP
891         keepalive  messages  with  an octet of garbage for compatibility with
892         older implementations.  A value of false  indicates  that  a  garbage
893         octet  should  not  be sent. A value of true indicates that a garbage
894         octet should be sent.
895
896       option tcp-keepalive-interval uint32;
897
898         This option specifies the interval (in seconds) that the  client  TCP
899         should  wait  before sending a keepalive message on a TCP connection.
900         The time is specified as a 32-bit unsigned integer.  A value of  zero
901         indicates  that  the client should not generate keepalive messages on
902         connections unless specifically requested by an application.
903
904       option tcode text;
905
906         This option specifies a name of a zone entry in the TZ database.
907
908         This option is included based on RFC 4833.
909
910       option tftp-server-name text;
911
912         This option is used to identify a TFTP server and,  if  supported  by
913         the  client,  should have the same effect as the server-name declara‐
914         tion.  BOOTP clients are unlikely to support this option.  Some  DHCP
915         clients will support it, and others actually require it.
916
917       option time-offset int32;
918
919         The time-offset option specifies the offset of the client's subnet in
920         seconds from Coordinated Universal Time (UTC).
921
922       option time-servers ip-address [, ip-address...  ];
923
924         The time-server option specifies a  list  of  RFC  868  time  servers
925         available  to the client.  Servers should be listed in order of pref‐
926         erence.
927
928       option trailer-encapsulation flag;
929
930         This option specifies whether or not the client should negotiate  the
931         use  of trailers (RFC 893 [14]) when using the ARP protocol.  A value
932         of false indicates that the client should not attempt to  use  trail‐
933         ers.   A  value  of  true means that the client should attempt to use
934         trailers.
935
936       option uap-servers text;
937
938         This option specifies a list of URLs, each pointing to a user authen‐
939         tication   service  that  is  capable  of  processing  authentication
940         requests encapsulated in the User Authentication Protocol (UAP).  UAP
941         servers can accept either HTTP 1.1 or SSLv3 connections.  If the list
942         includes a URL that does not contain a  port  component,  the  normal
943         default  port  is  assumed  (i.e.,  port 80 for http and port 443 for
944         https).  If the list includes a URL that does not contain a path com‐
945         ponent,  the path /uap is assumed.  If more than one URL is specified
946         in this list, the URLs are separated by spaces.
947
948       option user-class string;
949
950         This option is used by some DHCP clients as a way for users to  spec‐
951         ify  identifying  information  to  the client.  This can be used in a
952         similar way to the vendor-class-identifier option, but the  value  of
953         the  option  is  specified  by the user, not the vendor.  Most recent
954         DHCP clients have a way in the user interface to  specify  the  value
955         for this identifier, usually as a text string.
956
957       option v4-access-domain domain-name;
958
959         The  domain  name associated with the access network for use with LIS
960         Discovery.
961
962         This option is included based on RFC 5986.
963
964       option v4-lost domain-name;
965
966         The domain name of the LoST server for the client to use.
967
968         This option is included based on RFC 5223.
969
970       option vendor-class-identifier string;
971
972         This option is used by some DHCP clients to identify the vendor  type
973         and  possibly the configuration of a DHCP client.  The information is
974         a string of bytes whose contents are specific to the vendor  and  are
975         not  specified  in  a  standard.  To see what vendor class identifier
976         clients are sending, you can write the following in your DHCP  server
977         configuration file:
978
979         set vendor-string = option vendor-class-identifier;
980
981         This  will  result  in  all entries in the DHCP server lease database
982         file for clients that sent vendor-class-identifier options  having  a
983         set statement that looks something like this:
984
985         set vendor-string = "SUNW.Ultra-5_10";
986
987         The  vendor-class-identifier  option  is  normally  used  by the DHCP
988         server to determine the options that  are  returned  in  the  vendor-
989         encapsulated-options  option.   Please  see  the  VENDOR ENCAPSULATED
990         OPTIONS section later in this manual page for further information.
991
992       option vendor-encapsulated-options string;
993
994         The vendor-encapsulated-options option can contain  either  a  single
995         vendor-specific  value  or  one  or  more vendor-specific suboptions.
996         This option is not normally specified in the DHCP  server  configura‐
997         tion  file - instead, a vendor class is defined for each vendor, ven‐
998         dor class suboptions are defined, values  for  those  suboptions  are
999         defined, and the DHCP server makes up a response on that basis.
1000
1001         Some  default  behaviours  for  well-known  DHCP client vendors (cur‐
1002         rently, the Microsoft Windows 2000 DHCP client) are configured  auto‐
1003         matically,  but  otherwise this must be configured manually - see the
1004         VENDOR ENCAPSULATED OPTIONS section later in  this  manual  page  for
1005         details.
1006
1007       option vivso string;
1008
1009         The  vivso option can contain multiple separate options, one for each
1010         32-bit Enterprise ID.  Each Enterprise-ID discriminated  option  then
1011         contains additional options whose format is defined by the vendor who
1012         holds that ID.  This option is usually not configured  manually,  but
1013         rather is configured via intervening option definitions.  Please also
1014         see the VENDOR ENCAPSULATED OPTIONS section later in this manual page
1015         for details.
1016
1017       option www-server ip-address [, ip-address... ];
1018
1019         The  WWW  server  option specifies a list of WWW servers available to
1020         the client.  Servers should be listed in order of preference.
1021
1022       option x-display-manager ip-address [, ip-address...  ];
1023
1024         This option specifies a list of systems that are running the X Window
1025         System  Display  Manager  and are available to the client.  Addresses
1026         should be listed in order of preference.
1027

