summaryrefslogtreecommitdiff
path: root/doc/References.xml
blob: 7f310ff8ae5a6816862b0023712f82487fbc2dc8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
<?xml version='1.0' ?>

<!-- $Id: References.xml,v 1.8 2012/01/05 00:03:17 sar Exp $ -->

<?rfc private="ISC-DHCP-REFERENCES" ?>

<?rfc toc="yes"?>

<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc tocompact="no"?>
<?rfc symrefs="yes"?>

<!DOCTYPE rfc SYSTEM 'rfc2629bis.dtd' [
  <!ENTITY rfc760 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0760.xml'>
  <!ENTITY rfc768 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0768.xml'>
  <!ENTITY rfc894 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0894.xml'>
  <!ENTITY rfc951 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.0951.xml'>
  <!ENTITY rfc1035 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1035.xml'>
  <!ENTITY rfc1188 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1188.xml'>
  <!ENTITY rfc1542 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.1542.xml'>
  <!ENTITY rfc2131 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2131.xml'>
  <!ENTITY rfc2132 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2132.xml'>
  <!ENTITY rfc2241 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2241.xml'>
  <!ENTITY rfc2242 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2242.xml'>
  <!ENTITY rfc2485 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2485.xml'>
  <!ENTITY rfc2610 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2610.xml'>
  <!ENTITY rfc2937 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2937.xml'>
  <!ENTITY rfc2939 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2939.xml'>
  <!ENTITY rfc3004 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3004.xml'>
  <!ENTITY rfc3011 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3011.xml'>
  <!ENTITY rfc3046 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3046.xml'>
  <!ENTITY rfc3074 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3074.xml'>
  <!ENTITY rfc3256 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3256.xml'>
  <!ENTITY rfc3315 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3315.xml'>
  <!ENTITY rfc3319 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3319.xml'>
  <!ENTITY rfc3396 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3396.xml'>
  <!ENTITY rfc3397 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3397.xml'>
  <!ENTITY rfc3527 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3527.xml'>
  <!ENTITY rfc3633 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3633.xml'>
  <!ENTITY rfc3646 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3646.xml'>
  <!ENTITY rfc3679 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3679.xml'>
  <!ENTITY rfc3898 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3898.xml'>
  <!ENTITY rfc3925 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3925.xml'>
  <!ENTITY rfc3942 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3942.xml'>
  <!ENTITY rfc4075 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4075.xml'>
  <!ENTITY rfc4242 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4242.xml'>
  <!ENTITY rfc4361 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4361.xml'>
  <!ENTITY rfc4388 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4388.xml'>
  <!ENTITY rfc4580 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4580.xml'>
  <!ENTITY rfc4649 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4649.xml'>
  <!ENTITY rfc4701 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4701.xml'>
  <!ENTITY rfc4702 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4702.xml'>
  <!ENTITY rfc4703 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4703.xml'>
  <!ENTITY rfc5453 PUBLIC ''
	'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5453.xml'>
  ]>



<rfc ipr="none">
  <front>
    <title>ISC DHCP References Collection</title>

    <author initials="D.H." surname="Hankins" fullname="David W. Hankins">
      <organization abbrev="ISC">Internet Systems Consortium,
				 Inc.
      </organization>

      <address>
	<postal>
	  <street>PO Box 360</street>
	  <city>Newmarket</city>
	  <region>NH</region>
	  <code>03857</code>
	  <country>USA</country>
	</postal>
      </address>
    </author>

    <author initials="T." surname="Mrugalski" fullname="Tomasz Mrugalski">
      <organization abbrev="ISC">Internet Systems Consortium,
				 Inc.
      </organization>

      <address>
	<postal>
	  <street>PO Box 360</street>
	  <city>Newmarket</city>
	  <region>NH</region>
	  <code>03857</code>
	  <country>USA</country>
	</postal>
      </address>
    </author>

    <date day="04" month="January" year="2012"/>

    <keyword>ISC</keyword>
    <keyword>DHCP</keyword>
    <keyword>Reference Implementation</keyword>

    <abstract>
	<t>This document describes a collection of reference material
	to which ISC DHCP has been implemented as well as a more
	complete listing of references for DHCP and DHCPv6 protocols.</t>
    </abstract>

