3 <!-- $Id: References.xml,v 1.4.24.3 2011-07-05 16:57:20 sar Exp $ -->
5 <?rfc private="ISC-DHCP-REFERENCES" ?>
10 <?rfc subcompact="no"?>
11 <?rfc tocompact="no"?>
14 <!DOCTYPE rfc SYSTEM 'rfc2629bis.dtd' [
15 <!ENTITY rfc760 PUBLIC ''
16 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0760.xml'>
17 <!ENTITY rfc768 PUBLIC ''
18 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0768.xml'>
19 <!ENTITY rfc894 PUBLIC ''
20 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0894.xml'>
21 <!ENTITY rfc951 PUBLIC ''
22 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0951.xml'>
23 <!ENTITY rfc1035 PUBLIC ''
24 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1035.xml'>
25 <!ENTITY rfc1188 PUBLIC ''
26 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1188.xml'>
27 <!ENTITY rfc1542 PUBLIC ''
28 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1542.xml'>
29 <!ENTITY rfc2131 PUBLIC ''
30 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2131.xml'>
31 <!ENTITY rfc2132 PUBLIC ''
32 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2132.xml'>
33 <!ENTITY rfc2241 PUBLIC ''
34 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2241.xml'>
35 <!ENTITY rfc2242 PUBLIC ''
36 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2242.xml'>
37 <!ENTITY rfc2485 PUBLIC ''
38 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2485.xml'>
39 <!ENTITY rfc2610 PUBLIC ''
40 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2610.xml'>
41 <!ENTITY rfc2937 PUBLIC ''
42 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2937.xml'>
43 <!ENTITY rfc2939 PUBLIC ''
44 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2939.xml'>
45 <!ENTITY rfc3004 PUBLIC ''
46 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3004.xml'>
47 <!ENTITY rfc3011 PUBLIC ''
48 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3011.xml'>
49 <!ENTITY rfc3046 PUBLIC ''
50 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3046.xml'>
51 <!ENTITY rfc3074 PUBLIC ''
52 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3074.xml'>
53 <!ENTITY rfc3256 PUBLIC ''
54 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3256.xml'>
55 <!ENTITY rfc3315 PUBLIC ''
56 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3315.xml'>
57 <!ENTITY rfc3319 PUBLIC ''
58 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3319.xml'>
59 <!ENTITY rfc3396 PUBLIC ''
60 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3396.xml'>
61 <!ENTITY rfc3397 PUBLIC ''
62 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3397.xml'>
63 <!ENTITY rfc3527 PUBLIC ''
64 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3527.xml'>
65 <!ENTITY rfc3633 PUBLIC ''
66 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3633.xml'>
67 <!ENTITY rfc3646 PUBLIC ''
68 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3646.xml'>
69 <!ENTITY rfc3679 PUBLIC ''
70 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3679.xml'>
71 <!ENTITY rfc3898 PUBLIC ''
72 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3898.xml'>
73 <!ENTITY rfc3925 PUBLIC ''
74 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3925.xml'>
75 <!ENTITY rfc3942 PUBLIC ''
76 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3942.xml'>
77 <!ENTITY rfc4075 PUBLIC ''
78 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4075.xml'>
79 <!ENTITY rfc4242 PUBLIC ''
80 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4242.xml'>
81 <!ENTITY rfc4361 PUBLIC ''
82 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4361.xml'>
83 <!ENTITY rfc4388 PUBLIC ''
84 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4388.xml'>
85 <!ENTITY rfc4580 PUBLIC ''
86 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4580.xml'>
87 <!ENTITY rfc4649 PUBLIC ''
88 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4649.xml'>
89 <!ENTITY rfc4701 PUBLIC ''
90 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4701.xml'>
91 <!ENTITY rfc4702 PUBLIC ''
92 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4702.xml'>
93 <!ENTITY rfc4703 PUBLIC ''
94 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4703.xml'>
101 <title>ISC DHCP References Collection</title>
103 <author initials="D.H." surname="Hankins" fullname="David W. Hankins">
104 <organization abbrev="ISC">Internet Systems Consortium,
110 <street>950 Charter Street</street>
111 <city>Redwood City</city>
118 <author initials="T." surname="Mrugalski" fullname="Tomasz Mrugalski">
119 <organization abbrev="ISC">Internet Systems Consortium,
125 <street>950 Charter Street</street>
126 <city>Redwood City</city>
131 <phone>+1 650 423 1345</phone>
132 <email>Tomasz_Mrugalski@isc.org</email>
136 <date day="20" month="May" year="2011"/>
138 <keyword>ISC</keyword>
139 <keyword>DHCP</keyword>
140 <keyword>Reference Implementation</keyword>
143 <t>This document describes a collection of reference material
144 to which ISC DHCP has been implemented as well as a more
145 complete listing of references for DHCP and DHCPv6 protocols.</t>
148 <note title="Copyright Notice">
149 <t>Copyright (c) 2006-2007,2009,2011 by Internet Systems
150 Consortium, Inc. ("ISC")</t>
152 <t>Permission to use, copy, modify, and distribute this software for
153 any purpose with or without fee is hereby granted, provided that the