RELAY AGENT INFORMATION OPTION

1029       An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of
1030       encapsulated  options  that a relay agent can add to a DHCP packet when
1031       relaying it to the DHCP server.  The server can then make address allo‐
1032       cation  decisions (or whatever other decisions it wants) based on these
1033       options.  The server also returns these options in any replies it sends
1034       through  the  relay agent, so that the relay agent can use the informa‐
1035       tion in these options for delivery or accounting purposes.
1036
1037       The current draft defines two options.  To reference these  options  in
1038       the  dhcp server, specify the option space name, "agent", followed by a
1039       period, followed by the option name.  It  is  not  normally  useful  to
1040       define values for these options in the server, although it is permissi‐
1041       ble.  These options are not supported in the client.
1042
1043       option agent.circuit-id string;
1044
1045         The circuit-id suboption encodes an  agent-local  identifier  of  the
1046         circuit  from  which a DHCP client-to-server packet was received.  It
1047         is intended for use by agents in relaying DHCP responses back to  the
1048         proper circuit.  The format of this option is currently defined to be
1049         vendor-dependent, and will probably remain  that  way,  although  the
1050         current  draft allows for the possibility of standardizing the format
1051         in the future.
1052
1053       option agent.remote-id string;
1054
1055         The remote-id suboption encodes information about the remote host end
1056         of  a  circuit.   Examples of what it might contain include caller ID
1057         information, username information, remote ATM  address,  cable  modem
1058         ID, and similar things.  In principal, the meaning is not well-speci‐
1059         fied, and it should generally be assumed to be an opaque object  that
1060         is  administratively  guaranteed  to be unique to a particular remote
1061         end of a circuit.
1062
1063       option agent.DOCSIS-device-class uint32;
1064
1065         The DOCSIS-device-class suboption is intended to  convey  information
1066         about the host endpoint, hardware, and software, that either the host
1067         operating system or the DHCP server may not  otherwise  be  aware  of
1068         (but  the  relay  is  able to distinguish).  This is implemented as a
1069         32-bit field (4 octets), each bit representing a flag describing  the
1070         host  in  one  of these ways.  So far, only bit zero (being the least
1071         significant bit) is defined in RFC3256.  If this bit is set  to  one,
1072         the  host  is  considered  a  CPE Controlled Cable Modem (CCCM).  All
1073         other bits are reserved.
1074
1075       option agent.link-selection ip-address;
1076
1077         The link-selection suboption is provided by relay  agents  to  inform
1078         servers what subnet the client is actually attached to.  This is use‐
1079         ful in those cases where the giaddr (where responses must be sent  to
1080         the  relay agent) is not on the same subnet as the client.  When this
1081         option is present in a packet from a relay  agent,  the  DHCP  server
1082         will use its contents to find a subnet declared in configuration, and
1083         from here take one step further backwards to any  shared-network  the
1084         subnet  may  be  defined  within; the client may be given any address
1085         within that shared network, as normally appropriate.
1086

THE CLIENT FQDN SUBOPTIONS

1088       The Client FQDN option, currently defined in the Internet Draft  draft-
1089       ietf-dhc-fqdn-option-00.txt  is  not  a  standard yet, but is in suffi‐
1090       ciently wide use already that we have implemented it.  Due to the  com‐
1091       plexity  of  the  option  format, we have implemented it as a suboption
1092       space rather than a single option.  In general this option  should  not
1093       be  configured  by  the  user - instead it should be used as part of an
1094       automatic DNS update system.
1095
1096       option fqdn.no-client-update flag;
1097
1098         When the client sends this, if it is true, it means the  client  will
1099         not  attempt  to update its A record.  When sent by the server to the
1100         client, it means that the client should not update its own A record.
1101
1102       option fqdn.server-update flag;
1103
1104         When the client sends this to the server, it is requesting  that  the
1105         server  update  its A record.  When sent by the server, it means that
1106         the server has updated (or is about to update) the client's A record.
1107
1108       option fqdn.encoded flag;
1109
1110         If true, this indicates that the domain name included in  the  option
1111         is  encoded in DNS wire format, rather than as plain ASCII text.  The
1112         client normally sets this to false if it  doesn't  support  DNS  wire
1113         format  in  the  FQDN option.  The server should always send back the
1114         same value that the client sent.  When this value is set on the  con‐
1115         figuration side, it controls the format in which the fqdn.fqdn subop‐
1116         tion is encoded.
1117
1118       option fqdn.rcode1 flag;
1119
1120       option fqdn.rcode2 flag;
1121
1122         These options specify the result of the updates  of  the  A  and  PTR
1123         records,  respectively,  and  are only sent by the DHCP server to the
1124         DHCP client.  The values of these fields are those defined in the DNS
1125         protocol specification.
1126
1127       option fqdn.fqdn text;
1128
1129         Specifies the domain name that the client wishes to use.  This can be
1130         a fully-qualified domain name, or a single label.   If  there  is  no
1131         trailing  ´.´  character  in the name, it is not fully-qualified, and
1132         the server will generally update that name  in  some  locally-defined
1133         domain.
1134
1135       option fqdn.hostname --never set--;
1136
1137         This  option  should  never be set, but it can be read back using the
1138         option and config-option operators in an expression, in which case it
1139         returns  the first label in the fqdn.fqdn suboption - for example, if
1140         the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will
1141         be "foo".
1142
1143       option fqdn.domainname --never set--;
1144
1145         This  option  should  never be set, but it can be read back using the
1146         option and config-option operators in an expression, in which case it
1147         returns all labels after the first label in the fqdn.fqdn suboption -
1148         for example, if the value of fqdn.fqdn  is  "foo.example.com.",  then
1149         fqdn.domainname  will  be "example.com.".  If this suboption value is
1150         not set, it means that an unqualified  name  was  sent  in  the  fqdn
1151         option, or that no fqdn option was sent at all.
1152
1153       If  you wish to use any of these suboptions, we strongly recommend that
1154       you refer to the Client FQDN option draft (or standard, when it becomes
1155       a  standard) - the documentation here is sketchy and incomplete in com‐
1156       parison, and is just intended  for  reference  by  people  who  already
1157       understand the Client FQDN option specification.
1158