    <note title="Copyright Notice">
	<t>Copyright (C) 2006-2022 Internet Systems
	  Consortium, Inc. ("ISC")</t>

	<t>This Source Code Form is subject to the terms of the Mozilla Public
	License, v. 2.0. If a copy of the MPL was not distributed with this
	file, You can obtain one at http://mozilla.org/MPL/2.0/.
	</t>

	<t>THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
	WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
	ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
	ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
	OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.</t>
    </note>

  </front>

  <middle>
    <section title="Introduction">
	<t>As a little historical anecdote, ISC DHCP once packaged all the
	relevant RFCs and standards documents along with the software
	package.  Until one day when a voice was heard from one of the
	many fine institutions that build and distribute this software...
	they took issue with the IETF's copyright on the RFC's.  It
	seems the IETF's copyrights don't allow modification of RFC's
	(except for translation purposes).</t>

	<t>Our main purpose in providing the RFCs is to aid in
	documentation, but since RFCs are now available widely from many
	points of distribution on the Internet, there is no real need to
	provide the documents themselves.  So, this document has been
	created in their stead, to list the various IETF RFCs one might
	want to read, and to comment on how well (or poorly) we have
	managed to implement them.</t>
    </section>

    <section title="Definition: Reference Implementation">
	<t>ISC DHCP, much like its other cousins in ISC software, is
	self-described as a 'Reference Implementation.'  There has been
	a great deal of confusion about this term.  Some people seem to
	think that this term applies to any software that once passed
	a piece of reference material on its way to market (but may do
	quite a lot of things that aren't described in any reference, or
	may choose to ignore the reference it saw entirely).  Other folks
	get confused by the word 'reference' and understand that to mean
	that there is some special status applied to the software - that
	the software itself is the reference by which all other software
	is measured.  Something along the lines of being "The DHCP
	Protocol's Reference Clock," it is supposed.</t>

	<t>The truth is actually quite a lot simpler.  Reference
	implementations are software packages which were written
	to behave precisely as appears in reference material.  They
	are written "to match reference."</t>

	<t>If the software has a behaviour that manifests itself
	externally (whether it be something as simple as the 'wire
	format' or something higher level, such as a complicated
	behaviour that arises from multiple message exchanges), that
	behaviour must be found in a reference document.</t>

	<t>Anything else is a bug, the only question is whether the
	bug is in reference or software (failing to implement the
	reference).</t>

	<t>This means:</t>

	<t>
      <list style="symbols">
	<t>To produce new externally-visible behaviour, one must first
	provide a reference.</t>

	<t>Before changing externally visible behaviour to work around
	simple incompatibilities in any other implementation, one must
	first provide a reference.</t>
      </list>
	</t>

	<t>That is the lofty goal, at any rate.  It's well understood that,
	especially because the ISC DHCP Software package has not always been
	held to this standard (but not entirely due to it), there are many
	non-referenced behaviours within ISC DHCP.</t>

	<t>The primary goal of reference implementation is to prove the
	reference material.  If the reference material is good, then you
	should be able to sit down and write a program that implements the
	reference, to the word, and come to an implementation that
	is distinguishable from others in the details, but not in the
	facts of operating the protocol.  This means that there is no
	need for 'special knowledge' to work around arcane problems that
	were left undocumented.  No secret handshakes need to be learned
	to be imparted with the necessary "real documentation".</t>

	<t>Also, by accepting only reference as the guidebook for ISC
	DHCP's software implementation, anyone who can make an impact on
	the color texture or form of that reference has a (somewhat
	indirect) voice in ISC DHCP's software design.  As the IETF RFC's
	have been selected as the source of reference, that means everyone
	on the Internet with the will to participate has a say.</t>
    </section>

    <section title="Low Layer References">
	<t>It may surprise you to realize that ISC DHCP implements 802.1
	'Ethernet' framing, Token Ring, and FDDI.  In order to bridge the
	gap there between these physical and DHCP layers, it must also
	implement IP and UDP framing.</t>

	<t>The reason for this stems from Unix systems' handling of BSD
	sockets (the general way one might engage in transmission of UDP
	packets) on unconfigured interfaces, or even the handling of
	broadcast addressing on configured interfaces.</t>

	<t>There are a few things that DHCP servers, relays, and clients all
	need to do in order to speak the DHCP protocol in strict compliance
	with <xref target="RFC2131"/>.

