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
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
|
Network Working Group R. Austein
Internet-Draft ISC
Expires: July 15, 2006 January 11, 2006
DNS Name Server Identifier Option (NSID)
draft-ietf-dnsext-nsid-01
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 15, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
With the increased use of DNS anycast, load balancing, and other
mechanisms allowing more than one DNS name server to share a single
IP address, it is sometimes difficult to tell which of a pool of name
servers has answered a particular query. While existing ad-hoc
mechanism allow an operator to send follow-up queries when it is
necessary to debug such a configuration, the only completely reliable
way to obtain the identity of the name server which responded is to
have the name server include this information in the response itself.
This note defines a protocol extension to support this functionality.
Austein Expires July 15, 2006 [Page 1]
Internet-Draft DNS NSID January 2006
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Resolver Behavior . . . . . . . . . . . . . . . . . . . . 4
2.2. Name Server Behavior . . . . . . . . . . . . . . . . . . . 4
2.3. The NSID Option . . . . . . . . . . . . . . . . . . . . . 4
2.4. Presentation Format . . . . . . . . . . . . . . . . . . . 5
3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. The NSID Payload . . . . . . . . . . . . . . . . . . . . . 6
3.2. NSID Is Not Transitive . . . . . . . . . . . . . . . . . . 8
3.3. User Interface Issues . . . . . . . . . . . . . . . . . . 8
3.4. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
Austein Expires July 15, 2006 [Page 2]
Internet-Draft DNS NSID January 2006
1. Introduction
With the increased use of DNS anycast, load balancing, and other
mechanisms allowing more than one DNS name server to share a single
IP address, it is sometimes difficult to tell which of a pool of name
servers has answered a particular query.
Existing ad-hoc mechanisms allow an operator to send follow-up
queries when it is necessary to debug such a configuration, but there
are situations in which this is not a totally satisfactory solution,
since anycast routing may have changed, or the server pool in
question may be behind some kind of extremely dynamic load balancing
hardware. Thus, while these ad-hoc mechanisms are certainly better
than nothing (and have the advantage of already being deployed), a
better solution seems desirable.
Given that a DNS query is an idempotent operation with no retained
state, it would appear that the only completely reliable way to
obtain the identity of the name server which responded to a
particular query is to have that name server include identifying
information in the response itself. This note defines a protocol
enhancement to achieve this.
1.1. Reserved Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Austein Expires July 15, 2006 [Page 3]
Internet-Draft DNS NSID January 2006
2. Protocol
This note uses an EDNS [RFC2671] option to signal the resolver's
desire for information identifying the name server and to hold the
name server's response, if any.
2.1. Resolver Behavior
A resolver signals its desire for information identifying a name
server by sending an empty NSID option (Section 2.3) in an EDNS OPT
pseudo-RR in the query message.
The resolver MUST NOT include any NSID payload data in the query
message.
The semantics of an NSID request are not transitive. That is: the
presence of an NSID option in a query is a request that the name
server which receives the query identify itself. If the name server
side of a recursive name server receives an NSID request, the client
is asking the recursive name server to identify itself; if the
resolver side of the recursive name server wishes to receive
identifying information, it is free to add NSID requests in its own
queries, but that is a separate matter.
2.2. Name Server Behavior
A name server which understands the NSID option and chooses to honor
a particular NSID request responds by including identifying
information in a NSID option (Section 2.3) in an EDNS OPT pseudo-RR
in the response message.
The name server MUST ignore any NSID payload data that might be
present in the query message.
The NSID option is not transitive. A name server MUST NOT send an
NSID option back to a resolver which did not request it. In
particular, while a recursive name server may choose to add an NSID
option when sending a query, this has no effect on the presence or
absence of the NSID option in the recursive name server's response to
the original client.
As stated in Section 2.1, this mechanism is not restricted to
authoritative name servers; the semantics are intended to be equally
applicable to recursive name servers.
2.3. The NSID Option
The OPTION-CODE for the NSID option is [TBD].
Austein Expires July 15, 2006 [Page 4]
Internet-Draft DNS NSID January 2006
The OPTION-DATA for the NSID option is an opaque byte string the
semantics of which are deliberately left outside the protocol. See
Section 3.1 for discussion.
2.4. Presentation Format
User interfaces MUST read and write the content of the NSID option as
a sequence of hexadecimal digits, two digits per payload octet.