154 above copyright notice and this permission notice appear in all
157 <t>THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
158 WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
159 MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
160 ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
161 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
162 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
163 OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.</t>
169 <section title="Introduction">
170 <t>As a little historical anecdote, ISC DHCP once packaged all the
171 relevant RFCs and standards documents along with the software
172 package. Until one day when a voice was heard from one of the
173 many fine institutions that build and distribute this software...
174 they took issue with the IETF's copyright on the RFC's. It
175 seems the IETF's copyrights don't allow modification of RFC's
176 (except for translation purposes).</t>
178 <t>Our main purpose in providing the RFCs is to aid in
179 documentation, but since RFCs are now available widely from many
180 points of distribution on the Internet, there is no real need to
181 provide the documents themselves. So, this document has been
182 created in their stead, to list the various IETF RFCs one might
183 want to read, and to comment on how well (or poorly) we have
184 managed to implement them.</t>
187 <section title="Definition: Reference Implementation">
188 <t>ISC DHCP, much like its other cousins in ISC software, is
189 self-described as a 'Reference Implementation.' There has been
190 a great deal of confusion about this term. Some people seem to
191 think that this term applies to any software that once passed
192 a piece of reference material on its way to market (but may do
193 quite a lot of things that aren't described in any reference, or
194 may choose to ignore the reference it saw entirely). Other folks
195 get confused by the word 'reference' and understand that to mean
196 that there is some special status applied to the software - that
197 the software itself is the reference by which all other software
198 is measured. Something along the lines of being "The DHCP
199 Protocol's Reference Clock," it is supposed.</t>
201 <t>The truth is actually quite a lot simpler. Reference
202 implementations are software packages which were written
203 to behave precisely as appears in reference material. They
204 are written "to match reference."</t>
206 <t>If the software has a behaviour that manifests itself
207 externally (whether it be something as simple as the 'wire
208 format' or something higher level, such as a complicated
209 behaviour that arises from multiple message exchanges), that
210 behaviour must be found in a reference document.</t>
212 <t>Anything else is a bug, the only question is whether the
213 bug is in reference or software (failing to implement the
219 <list style="symbols">
220 <t>To produce new externally-visible behaviour, one must first
221 provide a reference.</t>
223 <t>Before changing externally visible behaviour to work around
224 simple incompatibilities in any other implementation, one must
225 first provide a reference.</t>
229 <t>That is the lofty goal, at any rate. It's well understood that,
230 especially because the ISC DHCP Software package has not always been
231 held to this standard (but not entirely due to it), there are many
232 non-referenced behaviours within ISC DHCP.</t>
234 <t>The primary goal of reference implementation is to prove the
235 reference material. If the reference material is good, then you
236 should be able to sit down and write a program that implements the
237 reference, to the word, and come to an implementation that
238 is distinguishable from others in the details, but not in the
239 facts of operating the protocol. This means that there is no
240 need for 'special knowledge' to work around arcane problems that
241 were left undocumented. No secret handshakes need to be learned
242 to be imparted with the necessary "real documentation".</t>
244 <t>Also, by accepting only reference as the guidebook for ISC
245 DHCP's software implementation, anyone who can make an impact on
246 the color texture or form of that reference has a (somewhat
247 indirect) voice in ISC DHCP's software design. As the IETF RFC's
248 have been selected as the source of reference, that means everyone
249 on the Internet with the will to participate has a say.</t>
252 <section title="Low Layer References">
253 <t>It may surprise you to realize that ISC DHCP implements 802.1
254 'Ethernet' framing, Token Ring, and FDDI. In order to bridge the
255 gap there between these physical and DHCP layers, it must also
256 implement IP and UDP framing.</t>
258 <t>The reason for this stems from Unix systems' handling of BSD
259 sockets (the general way one might engage in transmission of UDP
260 packets) on unconfigured interfaces, or even the handling of
261 broadcast addressing on configured interfaces.</t>
263 <t>There are a few things that DHCP servers, relays, and clients all
264 need to do in order to speak the DHCP protocol in strict compliance
265 with <xref target="RFC2131"/>.
