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
|
<pre>Network Working Group P. Traina
Request for Comments: 5065 Blissfully Retired
Obsoletes: <a href="./rfc3065">3065</a> D. McPherson
Category: Standards Track Arbor Networks
J. Scudder
Juniper Networks
August 2007
<span class="h1">Autonomous System Confederations for BGP</span>
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The Border Gateway Protocol (BGP) is an inter-autonomous system
routing protocol designed for Transmission Control Protocol/Internet
Protocol (TCP/IP) networks. BGP requires that all BGP speakers
within a single autonomous system (AS) must be fully meshed. This
represents a serious scaling problem that has been well documented in
a number of proposals.
This document describes an extension to BGP that may be used to
create a confederation of autonomous systems that is represented as a
single autonomous system to BGP peers external to the confederation,
thereby removing the "full mesh" requirement. The intention of this
extension is to aid in policy administration and reduce the
management complexity of maintaining a large autonomous system.
This document obsoletes <a href="./rfc3065">RFC 3065</a>.
<span class="grey">Traina, et al. Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
<a href="#section-1.1">1.1</a>. Specification of Requirements ..............................<a href="#page-3">3</a>
<a href="#section-1.2">1.2</a>. Terminology ................................................<a href="#page-3">3</a>
<a href="#section-2">2</a>. Discussion ......................................................<a href="#page-4">4</a>
<a href="#section-3">3</a>. AS_CONFED Segment Type Extension ................................<a href="#page-5">5</a>
<a href="#section-4">4</a>. Operation .......................................................<a href="#page-5">5</a>
<a href="#section-4.1">4.1</a>. AS_PATH Modification Rules .................................<a href="#page-6">6</a>
<a href="#section-5">5</a>. Error Handling ..................................................<a href="#page-8">8</a>
<a href="#section-5.1">5.1</a>. Error Handling .............................................<a href="#page-8">8</a>
<a href="#section-5.2">5.2</a>. MED and LOCAL_PREF Handling ................................<a href="#page-8">8</a>
<a href="#section-5.3">5.3</a>. AS_PATH and Path Selection .................................<a href="#page-9">9</a>
<a href="#section-6">6</a>. Compatibility Considerations ...................................<a href="#page-10">10</a>
<a href="#section-7">7</a>. Deployment Considerations ......................................<a href="#page-10">10</a>
<a href="#section-8">8</a>. Security Considerations ........................................<a href="#page-10">10</a>
<a href="#section-9">9</a>. Acknowledgments ................................................<a href="#page-11">11</a>
<a href="#section-10">10</a>. References ....................................................<a href="#page-11">11</a>
<a href="#section-10.1">10.1</a>. Normative References .....................................<a href="#page-11">11</a>
<a href="#section-10.2">10.2</a>. Informative References ...................................<a href="#page-11">11</a>
<a href="#appendix-A">Appendix A</a>. Aggregate Routing Information .........................<a href="#page-13">13</a>
<a href="#appendix-B">Appendix B</a>. Changes from <a href="./rfc3065">RFC 3065</a> .................................<a href="#page-13">13</a>
<span class="grey">Traina, et al. Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
As originally defined, BGP requires that all BGP speakers within a
single AS must be fully meshed. The result is that for n BGP
speakers within an AS, n*(n-1)/2 unique Internal BGP (IBGP) sessions
are required. This "full mesh" requirement clearly does not scale
when there are a large number of IBGP speakers within the autonomous
system, as is common in many networks today.
This scaling problem has been well documented and a number of
proposals have been made to alleviate this, such as [<a href="./rfc2796">RFC2796</a>] and
[<a href="./rfc1863" title=""A BGP/IDRP Route Server alternative to a full mesh routing"">RFC1863</a>] (made historic by [<a href="./rfc4223" title=""Reclassification of RFC 1863 to Historic"">RFC4223</a>]). This document presents
another alternative alleviating the need for a "full mesh" and is
known as "Autonomous System Confederations for BGP", or simply, "BGP
confederations". It has also been observed that BGP confederations
may provide improvements in routing policy control.
This document is a revision of, and obsoletes, [<a href="./rfc3065" title=""Autonomous System Confederations for BGP"">RFC3065</a>], which is
itself a revision of [<a href="./rfc1965" title=""Autonomous System Confederations for BGP"">RFC1965</a>]. It includes editorial changes,
terminology clarifications, and more explicit protocol specifications
based on extensive implementation and deployment experience with BGP
Confederations.