      <list style="numbers">
	<t>Transmit a UDP packet from IP:0.0.0.0 Ethernet:Self, destined to
	IP:255.255.255.255 LinkLayer:Broadcast on an unconfigured (no IP
	address yet) interface.</t>

	<t>Receive a UDP packet from IP:remote-system LinkLayer:remote-system,
	destined to IP:255.255.255.255 LinkLayer:Broadcast, again on an
	unconfigured interface.</t>

	<t>Transmit a UDP packet from IP:Self, Ethernet:Self, destined to
	IP:remote-system LinkLayer:remote-system, without transmitting a
	single ARP.</t>

	<t>And of course the simple case, a regular IP unicast that is
	routed via the usual means (so it may be direct to a local system,
	with ARP providing the glue, or it may be to a remote system via
	one or more routers as normal).  In this case, the interfaces are
	always configured.</t>
      </list></t>

	<t>The above isn't as simple as it sounds on a regular BSD socket.
	Many unix implementations will transmit broadcasts not to
	255.255.255.255, but to x.y.z.255 (where x.y.z is the system's local
	subnet).  Such packets are not received by several known DHCP client
	implementations - and it's not their fault, <xref target="RFC2131"/>
	very explicitly demands that these packets' IP destination
	addresses be set to 255.255.255.255.</t>

	<t>Receiving packets sent to 255.255.255.255 isn't a problem on most
	modern unixes...so long as the interface is configured.  When there
	is no IPv4 address on the interface, things become much more murky.</t>

	<t>So, for this convoluted and unfortunate state of affairs in the
	unix systems of the day ISC DHCP was manufactured, in order to do
	what it needs not only to implement the reference but to interoperate
	with other implementations, the software must create some form of
	raw socket to operate on.</t>

	<t>What it actually does is create, for each interface detected on
	the system, a Berkeley Packet Filter socket (or equivalent), and
	program it with a filter that brings in only DHCP packets.  A
	"fallback" UDP Berkeley socket is generally also created, a single
	one no matter how many interfaces.  Should the software need to
	transmit a contrived packet to the local network the packet is
	formed piece by piece and transmitted via the BPF socket.  Hence
	the need to implement many forms of Link Layer framing and above.
	The software gets away with not having to implement IP routing
	tables as well by simply utilizing the aforementioned 'fallback'
	UDP socket when unicasting between two configured systems is
	needed.</t>

	<t>Modern unixes have opened up some facilities that diminish how
	much of this sort of nefarious kludgery is necessary, but have not
	found the state of affairs absolutely resolved.  In particular,
	one might now unicast without ARP by inserting an entry into the
	ARP cache prior to transmitting.  Unconfigured interfaces remain
	the sticking point, however...on virtually no modern unixes is
	it possible to receive broadcast packets unless a local IPv4
	address has been configured, unless it is done with raw sockets.</t>

      <section title="Ethernet Protocol References">
	<t>ISC DHCP Implements Ethernet Version 2 ("DIX"), which is a variant
	of IEEE 802.2.  No good reference of this framing is known to exist
	at this time, but it is vaguely described in <xref target="RFC0894"/>
	see the section titled "Packet format"), and
	the following URL is also thought to be useful.</t>

	<t><eref target="http://en.wikipedia.org/wiki/DIX_Ethernet">http://en.wikipedia.org/wiki/DIX_Ethernet</eref></t>
      </section>

      <section title="Token Ring Protocol References">
	<t>IEEE 802.5 defines the Token Ring framing format used by ISC
	DHCP.</t>
      </section>

      <section title="FDDI Protocol References">
	<t><xref target="RFC1188"/> is the most helpful
	reference ISC DHCP has used to form FDDI packets.</t>
      </section>

      <section title="Internet Protocol Version 4 References">
	<t><xref target="RFC0760">RFC760</xref> fundamentally defines the
	bare IPv4 protocol which ISC DHCP implements.</t>
      </section>