THE NETWARE/IP SUBOPTIONS

1160       RFC2242  defines  a  set  of encapsulated options for Novell NetWare/IP
1161       clients.  To use these options in the dhcp server, specify  the  option
1162       space  name, "nwip", followed by a period, followed by the option name.
1163       The following options can be specified:
1164
1165       option nwip.nsq-broadcast flag;
1166
1167         If true, the client should use the NetWare Nearest  Server  Query  to
1168         locate  a  NetWare/IP  server.  The behaviour of the Novell client if
1169         this suboption is false, or is not present, is not specified.
1170
1171       option nwip.preferred-dss ip-address [, ip-address... ];
1172
1173         This suboption specifies a list of up to five IP addresses,  each  of
1174         which  should  be  the  IP address of a NetWare Domain SAP/RIP server
1175         (DSS).
1176
1177       option nwip.nearest-nwip-server ip-address
1178                                    [, ip-address...];
1179
1180         This suboption specifies a list of up to five IP addresses,  each  of
1181         which should be the IP address of a Nearest NetWare IP server.
1182
1183       option nwip.autoretries uint8;
1184
1185         Specifies the number of times that a NetWare/IP client should attempt
1186         to communicate with a given DSS server at startup.
1187
1188       option nwip.autoretry-secs uint8;
1189
1190         Specifies the number of seconds that a Netware/IP client should  wait
1191         between  retries  when  attempting to establish communications with a
1192         DSS server at startup.
1193
1194       option nwip.nwip-1-1 uint8;
1195
1196         If true, the NetWare/IP client should support NetWare/IP version  1.1
1197         compatibility.   This is only needed if the client will be contacting
1198         Netware/IP version 1.1 servers.
1199
1200       option nwip.primary-dss ip-address;
1201
1202         Specifies the IP address of the Primary Domain SAP/RIP Service server
1203         (DSS)  for  this  NetWare/IP  domain.   The NetWare/IP administration
1204         utility uses this value as Primary DSS server when configuring a sec‐
1205         ondary DSS server.
1206