The NSID payload is binary data. Any comparison between NSID
payloads MUST be a comparison of the raw binary data. Copy
operations MUST NOT assume that the raw NSID payload is null-
terminated. Any resemblance between raw NSID payload data and any
form of text is purely a convenience, and does not change the
underlying nature of the payload data.
See Section 3.3 for discussion.
Austein Expires July 15, 2006 [Page 5]
Internet-Draft DNS NSID January 2006
3. Discussion
This section discusses certain aspects of the protocol and explains
considerations that led to the chosen design.
3.1. The NSID Payload
The syntax and semantics of the content of the NSID option is
deliberately left outside the scope of this specification. This
section describe some of the kinds of data that server administrators
might choose to provide as the content of the NSID option, and
explains the reasoning behind choosing a simple opaque byte string.
There are several possibilities for the payload of the NSID option:
o It could be the "real" name of the specific name server within the
name server pool.
o It could be the "real" IP address (IPv4 or IPv6) of the name
server within the name server pool.
o It could be some sort of pseudo-random number generated in a
predictable fashion somehow using the server's IP address or name
as a seed value.
o It could be some sort of probabilisticly unique identifier
initially derived from some sort of random number generator then
preserved across reboots of the name server.
o It could be some sort of dynamicly generated identifier so that
only the name server operator could tell whether or not any two
queries had been answered by the same server.
o It could be a blob of signed data, with a corresponding key which
might (or might not) be available via DNS lookups.
o It could be a blob of encrypted data, the key for which could be
restricted to parties with a need to know (in the opinion of the
server operator).
o It could be an arbitrary string of octets chosen at the discretion
of the name server operator.
Each of these options has advantages and disadvantages:
o Using the "real" name is simple, but the name server may not have
a "real" name.
Austein Expires July 15, 2006 [Page 6]
Internet-Draft DNS NSID January 2006
o Using the "real" address is also simple, and the name server
almost certainly does have at least one non-anycast IP address for
maintenance operations, but the operator of the name server may
not be willing to divulge its non-anycast address.
o Given that one common reason for using anycast DNS techniques is
an attempt to harden a critical name server against denial of
service attacks, some name server operators are likely to want an
identifier other than the "real" name or "real" address of the
name server instance.
o Using a hash or pseudo-random number can provide a fixed length
value that the resolver can use to tell two name servers apart
without necessarily being able to tell where either one of them
"really" is, but makes debugging more difficult if one happens to
be in a friendly open environment. Furthermore, hashing might not
add much value, since a hash based on an IPv4 address still only
involves a 32-bit search space, and DNS names used for servers
that operators might have to debug at 4am tend not to be very
random.
o Probabilisticly unique identifiers have similar properties to
hashed identifiers, but (given a sufficiently good random number
generator) are immune to the search space issues. However, the
strength of this approach is also its weakness: there is no
algorithmic transformation by which even the server operator can
associate name server instances with identifiers while debugging,
which might be annoying. This approach also requires the name
server instance to preserve the probabilisticly unique identifier
across reboots, but this does not appear to be a serious
restriction, since authoritative nameservers almost always have
some form of nonvolatile storage in any case, and in the rare case
of a name server that does not have any way to store such an
identifier, nothing terrible will happen if the name server just
generates a new identifier every time it reboots.
o Using an arbitrary octet string gives name server operators yet
another thing to configure, or mis-configure, or forget to
configure. Having all the nodes in an anycast name server
constellation identify themselves as "My Name Server" would not be
particularly useful.
Given all of the issues listed above, there does not appear to be a
single solution that will meet all needs. Section 2.3 therefore
defines the NSID payload to be an opaque byte string and leaves the
choice up to the implementor and name server operator. The following
guidelines may be useful to implementors and server operators:
Austein Expires July 15, 2006 [Page 7]
Internet-Draft DNS NSID January 2006
o Operators for whom divulging the unicast address is an issue could
use the raw binary representation of a probabilisticly unique
random number. This should probably be the default implementation
behavior.
o Operators for whom divulging the unicast address is not an issue
could just use the raw binary representation of a unicast address
for simplicity. This should only be done via an explicit
configuration choice by the operator.
o Operators who really need or want the ability to set the NSID
payload to an arbitrary value could do so, but this should only be
done via an explicit configuration choice by the operator.
This approach appears to provide enough information for useful
debugging without unintentionally leaking the maintenance addresses
of anycast name servers to nogoodniks, while also allowing name
server operators who do not find such leakage threatening to provide
more information at their own discretion.