<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>. Specification of Requirements</span>
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 <a href="./rfc2119">RFC 2119</a> [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>. Terminology</span>
AS Confederation
A collection of autonomous systems represented and advertised as a
single AS number to BGP speakers that are not members of the local
BGP confederation.
AS Confederation Identifier
An externally visible autonomous system number that identifies a
BGP confederation as a whole.
Member Autonomous System (Member-AS)
An autonomous system that is contained in a given AS
confederation. Note that "Member Autonomous System" and "Member-
AS" are used entirely interchangeably throughout this document.
<span class="grey">Traina, et al. Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
Member-AS Number
An autonomous system number identifier visible only within a BGP
confederation, and used to represent a Member-AS within that
confederation.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Discussion</span>
It may be useful to subdivide autonomous systems with a very large
number of BGP speakers into smaller domains for purposes of
controlling routing policy via information contained in the BGP
AS_PATH attribute. For example, one may choose to consider all BGP
speakers in a geographic region as a single entity.
In addition to potential improvements in routing policy control, if
techniques such as those presented here or in [<a href="./rfc4456" title=""BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)"">RFC4456</a>] are not
employed, [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>] requires BGP speakers in the same autonomous system
to establish a full mesh of TCP connections among all speakers for
the purpose of exchanging exterior routing information. In
autonomous systems, the number of intra-domain connections that need
to be maintained by each border router can become significant.
Subdividing a large autonomous system allows a significant reduction
in the total number of intra-domain BGP connections, as the
connectivity requirements simplify to the model used for inter-domain
connections.
Unfortunately, subdividing an autonomous system may increase the
complexity of routing policy based on AS_PATH information for all
members of the Internet. Additionally, this division increases the
maintenance overhead of coordinating external peering when the
internal topology of this collection of autonomous systems is
modified.
Therefore, division of an autonomous system into separate systems may
adversely affect optimal routing of packets through the Internet.
However, there is usually no need to expose the internal topology of
this divided autonomous system, which means it is possible to regard
a collection of autonomous systems under a common administration as a
single entity or autonomous system, when viewed from outside the
confines of the confederation of autonomous systems itself.
<span class="grey">Traina, et al. Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. AS_CONFED Segment Type Extension</span>
Currently, BGP specifies that the AS_PATH attribute is a well-known
mandatory attribute that is composed of a sequence of AS path
segments. Each AS path segment is represented by a triple <path
segment type, path segment length, path segment value>.
In [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>], the path segment type is a 1-octet field with the two
following values defined:
Value Segment Type
1 AS_SET: unordered set of autonomous systems that a route in
the UPDATE message has traversed
2 AS_SEQUENCE: ordered set of autonomous systems that a route
in the UPDATE message has traversed
This document specifies two additional segment types:
3 AS_CONFED_SEQUENCE: ordered set of Member Autonomous
Systems in the local confederation that the UPDATE message
has traversed
4 AS_CONFED_SET: unordered set of Member Autonomous Systems
in the local confederation that the UPDATE message has
traversed
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Operation</span>
A member of a BGP confederation MUST use its AS Confederation
Identifier in all transactions with peers that are not members of its
confederation. This AS Confederation Identifier is the "externally
visible" AS number, and this number is used in OPEN messages and
advertised in the AS_PATH attribute.
A member of a BGP confederation MUST use its Member-AS Number in all
transactions with peers that are members of the same confederation as
the local BGP speaker.
A BGP speaker receiving an AS_PATH attribute containing an autonomous
system matching its own AS Confederation Identifier SHALL treat the
path in the same fashion as if it had received a path containing its
own AS number.
<span class="grey">Traina, et al. Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
A BGP speaker receiving an AS_PATH attribute containing an
AS_CONFED_SEQUENCE or AS_CONFED_SET that contains its own Member-AS
Number SHALL treat the path in the same fashion as if it had received
a path containing its own AS number.
<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. AS_PATH Modification Rules</span>
When implementing BGP confederations, Section 5.1.2 of [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>] is
replaced with the following text:
AS_PATH is a well-known mandatory attribute. This attribute
identifies the autonomous systems through which routing information
carried in this UPDATE message has passed. The components of this
list can be AS_SETs, AS_SEQUENCEs, AS_CONFED_SETs or
AS_CONFED_SEQUENCES.