STANDARD DHCPV6 OPTIONS

1208       DHCPv6 options differ from DHCPv4 options partially due to using 16-bit
1209       code and length tags, but semantically zero-length options are legal in
1210       DHCPv6,  and  multiple  options  are  treated  differently.  Whereas in
1211       DHCPv4 multiple options would be concatenated to form  one  option,  in
1212       DHCPv6  they are expected to be individual instantiations.  Understand‐
1213       ably, many options are not "allowed" to have multiple  instances  in  a
1214       packet - normally these are options which are digested by the DHCP pro‐
1215       tocol software, and not by users or applications.
1216
1217       option dhcp6.client-id string;
1218
1219         This option specifies the client's DUID identifier.  DUIDs are  simi‐
1220         lar  but  different  from DHCPv4 client identifiers - there are docu‐
1221         mented duid types:
1222
1223         duid-llt
1224
1225         duid-en
1226
1227         duid-ll
1228
1229         This value should not  be  configured,  but  rather  is  provided  by
1230         clients and treated as an opaque identifier key blob by servers.
1231
1232       option dhcp6.server-id string;
1233
1234         This option specifies the server's DUID identifier.  One may use this
1235         option to configure an opaque binary blob for your  server's  identi‐
1236         fier.
1237
1238       option dhcp6.ia-na string;
1239
1240         The  Identity Association for Non-temporary Addresses (ia-na) carries
1241         assigned addresses that are not temporary addresses for  use  by  the
1242         DHCPv6  client.   This  option is produced by the DHCPv6 server soft‐
1243         ware, and should not be configured.
1244
1245       option dhcp6.ia-ta string;
1246
1247         The Identity Association for Temporary Addresses (ia-ta) carries tem‐
1248         porary  addresses,  which may change upon every renewal.  There is no
1249         support for this in the current DHCPv6 software.
1250
1251       option dhcp6.ia-addr string;
1252
1253         The Identity Association Address option is encapsulated inside  ia-na
1254         or  ia-ta  options  in  order  to represent addresses associated with
1255         those IA's.  These options  are  manufactured  by  the  software,  so
1256         should not be configured.
1257
1258       option dhcp6.oro uint16 [ , uint16, ... ];
1259
1260         The  Option  Request  Option  ("ORO") is the DHCPv6 equivalent of the
1261         parameter-request-list.  Clients supply this option to ask servers to
1262         reply with options relevant to their needs and use.  This option must
1263         not be directly configured, the request syntax in  dhclient.conf  (5)
1264         should be used instead.
1265
1266       option dhcp6.preference uint8;
1267
1268         The  preference  option informs a DHCPv6 client which server is ´pre‐
1269         ferred´ for use on a given subnet.  This preference is  only  applied
1270         during  the  initial stages of configuration - once a client is bound
1271         to an IA, it will remain bound to that IA until it is no longer valid
1272         or  has  expired.  This value may be configured on the server, and is
1273         digested by the client software.
1274
1275       option dhcp6.elapsed-time uint16;
1276
1277         The elapsed-time option is constructed by the DHCPv6 client software,
1278         and  is  potentially  consumed by intermediaries.  This option should
1279         not be configured.
1280
1281       option dhcp6.relay-msg string;
1282
1283         The relay-msg option is constructed by intervening DHCPv6 relay agent
1284         software.   This option is entirely used by protocol software, and is
1285         not meant for user configuration.
1286
1287       option dhcp6.unicast ip6-address;
1288
1289         The unicast option is provided by DHCPv6 servers  which  are  willing
1290         (or  prefer)  to receive Request, Renew, Decline, and Release packets
1291         from their clients via unicast.  Normally, DHCPv6 clients will multi‐
1292         cast  these messages.  Per RFC 3315, the server will reject a unicast
1293         message received from a client unless it previously  sent  (or  would
1294         have  sent)  the  unicast  option to that client.  This option may be
1295         configured on the server at the  global  and  shared  network  level.
1296         When  a  unicast  message  is  received, the server will check for an
1297         applicable definition of the unicast option.  If such  an  option  is
1298         found the message will be accepted, if not it will be rejected.
1299
1300       option dhcp6.status-code status-code [ string ] ;
1301
1302         The  status-code  option  is  provided  by  DHCPv6  servers to inform
1303         clients of error  conditions  during  protocol  communication.   This
1304         option  is manufactured and digested by protocol software, and should
1305         not be configured.
1306
1307       option dhcp6.rapid-commit ;
1308
1309         The rapid-commit option is a zero-length option that clients  use  to
1310         indicate their desire to enter into rapid-commit with the server.
1311
1312       option dhcp6.vendor-opts string;
1313
1314         The  vendor-opts option is actually an encapsulated sub-option space,
1315         in which each Vendor-specific Information Option (VSIO) is identified
1316         by  a  32-bit  Enterprise-ID  number.  The encapsulated option spaces
1317         within these options are defined by the vendors.
1318
1319         To make use of this option, the best way is to  examine  the  section
1320         titled  VENDOR  ENCAPSULATED  OPTIONS  below,  in particular the bits
1321         about the "vsio" option space.
1322
1323       option dhcp6.interface-id string;
1324
1325         The interface-id option is manufactured by relay agents, and  may  be
1326         used  to guide configuration differentiating clients by the interface
1327         they are remotely attached to.  It does not make sense to configure a