      <section title="Unicast Datagram Protocol References">
	<t><xref target="RFC0768">RFC768</xref> defines the User Datagram
	Protocol that ultimately carries the DHCP or BOOTP protocol.  The
	destination DHCP server port is 67, the client port is 68.  Source
	ports are irrelevant.</t>
      </section>
    </section>

    <section title="BOOTP Protocol References">
	<t>The DHCP Protocol is strange among protocols in that it is
	grafted over the top of another protocol - BOOTP (but we don't
	call it "DHCP over BOOTP" like we do, say "TCP over IP").  BOOTP
	and DHCP share UDP packet formats - DHCP is merely a conventional
	use of both BOOTP header fields and the trailing 'options' space.</t>

	<t>The ISC DHCP server supports BOOTP clients conforming to
	<xref target="RFC0951">RFC951</xref> and <xref target="RFC1542">
	RFC1542</xref>.</t>
    </section>

    <section title="DHCPv4 Protocol References">
      <section title="DHCPv4 Protocol">
	<t>"The DHCP[v4] Protocol" is not defined in a single document.  The
	following collection of references of what ISC DHCP terms "The
	DHCPv4 Protocol".</t>

	<section title="Core Protocol References">
	  <t><xref target="RFC2131">RFC2131</xref> defines the protocol format
	and procedures.  ISC DHCP is not known to diverge from this document
	in any way.  There are, however, a few points on which different
	implementations have arisen out of vagueries in the document.
	DHCP Clients exist which, at one time, present themselves as using
	a Client Identifier Option which is equal to the client's hardware
	address.  Later, the client transmits DHCP packets with no Client
	Identifier Option present - essentially identifying themselves using
	the hardware address.  Some DHCP Servers have been developed which
	identify this client as a single client.  ISC has interpreted
	RFC2131 to indicate that these clients must be treated as two
	separate entities (and hence two, separate addresses).  Client
	behaviour (Embedded Windows products) has developed that relies on
	the former implementation, and hence is incompatible with the
	latter.  Also, RFC2131 demands explicitly that some header fields
	be zeroed upon certain message types.  The ISC DHCP Server instead
	copies many of these fields from the packet received from the client
	or relay, which may not be zero.  It is not known if there is a good
	reason for this that has not been documented.</t>

	  <t><xref target="RFC2132">RFC2132</xref> defines the initial set of
	DHCP Options and provides a great deal of guidance on how to go about
	formatting and processing options.  The document unfortunately
	waffles to a great extent about the NULL termination of DHCP Options,
	and some DHCP Clients (Windows 95) have been implemented that rely
	upon DHCP Options containing text strings to be NULL-terminated (or
	else they crash).  So, ISC DHCP detects if clients null-terminate the
	host-name option and, if so, null terminates any text options it
	transmits to the client.  It also removes NULL termination from any
	known text option it receives prior to any other processing.</t>
	</section>
      </section>

      <section title="DHCPv4 Option References">
	<t><xref target="RFC2241">RFC2241</xref> defines options for
	Novell Directory Services.</t>

	<t><xref target="RFC2242">RFC2242</xref> defines an encapsulated
	option space for NWIP configuration.</t>

	<t><xref target="RFC2485">RFC2485</xref> defines the Open Group's
	UAP option.</t>

	<t><xref target="RFC2610">RFC2610</xref> defines options for
	the Service Location Protocol (SLP).</t>

	<t><xref target="RFC2937">RFC2937</xref> defines the Name Service
	Search Option (not to be confused with the domain-search option).
	The Name Service Search Option allows eg nsswitch.conf to be
	reconfigured via dhcp.  The ISC DHCP server implements this option,
	and the ISC DHCP client is compatible...but does not by default
	install this option's value.  One would need to make their relevant
	dhclient-script process this option in a way that is suitable for
	the system.</t>

	<t><xref target="RFC3004">RFC3004</xref> defines the User-Class
	option.  Note carefully that ISC DHCP currently does not implement
	to this reference, but has (inexplicably) selected an incompatible
	format: a plain text string.</t>

	<t><xref target="RFC3011">RFC3011</xref> defines the Subnet-Selection
	plain DHCPv4 option.  Do not confuse this option with the relay agent
	"link selection" sub-option, although their behaviour is
	similar.</t>