When a BGP speaker propagates a route it learned from another BGP
speaker's UPDATE message, it modifies the route's AS_PATH attribute
based on the location of the BGP speaker to which the route will be
sent:
a) When a given BGP speaker advertises the route to another BGP
speaker located in its own Member-AS, the advertising speaker
SHALL NOT modify the AS_PATH attribute associated with the route.
b) When a given BGP speaker advertises the route to a BGP speaker
located in a neighboring autonomous system that is a member of the
local confederation, the advertising speaker updates the AS_PATH
attribute as follows:
1) if the first path segment of the AS_PATH is of type
AS_CONFED_SEQUENCE, the local system prepends its own Member-AS
number as the last element of the sequence (put it in the
leftmost position with respect to the position of octets in the
protocol message). If the act of prepending will cause an
overflow in the AS_PATH segment (i.e., more than 255 ASs), it
SHOULD prepend a new segment of type AS_CONFED_SEQUENCE and
prepend its own AS number to this new segment.
2) if the first path segment of the AS_PATH is not of type
AS_CONFED_SEQUENCE, the local system prepends a new path
segment of type AS_CONFED_SEQUENCE to the AS_PATH, including
its own Member-AS Number in that segment.
3) if the AS_PATH is empty, the local system creates a path
segment of type AS_CONFED_SEQUENCE, places its own Member-AS
Number into that segment, and places that segment into the
AS_PATH.
<span class="grey">Traina, et al. Standards Track [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
c) When a given BGP speaker advertises the route to a BGP speaker
located in a neighboring autonomous system that is not a member of
the local confederation, the advertising speaker SHALL update the
AS_PATH attribute as follows:
1) if any path segments of the AS_PATH are of the type
AS_CONFED_SEQUENCE or AS_CONFED_SET, those segments MUST be
removed from the AS_PATH attribute, leaving the sanitized
AS_PATH attribute to be operated on by steps 2, 3 or 4.
2) if the first path segment of the remaining AS_PATH is of type
AS_SEQUENCE, the local system prepends its own AS Confederation
Identifier as the last element of the sequence (put it in the
leftmost position with respect to the position of octets in the
protocol message). If the act of prepending will cause an
overflow in the AS_PATH segment (i.e., more than 255 ASs), it
SHOULD prepend a new segment of type AS_SEQUENCE and prepend
its own AS number to this new segment.
3) if the first path segment of the remaining AS_PATH is of type
AS_SET, the local system prepends a new path segment of type
AS_SEQUENCE to the AS_PATH, including its own AS Confederation
Identifier in that segment.
4) if the remaining AS_PATH is empty, the local system creates a
path segment of type AS_SEQUENCE, places its own AS
Confederation Identifier into that segment, and places that
segment into the AS_PATH.
When a BGP speaker originates a route then:
a) the originating speaker includes its own AS Confederation
Identifier in a path segment, of type AS_SEQUENCE, in the AS_PATH
attribute of all UPDATE messages sent to BGP speakers located in
neighboring autonomous systems that are not members of the local
confederation. In this case, the AS Confederation Identifier of
the originating speaker's autonomous system will be the only entry
the path segment, and this path segment will be the only segment
in the AS_PATH attribute.
b) the originating speaker includes its own Member-AS Number in a
path segment, of type AS_CONFED_SEQUENCE, in the AS_PATH attribute
of all UPDATE messages sent to BGP speakers located in neighboring
Member Autonomous Systems that are members of the local
confederation. In this case, the Member-AS Number of the
originating speaker's autonomous system will be the only entry the
path segment, and this path segment will be the only segment in
the AS_PATH attribute.
<span class="grey">Traina, et al. Standards Track [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
c) the originating speaker includes an empty AS_PATH attribute in all
UPDATE messages sent to BGP speakers residing within the same
Member-AS. (An empty AS_PATH attribute is one whose length field
contains the value zero).
Whenever the modification of the AS_PATH attribute calls for
including or prepending the AS Confederation Identifier or Member-AS
Number of the local system, the local system MAY include/prepend more
than one instance of that value in the AS_PATH attribute. This is
controlled via local configuration.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Error Handling</span>
A BGP speaker MUST NOT transmit updates containing AS_CONFED_SET or
AS_CONFED_SEQUENCE attributes to peers that are not members of the
local confederation.