1328         value for this option, but it may make sense to inspect its contents.
1329
1330       option dhcp6.reconf-msg dhcpv6-message;
1331
1332         The reconf-msg option is manufactured by servers, and sent to clients
1333         in Reconfigure messages to inform them of  what  message  the  client
1334         should Reconfigure using.  There is no support for DHCPv6 Reconfigure
1335         extensions, and this option is documented informationally only.
1336
1337       option dhcp6.reconf-accept ;
1338
1339         The reconf-accept option is included by DHCPv6 clients  that  support
1340         the Reconfigure extensions, advertising that they will respond if the
1341         server were to ask them to Reconfigure.   There  is  no  support  for
1342         DHCPv6 Reconfigure extensions, and this option is documented informa‐
1343         tionally only.
1344
1345       option dhcp6.sip-servers-names domain-list;
1346
1347         The sip-servers-names option allows SIP clients to locate a local SIP
1348         server  that  is  to  be  used  for  all outbound SIP requests, a so-
1349         called"outbound proxy server."  If you wish to use  manually  entered
1350         IPv6  addresses  instead, please see the sip-servers-addresses option
1351         below.
1352
1353       option dhcp6.sip-servers-addresses ip6-address [, ip6-address ... ] ;
1354
1355         The sip-servers-addresses option allows SIP clients to locate a local
1356         SIP  server  that  is to be used for all outbound SIP requests, a so-
1357         called "outbound proxy servers."  If you wish  to  use  domain  names
1358         rather  than  IPv6 addresses, please see the sip-servers-names option
1359         above.
1360
1361       option dhcp6.name-servers ip6-address [, ip6-address ... ] ;
1362
1363         The name-servers option instructs  clients  about  locally  available
1364         recursive  DNS servers.  It is easiest to describe this as the "name‐
1365         server" line in /etc/resolv.conf.
1366
1367       option dhcp6.domain-search domain-list;
1368
1369         The domain-search option specifies the client's domain search path to
1370         be  applied to recursive DNS queries.  It is easiest to describe this
1371         as the "search" line in /etc/resolv.conf.
1372
1373       option dhcp6.ia-pd string;
1374
1375         The ia-pd option is manufactured by clients and servers to  create  a
1376         Prefix Delegation binding - to delegate an IPv6 prefix to the client.
1377         It is not directly edited in dhcpd.conf(5) or  dhclient.conf(5),  but
1378         rather is manufactured and consumed by the software.
1379
1380       option dhcp6.ia-prefix string;
1381
1382         The ia-prefix option is placed inside ia-pd options in order to iden‐
1383         tify the prefix(es) allocated to the  client.   It  is  not  directly
1384         edited  in  dhcpd.conf(5) or dhclient.conf(5), but rather is manufac‐
1385         tured and consumed by the software.
1386
1387       option dhcp6.nis-servers ip6-address [, ip6-address ... ] ;
1388
1389         The nis-servers option identifies, in order, NIS servers available to
1390         the client.
1391
1392       option dhcp6.nisp-servers ip6-address [, ip6-address ... ] ;
1393
1394         The  nisp-servers option identifies, in order, NIS+ servers available
1395         to the client.
1396
1397       option nis-domain-name domain-list;
1398
1399         The nis-domain-name option specifies the NIS domain name  the  client
1400         is expected to use, and is related to the nis-servers option.
1401
1402       option dhcp6.nis-domain-name domain-name;
1403
1404         The dhcp6.nis-domain-name option specifies NIS domain name the client
1405         is expected to use, and is related to dhcp6.nis-servers option.
1406
1407       option nisp-domain-name domain-list;
1408
1409         The nisp-domain-name option specifies the NIS+ domain name the client
1410         is expected to use, and is related to the nisp-servers option.
1411
1412       option dhcp6.nisp-domain-name domain-name;
1413
1414         The  dhcp6.nis-domain-name  option  specifies  NIS+  domain  name the
1415         client is expected to  use,  and  is  related  to  dhcp6.nisp-servers
1416         option.
1417
1418       option dhcp6.sntp-servers ip6-address [, ip6-address ... ] ;
1419
1420         The sntp-servers option specifies a list of local SNTP servers avail‐
1421         able for the client to synchronize their clocks.
1422
1423       option dhcp6.info-refresh-time uint32;
1424
1425         The info-refresh-time option gives DHCPv6 clients using  Information-
1426         request messages a hint as to how long they should between refreshing
1427         the information they were given.  Note that this option will only  be
1428         delivered  to the client, and be likely to affect the client's behav‐
1429         iour, if the client requested the option.
1430
1431       option dhcp6.bcms-server-d domain-list;
1432
1433         The bcms-server-d option contains the  domain  names  of  local  BCMS
1434         (Broadcast  and  Multicast  Control  Services)  controllers which the
1435         client may use.
1436
1437       option dhcp6.bcms-server-a ip6-address [, ip6-address ... ] ;
1438
1439         The bcms-server-a option contains the IPv6 addresses  of  local  BCMS
1440         (Broadcast  and  Multicast  Control  Services)  controllers which the
1441         client may use.
1442
1443       option dhcp6.geoconf-civic string;
1444
1445         A string to hold the geoconf civic structure.
1446
1447         This option is included based on RFC 4776.
1448
1449       option dhcp6.remote-id string;
1450
1451         The remote-id option is constructed by relay agents,  to  inform  the
1452         server of details pertaining to what the relay knows about the client
1453         (such as what port it is attached to, and so forth).  The contents of
1454         this  option  have  some vendor-specific structure (similar to VSIO),
1455         but we have chosen to treat this option as an opaque field.