	<t><xref target="RFC3396">RFC3396</xref> documents both how long
	options may be encoded in DHCPv4 packets, and also how multiple
	instances of the same option code within a DHCPv4 packet will be
	decoded by receivers.</t>

	<t><xref target="RFC3397">RFC3397</xref> documents the Domain-Search
	Option, which allows the configuration of the /etc/resolv.conf
	'search' parameter in a way that is <xref target="RFC1035">RFC1035
	</xref> wire format compatible (in fact, it uses the RFC1035 wire
	format).  ISC DHCP has both client and server support, and supports
	RFC1035 name compression.</t>

	<t><xref target="RFC3679">RFC3679</xref> documents a number of
	options that were documented earlier in history, but were not
	made use of.</t>

	<t><xref target="RFC3925">RFC3925</xref> documents a pair of
	Enterprise-ID delimited option spaces for vendors to use in order
	to inform servers of their "vendor class" (sort of like 'uname'
	or 'who and what am I'), and a means to deliver vendor-specific
	and vendor-documented option codes and values.</t>

	<t><xref target="RFC3942">RFC3942</xref> redefined the 'site local'
	option space.</t>

	<t><xref target="RFC4280" /> defines two BCMS server options
	for each protocol family.</t>

	<t><xref target="RFC4388">RFC4388</xref> defined the DHCPv4
	LEASEQUERY message type and a number of suitable response messages,
	for the purpose of sharing information about DHCP served addresses
	and clients.</t>

	<section title="Relay Agent Information Option Options">
	  <t><xref target="RFC3046">RFC3046</xref> defines the Relay Agent
	  Information Option and provides a number of sub-option
	  definitions.</t>

	  <t><xref target="RFC3256">RFC3256</xref> defines the DOCSIS Device
	  Class sub-option.</t>

	  <t><xref target="RFC3527">RFC3527</xref> defines the Link Selection
	  sub-option.</t>
	</section>


	<section title="Dynamic DNS Updates References">
	  <t>The collection of documents that describe the standards-based
	  method to update dns names of DHCP clients starts most easily
	  with <xref target="RFC4703">RFC4703</xref> to define the overall
	  architecture, travels through RFCs <xref target="RFC4702">4702</xref>
	  and <xref target="RFC4704">4704</xref> to describe the DHCPv4 and
	  DHCPv6 FQDN options (to carry the client name), and ends up at
	  <xref target="RFC4701">RFC4701</xref> which describes the DHCID
	  RR used in DNS to perform a kind of atomic locking.</t>

	  <t>ISC DHCP adopted early versions of these documents, and has not
	  yet synchronized with the final standards versions.</t>

	  <t>For RFCs 4702 and 4704, the 'N' bit is not yet supported.  The
	  result is that it is always set zero, and is ignored if set.</t>

	  <t>For RFC4701, which is used to match client identities with names
	  in the DNS as part of name conflict resolution.  Note that ISC DHCP's
	  implementation of DHCIDs vary wildly from this specification.
	  First, ISC DHCP uses a TXT record in which the contents are stored
	  in hexadecimal.  Second, there is a flaw in the selection of the
	  'Identifier Type', which results in a completely different value
	  being selected than was defined in an older revision of this
	  document...also this field is one byte prior to hexadecimal
	  encoding rather than two.  Third, ISC DHCP does not use a digest
	  type code.  Rather, all values for such TXT records are reached
	  via an MD5 sum.  In short, nothing is compatible, but the
	  principle of the TXT record is the same as the standard DHCID
	  record.  However, for DHCPv6 FQDN, we do use DHCID type code '2',
	  as no other value really makes sense in our context.</t>
	</section>

	<section title="Experimental: Failover References">
	  <t>The Failover Protocol defines means by which two DHCP Servers
	  can share all the relevant information about leases granted to
	  DHCP clients on given networks, so that one of the two servers may
	  fail and be survived by a server that can act responsibly.</t>

	  <t>Unfortunately it has been quite some years (2003) since the last
	  time this document was edited, and the authors no longer show any
	  interest in fielding comments or improving the document.</t>