267 <list style="numbers">
268 <t>Transmit a UDP packet from IP:0.0.0.0 Ethernet:Self, destined to
269 IP:255.255.255.255 LinkLayer:Broadcast on an unconfigured (no IP
270 address yet) interface.</t>
272 <t>Receive a UDP packet from IP:remote-system LinkLayer:remote-system,
273 destined to IP:255.255.255.255 LinkLayer:Broadcast, again on an
274 unconfigured interface.</t>
276 <t>Transmit a UDP packet from IP:Self, Ethernet:Self, destined to
277 IP:remote-system LinkLayer:remote-system, without transmitting a
280 <t>And of course the simple case, a regular IP unicast that is
281 routed via the usual means (so it may be direct to a local system,
282 with ARP providing the glue, or it may be to a remote system via
283 one or more routers as normal). In this case, the interfaces are
284 always configured.</t>
287 <t>The above isn't as simple as it sounds on a regular BSD socket.
288 Many unix implementations will transmit broadcasts not to
289 255.255.255.255, but to x.y.z.255 (where x.y.z is the system's local
290 subnet). Such packets are not received by several known DHCP client
291 implementations - and it's not their fault, <xref target="RFC2131"/>
292 very explicitly demands that these packets' IP destination
293 addresses be set to 255.255.255.255.</t>
295 <t>Receiving packets sent to 255.255.255.255 isn't a problem on most
296 modern unixes...so long as the interface is configured. When there
297 is no IPv4 address on the interface, things become much more murky.</t>
299 <t>So, for this convoluted and unfortunate state of affairs in the
300 unix systems of the day ISC DHCP was manufactured, in order to do
301 what it needs not only to implement the reference but to interoperate
302 with other implementations, the software must create some form of
303 raw socket to operate on.</t>
305 <t>What it actually does is create, for each interface detected on
306 the system, a Berkeley Packet Filter socket (or equivalent), and
307 program it with a filter that brings in only DHCP packets. A
308 "fallback" UDP Berkeley socket is generally also created, a single
309 one no matter how many interfaces. Should the software need to
310 transmit a contrived packet to the local network the packet is
311 formed piece by piece and transmitted via the BPF socket. Hence
312 the need to implement many forms of Link Layer framing and above.