1456
1457       option dhcp6.subscriber-id string;
1458
1459         The subscriber-id option is an opaque field  provided  by  the  relay
1460         agent,  which provides additional information about the subscriber in
1461         question.  The exact contents of this option depend upon  the  vendor
1462         and/or the operator's configuration of the remote device, and as such
1463         is an opaque field.
1464
1465       option dhcp6.fqdn string;
1466
1467         The fqdn option is normally constructed by the client or server,  and
1468         negotiates the client's Fully Qualified Domain Name, as well as which
1469         party is responsible for Dynamic DNS Updates.  See the section on the
1470         Client  FQDN  SubOptions for full details (the DHCPv4 and DHCPv6 FQDN
1471         options use the same "fqdn." encapsulated space, so are in  all  ways
1472         identical).
1473
1474       option dhcp6.pana-agent ip6-address [, ip6-address ... ] ;
1475
1476         A  set  of  IPv6  addresses  of  a  PAA  for  the client to use.  The
1477         addresses are listed in preferred order.
1478
1479         This option is included based on RFC 5192.
1480
1481       option dhcp6.new-posix-timezone text;
1482
1483         This option specifies a string suitable for the TZ variable.
1484
1485         This option is included based on RFC 4833.
1486
1487       option dhcp6.new-tzdb-timezone text;
1488
1489         This option specifies a name of a zone entry in the TZ database.
1490
1491         This option is included based on RFC 4833.
1492
1493       option dhcp6.ero uint16 [, uint16 ... ] ;
1494
1495         A list of the options requested by the relay agent.
1496
1497         This option is included based on RFC 4994.
1498
1499       option dhcp6.lq-query string;
1500
1501         The lq-query option is used internally for lease query.
1502
1503       option dhcp6.client-data string;
1504
1505         The client-data option is used internally for lease query.
1506
1507       option dhcp6.clt-time uint32;
1508
1509         The clt-time option is used internally for lease query.
1510
1511       option dhcp6.lq-relay-data ip6-address string;
1512
1513         The lq-relay-data option is used internally for lease query.
1514
1515       option dhcp6.lq-client-link ip6-address [, ip6-address ... ] ;
1516
1517         The lq-client-link option is used internally for lease query.
1518
1519       option dhcp6.v6-lost domain-name;
1520
1521         The domain name of the LoST server for the client to use.
1522
1523         This option is included based on RFC 5223.
1524
1525       option dhcp6.capwap-ac-v6 ip6-address [, ip6-address ... ] ;
1526
1527         A list of IPv6 addresses of CAPWAP ACs that the  WTP  may  use.   The
1528         addresses are listed in preference order.
1529
1530         This option is included based on RFC 5417.
1531
1532       option dhcp6.relay-id string;
1533
1534         The DUID for the relay agent.
1535
1536         This option is included based on RFC 5460.
1537
1538       option dhcp6.v6-access-domain domain-name;
1539
1540         The  domain  name associated with the access network for use with LIS
1541         Discovery.
1542
1543         This option is included based on RFC5986.
1544
1545       option dhcp6.sip-ua-cs-list domain-list;
1546
1547         The list of domain names in the SIP User Agent Configuration  Service
1548         Domains.
1549
1550         This option is included based on RFC 6011.
1551
1552       option dhcp6.bootfile-url text;
1553
1554         The URL for a boot file.
1555
1556         This option is included based on RFC 5970.
1557
1558       option dhcp6.bootfile-param string;
1559
1560         A  string  for the parameters to the bootfile.  See RFC 5970 for more
1561         description of the layout of the parameters within the string.
1562
1563         This option is included based on RFC 5970.
1564
1565       option dhcp6.client-arch-type uint16 [, uint16 ... ] ;
1566
1567         A list of one or more architecture types described as 16 bit values.
1568
1569         This option is included based on RFC 5970.
1570
1571       option dhcp6.nii uint8 uint8 uint8;
1572
1573         The client network interface identitier option  supplies  information
1574         about  a  client's  level of UNDI support.  The values are, in order,
1575         the type, the major value and the minor value.
1576
1577         This option is included based on RFC5970.
1578
1579       option dhcp6.aftr-name domain-name;
1580
1581         A domain name of the AFTR tunnel endpoint.
1582
1583         This option is included based on RFC 6334.
1584
1585       option dhcp6.erp-local-domain-name domain-name;
1586
1587         A domain name for the ERP domain.
1588
1589         This option is included based on RFC 6440.
1590
1591       option dhcp6.rdnss-selection ip6-address uint8 domain-name;
1592
1593         RDNSS information consists of an IPv6 address  of  RDNSS,  an  8  bit
1594         flags field and a domain-list of domains for which the RDNSS has spe‐
1595         cial knowledge.
1596
1597         This option is included based on RFC 6731.
1598
1599       option dhcp6.client-linklayer-addr string;
1600
1601         A client link-layer address.  The first two bytes must be the type of
1602         the link-layer followed by the address itself.
1603
1604         This option is included based on RFC 6939.
1605
1606       option dhcp6.link-address ip6-address;
1607
1608         An  IPv6  address used by a relay agent to indicate to the server the
1609         link on which the client is located.
1610
1611         This option is included based on RFC 6977.
1612
1613       option dhcp6.solmax-rt uint32;
1614
1615         A value to override the default for SOL_MAX_RT.  This  is  a  32  bit
1616         value.
1617
1618         This option is included based on RFC 7083.
1619
1620       option dhcp6.inf-max-rt uint32;
1621
1622         A  value  to  override  the default for INF_MAX_RT.  This is a 32 bit
1623         value.
1624
1625         This option is included based on RFC 7083.
1626