It is an error for a BGP speaker to receive an UPDATE message with an
AS_PATH attribute that contains AS_CONFED_SEQUENCE or AS_CONFED_SET
segments from a neighbor that is not located in the same
confederation. If a BGP speaker receives such an UPDATE message, it
SHALL treat the message as having a malformed AS_PATH according to
the procedures of [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>], Section 6.3 ("UPDATE Message Error
Handling").
It is a error for a BGP speaker to receive an update message from a
confederation peer that is not in the same Member-AS that does not
have AS_CONFED_SEQUENCE as the first segment. If a BGP speaker
receives such an UPDATE message, it SHALL treat the message as having
a malformed AS_PATH according to the procedures of [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>], <a href="#section-6.3">Section</a>
<a href="#section-6.3">6.3</a> ("UPDATE Message Error Handling").
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. Common Administrative Issues</span>
It is reasonable for Member Autonomous Systems of a confederation to
share a common administration and Interior Gateway Protocol (IGP)
information for the entire confederation. It is also reasonable for
each Member-AS to run an independent IGP. In the latter case, the
NEXT_HOP may need to be set using policy (i.e., by default it is
unchanged).
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. MED and LOCAL_PREF Handling</span>
It SHALL be legal for a BGP speaker to advertise an unchanged
NEXT_HOP and MULTI_EXIT_DISC (MED) attribute to peers in a
neighboring Member-AS of the local confederation.
<span class="grey">Traina, et al. Standards Track [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
MEDs of two routes SHOULD only be compared if the first autonomous
systems in the first AS_SEQUENCE in both routes are the same -- i.e.,
skip all the autonomous systems in the AS_CONFED_SET and
AS_CONFED_SEQUENCE. An implementation MAY provide the ability to
configure path selection such that MEDs of two routes are comparable
if the first autonomous systems in the AS_PATHs are the same,
regardless of AS_SEQUENCE or AS_CONFED_SEQUENCE in the AS_PATH.
An implementation MAY compare MEDs received from a Member-AS via
multiple paths. An implementation MAY compare MEDs from different
Member Autonomous Systems of the same confederation.
In addition, the restriction against sending the LOCAL_PREF attribute
to peers in a neighboring autonomous system within the same
confederation is removed.
<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>. AS_PATH and Path Selection</span>
Path selection criteria for information received from members inside
a confederation MUST follow the same rules used for information
received from members inside the same autonomous system, as specified
in [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>].
In addition, the following rules SHALL be applied:
1) If the AS_PATH is internal to the local confederation (i.e., there
are only AS_CONFED_* segments), consider the neighbor AS to be the
local AS.
2) Otherwise, if the first segment in the path that is not an
AS_CONFED_SEQUENCE or AS_CONFED_SET is an AS_SEQUENCE, consider
the neighbor AS to be the leftmost AS_SEQUENCE AS.
3) When comparing routes using AS_PATH length, CONFED_SEQUENCE and
CONFED_SETs SHOULD NOT be counted.
4) When comparing routes using the internal (IBGP learned) versus
external (EBGP learned) rules, treat a route that is learned from
a peer that is in the same confederation (not necessarily the same
Member-AS) as "internal".
<span class="grey">Traina, et al. Standards Track [Page 9]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. Compatibility Considerations</span>
All BGP speakers participating as members of a confederation MUST
recognize the AS_CONFED_SET and AS_CONFED_SEQUENCE segment type
extensions to the AS_PATH attribute.
Any BGP speaker not supporting these extensions will generate a
NOTIFICATION message specifying an "UPDATE Message Error" and a sub-
code of "Malformed AS_PATH".
This compatibility issue implies that all BGP speakers participating
in a confederation MUST support BGP confederations. However, BGP
speakers outside the confederation need not support these extensions.
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Deployment Considerations</span>
BGP confederations have been widely deployed throughout the Internet
for a number of years and are supported by multiple vendors.
Improper configuration of BGP confederations can cause routing
information within an AS to be duplicated unnecessarily. This
duplication of information will waste system resources, cause
unnecessary route flaps, and delay convergence.
Care should be taken to manually filter duplicate advertisements
caused by reachability information being relayed through multiple
Member Autonomous Systems based upon the topology and redundancy
requirements of the confederation.