313 The software gets away with not having to implement IP routing
314 tables as well by simply utilizing the aforementioned 'fallback'
315 UDP socket when unicasting between two configured systems is
318 <t>Modern unixes have opened up some facilities that diminish how
319 much of this sort of nefarious kludgery is necessary, but have not
320 found the state of affairs absolutely resolved. In particular,
321 one might now unicast without ARP by inserting an entry into the
322 ARP cache prior to transmitting. Unconfigured interfaces remain
323 the sticking point, however...on virtually no modern unixes is
324 it possible to receive broadcast packets unless a local IPv4
325 address has been configured, unless it is done with raw sockets.</t>
327 <section title="Ethernet Protocol References">
328 <t>ISC DHCP Implements Ethernet Version 2 ("DIX"), which is a variant
329 of IEEE 802.2. No good reference of this framing is known to exist
330 at this time, but it is vaguely described in <xref target="RFC0894"/>
331 see the section titled "Packet format"), and
332 the following URL is also thought to be useful.</t>
334 <t><eref target="http://en.wikipedia.org/wiki/DIX_Ethernet">http://en.wikipedia.org/wiki/DIX_Ethernet</eref></t>
337 <section title="Token Ring Protocol References">
338 <t>IEEE 802.5 defines the Token Ring framing format used by ISC
342 <section title="FDDI Protocol References">
343 <t><xref target="RFC1188"/> is the most helpful
344 reference ISC DHCP has used to form FDDI packets.</t>
347 <section title="Internet Protocol Version 4 References">
348 <t><xref target="RFC0760">RFC760</xref> fundamentally defines the
349 bare IPv4 protocol which ISC DHCP implements.</t>
352 <section title="Unicast Datagram Protocol References">
353 <t><xref target="RFC0768">RFC768</xref> defines the User Datagram
354 Protocol that ultimately carries the DHCP or BOOTP protocol. The
355 destination DHCP server port is 67, the client port is 68. Source
356 ports are irrelevant.</t>
360 <section title="BOOTP Protocol References">
361 <t>The DHCP Protocol is strange among protocols in that it is
362 grafted over the top of another protocol - BOOTP (but we don't
363 call it "DHCP over BOOTP" like we do, say "TCP over IP"). BOOTP
364 and DHCP share UDP packet formats - DHCP is merely a conventional
365 use of both BOOTP header fields and the trailing 'options' space.</t>
367 <t>The ISC DHCP server supports BOOTP clients conforming to
368 <xref target="RFC0951">RFC951</xref> and <xref target="RFC1542">
372 <section title="DHCPv4 Protocol References">
373 <section title="DHCPv4 Protocol">
374 <t>"The DHCP[v4] Protocol" is not defined in a single document. The
375 following collection of references of what ISC DHCP terms "The
376 DHCPv4 Protocol".</t>
378 <section title="Core Protocol References">
379 <t><xref target="RFC2131">RFC2131</xref> defines the protocol format
380 and procedures. ISC DHCP is not known to diverge from this document
381 in any way. There are, however, a few points on which different
382 implementations have arisen out of vagueries in the document.