ACCESSING DHCPV6 RELAY OPTIONS

1628       v6relay (relay-number, option) This option allows access to  an  option
1629       that  has  been added to a packet by a relay agent.  Relay-number value
1630       selects the relay to examine and option is  the  option  to  find.   In
1631       DHCPv6  each  relay  encapsulates  the  entire previous message into an
1632       option, adds its own options (if any) and  sends  the  result  onwards.
1633       The  RFC  specifies a limit of 32 hops.  A relay-number of 0 is a no-op
1634       and means don't look at the relays.  1 is the relay that is closest  to
1635       the  client,  2  would  be  the next in from the client and so on.  Any
1636       value greater than the max number of hops is which is  closest  to  the
1637       server  independent of number.  To use this option in a class statement
1638       you would have something like this:
1639
1640       match if v6relay(1, option dhcp6.subscriber-id) = "client_1";
1641

DEFINING NEW OPTIONS

1643       The Internet Systems Consortium DHCP  client  and  server  provide  the
1644       capability to define new options.  Each DHCP option has a name, a code,
1645       and a structure.  The name is used by you to refer to the option.   The
1646       code  is  a  number,  used by the DHCP server and client to refer to an
1647       option.  The structure describes what the contents of an  option  looks
1648       like.
1649
1650       To define a new option, you need to choose a name for it that is not in
1651       use for some other option - for  example,  you  can't  use  "host-name"
1652       because  the DHCP protocol already defines a host-name option, which is
1653       documented earlier in this manual page.   If  an  option  name  doesn't
1654       appear  in  this  manual page, you can use it, but it's probably a good
1655       idea to put some kind of unique string at the beginning so you  can  be
1656       sure  that future options don't take your name.  For example, you might
1657       define an option, "local-host-name", feeling some  confidence  that  no
1658       official DHCP option name will ever start with "local".
1659
1660       Once you have chosen a name, you must choose a code.  All codes between
1661       224 and 254 are reserved as ´site-local´ DHCP options, so you can  pick
1662       any  one of these for your site (not for your product/application).  In
1663       RFC3942, site-local space was moved from starting at 128 to starting at
1664       224.   In  practice,  some vendors have interpreted the protocol rather
1665       loosely and have used option code values greater than  128  themselves.
1666       There's  no  real  way  to avoid this problem, and it was thought to be
1667       unlikely to cause too much trouble in practice.  If you come  across  a
1668       vendor-documented  option code in either the new or old site-local spa‐
1669       ces, please contact your vendor and inform them about rfc3942.
1670
1671       The structure of an option is simply the format  in  which  the  option
1672       data  appears.   The  ISC  DHCP  server currently supports a few simple
1673       types, like integers, booleans, strings and IP addresses, and  it  also
1674       supports  the  ability  to  define  arrays of single types or arrays of
1675       fixed sequences of types.
1676
1677       New options are declared as follows:
1678
1679       option new-name code new-code = definition ;
1680
1681       The values of new-name and new-code should be the name you have  chosen
1682       for the new option and the code you have chosen.  The definition should
1683       be the definition of the structure of the option.
1684
1685       The following simple option type definitions are supported:
1686
1687       BOOLEAN
1688
1689       option new-name code new-code = boolean ;
1690
1691       An option of type boolean is a flag with a value of either  on  or  off
1692       (or true or false).  So an example use of the boolean type would be:
1693
1694       option use-zephyr code 180 = boolean;
1695       option use-zephyr on;
1696
1697       INTEGER
1698
1699       option new-name code new-code = sign integer width ;
1700
1701       The  sign  token should either be blank, unsigned or signed.  The width
1702       can be either 8, 16 or 32, and refers to the  number  of  bits  in  the
1703       integer.   So for example, the following two lines show a definition of
1704       the sql-connection-max option and its use:
1705
1706       option sql-connection-max code 192 = unsigned integer 16;
1707       option sql-connection-max 1536;
1708
1709       IP-ADDRESS
1710
1711       option new-name code new-code = ip-address ;
1712
1713       An option whose structure is an IP address can be expressed either as a
1714       domain name or as a dotted quad.  So the following is an example use of
1715       the ip-address type:
1716
1717       option sql-server-address code 193 = ip-address;
1718       option sql-server-address sql.example.com;
1719
1720       IP6-ADDRESS
1721
1722       option new-name code new-code = ip6-address ;
1723
1724       An option whose structure is an IPv6 address must  be  expressed  as  a
1725       valid IPv6 address.  The following is an example use of the ip6-address
1726       type:
1727
1728       option dhcp6.some-server code 1234 = array of ip6-address;
1729       option dhcp6.some-server 3ffe:bbbb:aaaa:aaaa::1, 3ffe:bbbb:aaaa:aaaa::2;
1730
1731
1732       TEXT
1733
1734       option new-name code new-code = text ;
1735
1736       An option whose type is text will encode an  ASCII  text  string.   For
1737       example:
1738
1739       option sql-default-connection-name code 194 = text;
1740       option sql-default-connection-name "PRODZA";
1741
1742
1743       DATA STRING
1744
1745       option new-name code new-code = string ;
1746
1747       An  option whose type is a data string is essentially just a collection
1748       of bytes, and can be specified either as quoted  text,  like  the  text
1749       type,  or  as  a list of hexadecimal contents separated by colons whose
1750       values must be between 0 and FF.  For example:
1751
1752       option sql-identification-token code 195 = string;
1753       option sql-identification-token 17:23:19:a6:42:ea:99:7c:22;
1754
1755
1756       DOMAIN-LIST
1757
1758       option new-name code new-code = domain-list [compressed] ;
1759
1760       An option whose type is domain-list is an  RFC1035  formatted  (on  the
1761       wire,  "DNS  Format")  list  of domain names, separated by root labels.
1762       The optional compressed keyword indicates if the option should be  com‐
1763       pressed  relative  to  the start of the option contents (not the packet
1764       contents).
1765
1766       When in doubt, omit the compressed keyword.  When the software receives
1767       an  option that is compressed and the compressed keyword is omitted, it
1768       will still decompress the  option  (relative  to  the  option  contents
1769       field).   The  keyword only controls whether or not transmitted packets
1770       are compressed.
1771
1772       Note that when domain-list formatted options are output as  environment
1773       variables  to dhclient-script(8), the standard DNS -escape mechanism is
1774       used: they are decimal.  This is  appropriate  for  direct  use  in  eg
1775       /etc/resolv.conf.
1776
1777
1778       ENCAPSULATION
1779
1780       option new-name code new-code = encapsulate identifier ;
1781
1782       An  option  whose  type is encapsulate will encapsulate the contents of
1783       the option space specified in  identifier.   Examples  of  encapsulated
1784       options in the DHCP protocol as it currently exists include the vendor-
1785       encapsulated-options option,  the  netware-suboptions  option  and  the
1786       relay-agent-information option.
1787
1788       option space local;
1789       option local.demo code 1 = text;
1790       option local-encapsulation code 197 = encapsulate local;
1791       option local.demo "demo";
1792
1793
1794       ARRAYS
1795
1796       Options  can  contain  arrays  of any of the above types except for the
1797       text and data string types, which aren't currently supported in arrays.
1798       An example of an array definition is as follows:
1799
1800       option kerberos-servers code 200 = array of ip-address;
1801       option kerberos-servers 10.20.10.1, 10.20.11.1;
1802
1803       RECORDS
1804
1805       Options  can  also  contain data structures consisting of a sequence of
1806       data types, which is sometimes called a record type.  For example:
1807
1808       option contrived-001 code 201 = { boolean, integer 32, text };
1809       option contrived-001 on 1772 "contrivance";
1810
1811       It's also possible to have options that  are  arrays  of  records,  for
1812       example:
1813
1814       option new-static-routes code 201 = array of {
1815            ip-address, ip-address, ip-address, integer 8 };
1816       option static-routes
1817            10.0.0.0 255.255.255.0 net-0-rtr.example.com 1,
1818            10.0.1.0 255.255.255.0 net-1-rtr.example.com 1,
1819            10.2.0.0 255.255.224.0 net-2-0-rtr.example.com 3;
1820
1821