3.2. NSID Is Not Transitive
As specified in Section 2.1 and Section 2.2, the NSID option is not
transitive. This is strictly a hop-by-hop mechanism.
Most of the discussion of name server identification to date has
focused on identifying authoritative name servers, since the best
known cases of anycast name servers are a subset of the name servers
for the root zone. However, given that anycast DNS techniques are
also applicable to recursive name servers, the mechanism may also be
useful with recursive name servers. The hop-by-hop semantics support
this.
While there might be some utility in having a transitive variant of
this mechanism (so that, for example, a stub resolver could ask a
recursive server to tell it which authoritative name server provided
a particular answer to the recursive name server), the semantics of
such a variant would be more complicated, and are left for future
work.
3.3. User Interface Issues
Given the range of possible payload contents described in
Section 3.1, it is not possible to define a single presentation
format for the NSID payload that is efficient, convenient,
unambiguous, and aesthetically pleasing. In particular, while it is
tempting to use a presentation format that uses some form of textual
strings, attempting to support this would significantly complicate
Austein Expires July 15, 2006 [Page 8]
Internet-Draft DNS NSID January 2006
what's intended to be a very simple debugging mechanism.
In some cases the content of the NSID payload may be binary data
meaningful only to the name server operator, and may not be
meaningful to the user or application, but the user or application
must be able to capture the entire content anyway in order for it to
be useful. Thus, the presentation format must support arbitrary
binary data.
In cases where the name server operator derives the NSID payload from
textual data, a textual form such as US-ASCII or UTF-8 strings might
at first glance seem easier for a user to deal with. There are,
however, a number of complex issues involving internationalized text
which, if fully addressed here, would require a set of rules
significantly longer than the rest of this specification. See
[RFC2277] for an overview of some of these issues.
It is much more important for the NSID payload data to be passed
unambiguously from server administrator to user and back again than
it is for the payload data data to be pretty while in transit. In
particular, it's critical that it be straightforward for a user to
cut and paste an exact copy of the NSID payload output by a debugging
tool into other formats such as email messages or web forms without
distortion. Hexadecimal strings, while ugly, are also robust.
3.4. Truncation
In some cases, adding the NSID option to a response message may
trigger message truncation. This specification does not change the
rules for DNS message truncation in any way, but implementors will
need to pay attention to this issue.
Including the NSID option in a response is always optional, so this
specification never requires name servers to truncate response
messages.
By definition, a resolver that requests NSID responses also supports
EDNS, so a resolver that requests NSID responses can also use the
"sender's UDP payload size" field of the OPT pseudo-RR to signal a
receive buffer size large enough to make truncation unlikely.
Austein Expires July 15, 2006 [Page 9]
Internet-Draft DNS NSID January 2006
4. IANA Considerations
This mechanism requires allocation of one ENDS option code for the
NSID option (Section 2.3).
Austein Expires July 15, 2006 [Page 10]
Internet-Draft DNS NSID January 2006
5. Security Considerations
This document describes a channel signaling mechanism, intended
primarily for debugging. Channel signaling mechanisms are outside
the scope of DNSSEC per se. Applications that require integrity
protection for the data being signaled will need to use a channel
security mechanism such as TSIG [RFC2845].
Section 3.1 discusses a number of different kinds of information that
a name server operator might choose to provide as the value of the
NSID option. Some of these kinds of information are security
sensitive in some environments. This specification deliberately
leaves the syntax and semantics of the NSID option content up to the
implementation and the name server operator.
Austein Expires July 15, 2006 [Page 11]
Internet-Draft DNS NSID January 2006
6. Acknowledgements
Joe Abley, Harald Alvestrand, Mark Andrews, Roy Arends, Steve
Bellovin, Randy Bush, David Conrad, Johan Ihren, Daniel Karrenberg,
Peter Koch, Mike Patton, Mike StJohns, Paul Vixie, Sam Weiler, and
Suzanne Woolf. Apologies to anyone inadvertently omitted from the
above list.
Austein Expires July 15, 2006 [Page 12]
Internet-Draft DNS NSID January 2006
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, May 2000.
7.2. Informative References
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", RFC 2277, BCP 18, January 1998.
Austein Expires July 15, 2006 [Page 13]
Internet-Draft DNS NSID January 2006
Author's Address
Rob Austein
ISC
950 Charter Street
Redwood City, CA 94063
USA
Email: sra@isc.org
Austein Expires July 15, 2006 [Page 14]
Internet-Draft DNS NSID January 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Austein Expires July 15, 2006 [Page 15]
|