383 DHCP Clients exist which, at one time, present themselves as using
384 a Client Identifier Option which is equal to the client's hardware
385 address. Later, the client transmits DHCP packets with no Client
386 Identifier Option present - essentially identifying themselves using
387 the hardware address. Some DHCP Servers have been developed which
388 identify this client as a single client. ISC has interpreted
389 RFC2131 to indicate that these clients must be treated as two
390 separate entities (and hence two, separate addresses). Client
391 behaviour (Embedded Windows products) has developed that relies on
392 the former implementation, and hence is incompatible with the
393 latter. Also, RFC2131 demands explicitly that some header fields
394 be zeroed upon certain message types. The ISC DHCP Server instead
395 copies many of these fields from the packet received from the client
396 or relay, which may not be zero. It is not known if there is a good
397 reason for this that has not been documented.</t>
399 <t><xref target="RFC2132">RFC2132</xref> defines the initial set of
400 DHCP Options and provides a great deal of guidance on how to go about
401 formatting and processing options. The document unfortunately
402 waffles to a great extent about the NULL termination of DHCP Options,
403 and some DHCP Clients (Windows 95) have been implemented that rely
404 upon DHCP Options containing text strings to be NULL-terminated (or
405 else they crash). So, ISC DHCP detects if clients null-terminate the
406 host-name option and, if so, null terminates any text options it
407 transmits to the client. It also removes NULL termination from any
408 known text option it receives prior to any other processing.</t>
412 <section title="DHCPv4 Option References">
413 <t><xref target="RFC2241">RFC2241</xref> defines options for
414 Novell Directory Services.</t>
416 <t><xref target="RFC2242">RFC2242</xref> defines an encapsulated
417 option space for NWIP configuration.</t>
419 <t><xref target="RFC2485">RFC2485</xref> defines the Open Group's
422 <t><xref target="RFC2610">RFC2610</xref> defines options for
423 the Service Location Protocol (SLP).</t>
425 <t><xref target="RFC2937">RFC2937</xref> defines the Name Service
426 Search Option (not to be confused with the domain-search option).
427 The Name Service Search Option allows eg nsswitch.conf to be
428 reconfigured via dhcp. The ISC DHCP server implements this option,
429 and the ISC DHCP client is compatible...but does not by default
430 install this option's value. One would need to make their relevant
431 dhclient-script process this option in a way that is suitable for
434 <t><xref target="RFC3004">RFC3004</xref> defines the User-Class
435 option. Note carefully that ISC DHCP currently does not implement
436 to this reference, but has (inexplicably) selected an incompatible
437 format: a plain text string.</t>
439 <t><xref target="RFC3011">RFC3011</xref> defines the Subnet-Selection
440 plain DHCPv4 option. Do not confuse this option with the relay agent
441 "link selection" sub-option, although their behaviour is
444 <t><xref target="RFC3396">RFC3396</xref> documents both how long
445 options may be encoded in DHCPv4 packets, and also how multiple
446 instances of the same option code within a DHCPv4 packet will be
447 decoded by receivers.</t>
449 <t><xref target="RFC3397">RFC3397</xref> documents the Domain-Search
450 Option, which allows the configuration of the /etc/resolv.conf
451 'search' parameter in a way that is <xref target="RFC1035">RFC1035
452 </xref> wire format compatible (in fact, it uses the RFC1035 wire
453 format). ISC DHCP has both client and server support, and supports
454 RFC1035 name compression.</t>
456 <t><xref target="RFC3679">RFC3679</xref> documents a number of
457 options that were documented earlier in history, but were not
460 <t><xref target="RFC3925">RFC3925</xref> documents a pair of
461 Enterprise-ID delimited option spaces for vendors to use in order
462 to inform servers of their "vendor class" (sort of like 'uname'
463 or 'who and what am I'), and a means to deliver vendor-specific
464 and vendor-documented option codes and values.</t>
466 <t><xref target="RFC3942">RFC3942</xref> redefined the 'site local'
469 <t><xref target="RFC4280" /> defines two BCMS server options
470 for each protocol family.</t>
472 <t><xref target="RFC4388">RFC4388</xref> defined the DHCPv4
473 LEASEQUERY message type and a number of suitable response messages,
474 for the purpose of sharing information about DHCP served addresses
477 <section title="Relay Agent Information Option Options">
478 <t><xref target="RFC3046">RFC3046</xref> defines the Relay Agent
479 Information Option and provides a number of sub-option
482 <t><xref target="RFC3256">RFC3256</xref> defines the DOCSIS Device
483 Class sub-option.</t>
485 <t><xref target="RFC3527">RFC3527</xref> defines the Link Selection
490 <section title="Dynamic DNS Updates References">
491 <t>The collection of documents that describe the standards-based
492 method to update dns names of DHCP clients starts most easily
493 with <xref target="RFC4703">RFC4703</xref> to define the overall
494 architecture, travels through RFCs <xref target="RFC4702">4702</xref>
495 and <xref target="RFC4704">4704</xref> to describe the DHCPv4 and
496 DHCPv6 FQDN options (to carry the client name), and ends up at
497 <xref target="RFC4701">RFC4701</xref> which describes the DHCID
498 RR used in DNS to perform a kind of atomic locking.</t>
500 <t>ISC DHCP adopted early versions of these documents, and has not
501 yet synchronized with the final standards versions.</t>
503 <t>For RFCs 4702 and 4704, the 'N' bit is not yet supported. The
504 result is that it is always set zero, and is ignored if set.</t>
506 <t>For RFC4701, which is used to match client identities with names
507 in the DNS as part of name conflict resolution. Note that ISC DHCP's
508 implementation of DHCIDs vary wildly from this specification.