VENDOR ENCAPSULATED OPTIONS

1823       The DHCP protocol defines the vendor-encapsulated-options option, which
1824       allows vendors to define their own options that will be  sent  encapsu‐
1825       lated in a standard DHCP option.  It also defines the Vendor Identified
1826       Vendor Sub Options option ("VIVSO"), and the  DHCPv6  protocol  defines
1827       the  Vendor-specific Information Option ("VSIO").  The format of all of
1828       these options is usually internally a string of options,  similarly  to
1829       other  normal  DHCP options.  The VIVSO and VSIO options differ in that
1830       they contain options that correspond to  vendor  Enterprise-ID  numbers
1831       (assigned  by  IANA), which then contain options according to each Ven‐
1832       dor's specifications.  You will need to refer to your vendor's documen‐
1833       tation in order to form options to their specification.
1834
1835       The  value  of  these options can be set in one of two ways.  The first
1836       way is to simply specify the data directly, using a text  string  or  a
1837       colon-separated  list of hexadecimal values.  For help in forming these
1838       strings, please refer to RFC2132 for the DHCPv4 Vendor Specific  Infor‐
1839       mation  Option,  RFC3925  for  the  DHCPv4 Vendor Identified Vendor Sub
1840       Options, or RFC3315 for the DHCPv6 Vendor-specific Information  Option.
1841       For example:
1842
1843       option vendor-encapsulated-options
1844           2:4:
1845            AC:11:41:1:
1846           3:12:
1847            73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:
1848           4:12:
1849            2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
1850       option vivso
1851           00:00:09:bf:0E:
1852            01:0c:
1853                48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1854       option dhcp6.vendor-opts
1855           00:00:09:bf:
1856            00:01:00:0c:
1857                48:65:6c:6c:6f:20:77:6f:72:6c:64:21;
1858
1859       The  second  way  of  setting the value of these options is to have the
1860       DHCP server generate a vendor-specific option buffer.  To do this,  you
1861       must  do  four  things:  define an option space, define some options in
1862       that option space, provide values  for  them,  and  specify  that  that
1863       option space should be used to generate the relevant option.
1864
1865       To define a new option space in which vendor options can be stored, use
1866       the option space statement:
1867
1868       option space name [ [ code width number ] [ length  width  number  ]  [
1869       hash size number ] ] ;
1870
1871       Where  the  numbers  following  code width, length width, and hash size
1872       respectively identify the number  of  bytes  used  to  describe  option
1873       codes,  option  lengths,  and the size in buckets of the hash tables to
1874       hold options in this space (most DHCPv4 option spaces use 1 byte  codes
1875       and  lengths,  which  is the default, whereas most DHCPv6 option spaces
1876       use 2 byte codes and lengths).
1877
1878       The code and length widths are used in DHCP protocol - you must config‐
1879       ure  these numbers to match the applicable option space you are config‐
1880       uring.  They each default to 1.  Valid values for code widths are 1,  2
1881       or  4.   Valid  values  for  length  widths are 0, 1 or 2.  Most DHCPv4
1882       option spaces use 1 byte codes  and  lengths,  which  is  the  default,
1883       whereas  most  DHCPv6  option  spaces  use 2 byte codes and lengths.  A
1884       zero-byte length produces options similar to the DHCPv6 Vendor-specific
1885       Information Option - but not their contents!
1886
1887       The  hash size defaults depend upon the code width selected, and may be
1888       254 or 1009.  Valid values range between 1 and 65535.   Note  that  the
1889       higher  you  configure this value, the more memory will be used.  It is
1890       considered good practice to configure a value that is  slightly  larger
1891       than  the  estimated number of options you plan to configure within the
1892       space.  Previous versions of ISC DHCP (up to and including DHCP 3.0.*),
1893       this value was fixed at 9973.
1894
1895       The  name  can then be used in option definitions, as described earlier
1896       in this document.  For example:
1897
1898       option space SUNW code width 1 length width 1 hash size 3;
1899       option SUNW.server-address code 2 = ip-address;
1900       option SUNW.server-name code 3 = text;
1901       option SUNW.root-path code 4 = text;
1902
1903       option space ISC code width 1 length width 1 hash size 3;
1904       option ISC.sample code 1 = text;
1905       option vendor.ISC code 2495 = encapsulate vivso-sample;
1906       option vendor-class.ISC code 2495 = text;
1907
1908       option ISC.sample "configuration text here";
1909       option vendor-class.ISC "vendor class here";
1910
1911       option space docsis code width 2 length width 2 hash size 17;
1912       option docsis.tftp-servers code 32 = array of ip6-address;
1913       option docsis.cablelabs-configuration-file code 33 = text;
1914       option docsis.cablelabs-syslog-servers code 34 = array of ip6-address;
1915       option docsis.device-id code 36 = string;
1916       option docsis.time-servers code 37 = array of ip6-address;
1917       option docsis.time-offset code 38 = signed integer 32;
1918       option vsio.docsis code 4491 = encapsulate docsis;
1919
1920       Once you have defined an option space and the format of  some  options,
1921       you can set up scopes that define values for those options, and you can
1922       say when to use them.  For example, suppose you want to handle two dif‐
1923       ferent  classes of clients.  Using the option space definition shown in
1924       the previous example, you can send different option values to different
1925       clients  based  on  the vendor-class-identifier option that the clients
1926       send, as follows:
1927
1928       class "vendor-classes" {
1929         match option vendor-class-identifier;
1930       }
1931
1932       subclass "vendor-classes" "SUNW.Ultra-5_10" {
1933         vendor-option-space SUNW;
1934         option SUNW.root-path "/export/root/sparc";
1935       }
1936
1937       subclass "vendor-classes" "SUNW.i86pc" {
1938         vendor-option-space SUNW;
1939         option SUNW.root-path "/export/root/i86pc";
1940       }
1941
1942       option SUNW.server-address 172.17.65.1;
1943       option SUNW.server-name "sundhcp-server17-1";
1944
1945       option vivso-sample.sample "Hello world!";
1946
1947       option docsis.tftp-servers ::1;
1948
1949
1950       As you can see in the preceding example, regular scoping  rules  apply,
1951       so  you can define values that are global in the global scope, and only
1952       define values that are specific to a  particular  class  in  the  local
1953       scope.   The  vendor-option-space  declaration tells the DHCP server to
1954       use options in the SUNW option space to construct  the  DHCPv4  vendor-
1955       encapsulated-options option.  This is a limitation of that option - the
1956       DHCPv4 VIVSO and the DHCPv6 VSIO options can have multiple vendor defi‐
1957       nitions all at once (even transmitted to the same client), so it is not
1958       necessary to configure this.
1959

SEE ALSO

1961       dhcpd.conf(5),   dhcpd.leases(5),    dhclient.conf(5),    dhcp-eval(5),
1962       dhcpd(8), dhclient(8), RFC2132, RFC2131, RFC3046, RFC3315.
1963

AUTHOR

1965       Information   about   Internet  Systems  Consortium  can  be  found  at
1966       https://www.isc.org.
1967
1968
1969
1970                                                               dhcp-options(5)
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