	  <t>The status of this protocol is very unsure, but ISC's
	  implementation of it has proven stable and suitable for use in
	  sizable production environments.</t>

	  <t><xref target="draft-failover">draft-ietf-dhc-failover-12.txt</xref>
	  describes the Failover Protocol.  In addition to what is described
	  in this document, ISC DHCP has elected to make some experimental
	  changes that may be revoked in a future version of ISC DHCP (if the
	  draft authors do not adopt the new behaviour).  Specifically, ISC
	  DHCP's POOLREQ behaviour differs substantially from what is
	  documented in the draft, and the server also implements a form of
	  'MAC Address Affinity' which is not described in the failover
	  document.  The full nature of these changes have been described on
	  the IETF DHC WG mailing list (which has archives), and also in ISC
	  DHCP's manual pages.  Also note that although this document
	  references a RECOVER-WAIT state, it does not document a protocol
	  number assignment for this state.  As a consequence, ISC DHCP has
	  elected to use the value 254.</t>

	  <t> An optimization described in the failover protocol draft
	  is included since 4.2.0a1. It permits a DHCP server
	  operating in communications-interrupted state to 'rewind' a
	  lease to the state most recently transmitted to its peer,
	  greatly increasing a server's endurance in
	  communications-interrupted.  This is supported using a new
	  'rewind state' record on the dhcpd.leases entry for each
	  lease.
	  </t>

	  <t><xref target="RFC3074" /> describes the Load Balancing
	  Algorithm (LBA) that ISC DHCP uses in concert with the Failover
	  protocol.  Note that versions 3.0.* are known to misimplement the
	  hash algorithm (it will only use the low 4 bits of every byte of
	  the hash bucket array).</t>
	</section>
      </section>

      <section title="DHCP Procedures">
	<t><xref target="RFC2939" /> explains how to go about
	obtaining a new DHCP Option code assignment.</t>
      </section>
    </section>


    <section title="DHCPv6 Protocol References">

      <section title="DHCPv6 Protocol References">
	<t>For now there is only one document that specifies the base
	of the DHCPv6 protocol (there have been no updates yet),
	<xref target="RFC3315"/>.</t>

	<t>Support for DHCPv6 was first added in version 4.0.0.  The server
	and client support only IA_NA.  While the server does support multiple
	IA_NAs within one packet from the client, our client only supports
	sending one.  There is no relay support.</t>

	<t>DHCPv6 introduces some new and uncomfortable ideas to the common
	software library.</t>

	<t>
	<list style="numbers">
	  <t>Options sometimes may appear multiple times.  The common
	  library used to treat all appearance of multiple options as
	  specified in RFC2131 - to be concatenated.  DHCPv6 options
	  may sometimes appear multiple times (such as with IA_NA or
	  IAADDR), but often must not. As of 4.2.1-P1, multiple IA_NA, IA_PD
	  or IA_TA are not supported.</t>

	  <t>The same option space appears in DHCPv6 packets multiple times.
	  If the packet was got via a relay, then the client's packet is
	  stored to an option within the relay's packet...if there were two
	  relays, this recurses.  At each of these steps, the root "DHCPv6
	  option space" is used.  Further, a client packet may contain an
	  IA_NA, which may contain an IAADDR - but really, in an abstract
	  sense, this is again re-encapsulation of the DHCPv6 option space
	  beneath options it also contains.</t>
	</list>
	</t>

	<t>Precisely how to correctly support the above conundrums has not
	quite yet been settled, so support is incomplete.</t>

	<t><xref target="RFC5453"/> creates a registry at IANA to reserve
	interface identifiers and specifies a starting set.  These IIDs should
	not be used when constructing addresses to avoid possible conflicts.</t>
      </section>

      <section title="DHCPv6 Options References">
	<t><xref target="RFC3319"/> defines the SIP server
	options for DHCPv6.</t>

	<t><xref target="RFC3646"/> documents the DHCPv6
	name-servers and domain-search options.</t>

	<t><xref target="RFC3633"/> documents the Identity
	Association Prefix Delegation for DHCPv6, which is included
	here for protocol wire reference, but which is not supported
	by ISC DHCP.</t>