509 First, ISC DHCP uses a TXT record in which the contents are stored
510 in hexadecimal. Second, there is a flaw in the selection of the
511 'Identifier Type', which results in a completely different value
512 being selected than was defined in an older revision of this
513 document...also this field is one byte prior to hexadecimal
514 encoding rather than two. Third, ISC DHCP does not use a digest
515 type code. Rather, all values for such TXT records are reached
516 via an MD5 sum. In short, nothing is compatible, but the
517 principle of the TXT record is the same as the standard DHCID
518 record. However, for DHCPv6 FQDN, we do use DHCID type code '2',
519 as no other value really makes sense in our context.</t>
522 <section title="Experimental: Failover References">
523 <t>The Failover Protocol defines means by which two DHCP Servers
524 can share all the relevant information about leases granted to
525 DHCP clients on given networks, so that one of the two servers may
526 fail and be survived by a server that can act responsibly.</t>
528 <t>Unfortunately it has been quite some years (2003) since the last
529 time this document was edited, and the authors no longer show any
530 interest in fielding comments or improving the document.</t>
532 <t>The status of this protocol is very unsure, but ISC's
533 implementation of it has proven stable and suitable for use in
534 sizable production environments.</t>
536 <t><xref target="draft-failover">draft-ietf-dhc-failover-12.txt</xref>
537 describes the Failover Protocol. In addition to what is described
538 in this document, ISC DHCP has elected to make some experimental
539 changes that may be revoked in a future version of ISC DHCP (if the
540 draft authors do not adopt the new behaviour). Specifically, ISC
541 DHCP's POOLREQ behaviour differs substantially from what is
542 documented in the draft, and the server also implements a form of
543 'MAC Address Affinity' which is not described in the failover
544 document. The full nature of these changes have been described on
545 the IETF DHC WG mailing list (which has archives), and also in ISC
546 DHCP's manual pages. Also note that although this document
547 references a RECOVER-WAIT state, it does not document a protocol
548 number assignment for this state. As a consequence, ISC DHCP has
549 elected to use the value 254.</t>
551 <t> An optimization described in the failover protocol draft
552 is included since 4.2.0a1. It permits a DHCP server
553 operating in communications-interrupted state to 'rewind' a
554 lease to the state most recently transmitted to its peer,
555 greatly increasing a server's endurance in
556 communications-interrupted. This is supported using a new
557 'rewind state' record on the dhcpd.leases entry for each
561 <t><xref target="RFC3074" /> describes the Load Balancing
562 Algorithm (LBA) that ISC DHCP uses in concert with the Failover
563 protocol. Note that versions 3.0.* are known to misimplement the
564 hash algorithm (it will only use the low 4 bits of every byte of
565 the hash bucket array).</t>
569 <section title="DHCP Procedures">
570 <t><xref target="RFC2939" /> explains how to go about
571 obtaining a new DHCP Option code assignment.</t>
576 <section title="DHCPv6 Protocol References">
578 <section title="DHCPv6 Protocol References">
579 <t>For now there is only one document that specifies the base
580 of the DHCPv6 protocol (there have been no updates yet),
581 <xref target="RFC3315"/>.</t>
583 <t>Support for DHCPv6 was first added in version 4.0.0. The server
584 and client support only IA_NA. While the server does support multiple
585 IA_NAs within one packet from the client, our client only supports
586 sending one. There is no relay support.</t>
588 <t>DHCPv6 introduces some new and uncomfortable ideas to the common
589 software library.</t>
592 <list style="numbers">
593 <t>Options sometimes may appear multiple times. The common
594 library used to treat all appearance of multiple options as
595 specified in RFC2131 - to be concatenated. DHCPv6 options
596 may sometimes appear multiple times (such as with IA_NA or
597 IAADDR), but often must not. As of 4.2.1-P1, multiple IA_NA, IA_PD
598 or IA_TA are not supported.</t>
600 <t>The same option space appears in DHCPv6 packets multiple times.