	<t><xref target="RFC3898"/> documents four NIS options
	for delivering NIS servers and domain information in DHCPv6.</t>

	<t><xref target="RFC4075"/> defines the DHCPv6 SNTP
	Servers option.</t>

	<t><xref target="RFC4242"/> defines the Information
	Refresh Time option, which advises DHCPv6 Information-Request
	clients to return for updated information.</t>

	<t><xref target="RFC4280"/> defines two BCMS server options
	for each protocol family.</t>

	<t><xref target="RFC4580"/> defines a DHCPv6
	subscriber-id option, which is similar in principle to the DHCPv4
	relay agent option of the same name.</t>

	<t><xref target="RFC4649"/> defines a DHCPv6 remote-id
	option, which is similar in principle to the DHCPv4 relay agent
	remote-id.</t>

      </section>
    </section>

  </middle>

  <back>
    <references title="Published DHCPv4 References">
	&rfc760;
	&rfc768;
	&rfc894;
	&rfc951;
	&rfc1035;
	&rfc1188;
	&rfc1542;
	&rfc2131;
	&rfc2132;
	&rfc2241;
	&rfc2242;
	&rfc2485;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2563'?>
	&rfc2610;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2855'?>
	&rfc2937;
	&rfc2939;
	&rfc3004;
	&rfc3011;
	&rfc3046;
	&rfc3074;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3118'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3203'?>
	&rfc3256;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3361'?>
	&rfc3396;
	&rfc3397;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3442'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3456'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3495'?>
	&rfc3527;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3594'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3634'?>
	&rfc3679;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3825'?>
	&rfc3925;
	&rfc3942;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3993'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4014'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4030'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4039'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4174'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4243'?>
	&rfc4361;
	&rfc4388;
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4390'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4436'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4701'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4702'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4703'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5010'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5071'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5107'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5192'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5223'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5859'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5969'?>

	<reference anchor='draft-failover'>
	  <front>
	    <title>DHCP Failover Protocol</title>
	    <author initials='R.' surname='Droms' fullname='Ralph Droms'>
		<organization abbrev='Cisco'>Cisco Systems</organization>
	    </author>
	    <date month='March' year='2003'/>
	  </front>
	  <format type="TXT" octets="312151" target="https://www.isc.org/sw/dhcp/drafts/draft-ietf-dhc-failover-12.txt"/>
	</reference>

	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-dhcpv4-relay-encapsulation-00.xml'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-dhcpv4-bulk-leasequery-03.xml'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-leasequery-by-remote-id-09.xml'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-relay-id-suboption-07.xml'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-mip6-hiopt-17.xml'?>

    </references>

    <references title="Published Common (DHCPv4/DHCPv6) References">
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4280'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4477'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4578'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4776'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4833'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5417'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5678'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5908'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5970'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5986'?>
	<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-vpn-option-12.xml'?>

    </references>

    <references title="Published DHCPv6 References">

      &rfc3315;
      &rfc3319;
      &rfc3633;
      &rfc3646;
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3736'?>
      &rfc3898;
      &rfc4075;
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4076'?>
      &rfc4242;
      &rfc4580;
      &rfc4649;
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4704'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4994'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5007'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5453'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5460'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-mif-dhcpv6-route-option'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-dhc-dhcpv6-ldra'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-dhc-dhcpv6-relay-supplied-options'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-pd-exclude-01.xml'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-secure-dhcpv6-02.xml'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-mext-nemo-pd'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-dhc-duid-uuid-03.xml'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-softwire-ds-lite-tunnel-option-10.xml'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-mif-dns-server-selection-01.xml'?>
      <?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-geopriv-rfc3825bis-17.xml'?>

      <reference anchor='draft-addr-params'>
	<front>
	  <title>Address Parameters Option for DHCPv6</title>
	  <author initials='T.' surname='Mrugalski' fullname='Mrugalski'>
	    <organization abbrev='Cisco'>Gdansk University of Technology</organization>
	  </author>
	  <date month='April' year='2007'/>
	</front>
	<format type="TXT" target="http://klub.com.pl/dhcpv6/doc/draft-mrugalski-addropts-XX-2007-04-17.txt"/>
      </reference>

    </references>
  </back>
</rfc>