601 If the packet was got via a relay, then the client's packet is
602 stored to an option within the relay's packet...if there were two
603 relays, this recurses. At each of these steps, the root "DHCPv6
604 option space" is used. Further, a client packet may contain an
605 IA_NA, which may contain an IAADDR - but really, in an abstract
606 sense, this is again re-encapsulation of the DHCPv6 option space
607 beneath options it also contains.</t>
611 <t>Precisely how to correctly support the above conundrums has not
612 quite yet been settled, so support is incomplete.</t>
615 <section title="DHCPv6 Options References">
616 <t><xref target="RFC3319"/> defines the SIP server
617 options for DHCPv6.</t>
619 <t><xref target="RFC3646"/> documents the DHCPv6
620 name-servers and domain-search options.</t>
622 <t><xref target="RFC3633"/> documents the Identity
623 Association Prefix Delegation for DHCPv6, which is included
624 here for protocol wire reference, but which is not supported
627 <t><xref target="RFC3898"/> documents four NIS options
628 for delivering NIS servers and domain information in DHCPv6.</t>
630 <t><xref target="RFC4075"/> defines the DHCPv6 SNTP
633 <t><xref target="RFC4242"/> defines the Information
634 Refresh Time option, which advises DHCPv6 Information-Request
635 clients to return for updated information.</t>
637 <t><xref target="RFC4280"/> defines two BCMS server options
638 for each protocol family.</t>
640 <t><xref target="RFC4580"/> defines a DHCPv6
641 subscriber-id option, which is similar in principle to the DHCPv4
642 relay agent option of the same name.</t>
644 <t><xref target="RFC4649"/> defines a DHCPv6 remote-id
645 option, which is similar in principle to the DHCPv4 relay agent
654 <references title="Published DHCPv4 References">
667 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2563'?>
669 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2855'?>
676 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3118'?>
677 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3203'?>
679 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3361'?>
682 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3442'?>
683 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3456'?>
684 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3495'?>
686 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3594'?>
687 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3634'?>
689 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3825'?>
692 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3993'?>
693 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4014'?>
694 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4030'?>
695 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4039'?>
696 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4174'?>
697 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4243'?>
700 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4390'?>
701 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4436'?>
702 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4701'?>
703 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4702'?>
704 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4703'?>
705 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5010'?>
706 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5071'?>
707 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5107'?>
708 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5192'?>
709 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5223'?>
710 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5859'?>
711 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5969'?>
713 <reference anchor='draft-failover'>
715 <title>DHCP Failover Protocol</title>
716 <author initials='R.' surname='Droms' fullname='Ralph Droms'>
717 <organization abbrev='Cisco'>Cisco Systems</organization>
719 <date month='March' year='2003'/>
721 <format type="TXT" octets="312151" target="https://www.isc.org/sw/dhcp/drafts/draft-ietf-dhc-failover-12.txt"/>
724 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-dhcpv4-relay-encapsulation-00.xml'?>
725 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-dhcpv4-bulk-leasequery-03.xml'?>
726 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-leasequery-by-remote-id-09.xml'?>
727 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-relay-id-suboption-07.xml'?>
728 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-mip6-hiopt-17.xml'?>
732 <references title="Published Common (DHCPv4/DHCPv6) References">
733 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4280'?>
734 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4477'?>
735 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4578'?>
736 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4776'?>
737 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4833'?>
738 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5417'?>
739 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5678'?>
740 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5908'?>
741 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5970'?>
742 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5986'?>
743 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-vpn-option-12.xml'?>
747 <references title="Published DHCPv6 References">
753 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3736'?>
756 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4076'?>
760 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4704'?>
761 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4994'?>
762 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5007'?>
763 <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5460'?>
764 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-mif-dhcpv6-route-option'?>
765 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-dhc-dhcpv6-ldra'?>
766 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-dhc-dhcpv6-relay-supplied-options'?>
767 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-pd-exclude-01.xml'?>
768 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-secure-dhcpv6-02.xml'?>
769 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-mext-nemo-pd'?>
770 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-duid-uuid-03.xml'?>
771 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-softwire-ds-lite-tunnel-option-10.xml'?>
772 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-mif-dns-server-selection-01.xml'?>
773 <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-geopriv-rfc3825bis-17.xml'?>
775 <reference anchor='draft-addr-params'>
777 <title>Address Parameters Option for DHCPv6</title>
778 <author initials='T.' surname='Mrugalski' fullname='Mrugalski'>
779 <organization abbrev='Cisco'>Gdansk University of Technology</organization>
781 <date month='April' year='2007'/>
783 <format type="TXT" target="http://klub.com.pl/dhcpv6/doc/draft-mrugalski-addropts-XX-2007-04-17.txt"/>