Additionally, confederations (as well as route reflectors), by
excluding different reachability information from consideration at
different locations in a confederation, have been shown [<a href="./rfc3345" title=""Border Gateway Protocol (BGP) Persistent Route Oscillation Condition"">RFC3345</a>] to
cause permanent oscillation between candidate routes when using the
tie-breaking rules required by BGP [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>]. Care must be taken when
selecting MED values and tie-breaking policy to avoid these
situations.
One potential way to avoid this is by configuring inter-Member-AS IGP
metrics higher than intra-Member-AS IGP metrics and/or using other
tie-breaking policies to avoid BGP route selection based on
incomparable MEDs.
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Security Considerations</span>
This extension to BGP does not change the underlying security issues
inherent in the existing BGP protocol, such as those described in
[<a href="./rfc2385" title=""Protection of BGP Sessions via the TCP MD5 Signature Option"">RFC2385</a>] and [BGP-VULN].
<span class="grey">Traina, et al. Standards Track [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Acknowledgments</span>
The general concept of BGP confederations was taken from IDRP's
Routing Domain Confederations [<a href="#ref-ISO10747" title=""Inter-Domain Routing Protocol"">ISO10747</a>]. Some of the introductory
text in this document was taken from [<a href="./rfc2796">RFC2796</a>].
The authors would like to acknowledge Jeffrey Haas for his extensive
feedback on this document. We'd also like to thank Bruce Cole,
Srihari Ramachandra, Alex Zinin, Naresh Kumar Paliwal, Jeffrey Haas,
Cengiz Alaettinoglu, Mike Hollyman, and Bruno Rijsman for their
feedback and suggestions.
Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for
providing constructive and valuable feedback on earlier versions of
this specification.
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. References</span>
<span class="h3"><a class="selflink" id="section-10.1" href="#section-10.1">10.1</a>. Normative References</span>
[<a id="ref-BGP-4">BGP-4</a>] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", <a href="./rfc4271">RFC 4271</a>, January
2006.
[<a id="ref-RFC1965">RFC1965</a>] Traina, P., "Autonomous System Confederations for BGP",
<a href="./rfc1965">RFC 1965</a>, June 1996.
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC3065">RFC3065</a>] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", <a href="./rfc3065">RFC 3065</a>, February 2001.
<span class="h3"><a class="selflink" id="section-10.2" href="#section-10.2">10.2</a>. Informative References</span>
[<a id="ref-ISO10747">ISO10747</a>] Kunzinger, C., Editor, "Inter-Domain Routing Protocol",
ISO/IEC 10747, October 1993.
[<a id="ref-RFC1863">RFC1863</a>] Haskin, D., "A BGP/IDRP Route Server alternative to a full
mesh routing", <a href="./rfc1863">RFC 1863</a>, October 1995.
[<a id="ref-RFC2385">RFC2385</a>] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", <a href="./rfc2385">RFC 2385</a>, August 1998.
[<a id="ref-RFC3345">RFC3345</a>] McPherson, D., Gill, V., Walton, D., and A. Retana,
"Border Gateway Protocol (BGP) Persistent Route
Oscillation Condition", <a href="./rfc3345">RFC 3345</a>, August 2002.
<span class="grey">Traina, et al. Standards Track [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
[<a id="ref-RFC4223">RFC4223</a>] Savola, P., "Reclassification of <a href="./rfc1863">RFC 1863</a> to Historic",
<a href="./rfc4223">RFC 4223</a>, October 2005.
[<a id="ref-RFC4272">RFC4272</a>] Murphy, S., "BGP Security Vulnerabilities Analysis", <a href="./rfc4272">RFC</a>
<a href="./rfc4272">4272</a>, January 2006.
[<a id="ref-RFC4456">RFC4456</a>] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", <a href="./rfc4456">RFC 4456</a>, April 2006.
<span class="grey">Traina, et al. Standards Track [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Aggregate Routing Information</span>
As a practical matter, aggregation as discussed in [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>], <a href="#section-9.2.2.2">Section</a>
<a href="#section-9.2.2.2">9.2.2.2</a>, is not generally employed within confederations. However,
in the event that such aggregation is performed within a
confederation, the rules of [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>] should be followed, making the
necessary substitutions between AS_SET and AS_CONFED_SET and
similarly, AS_SEQUENCE and AS_CONFED_SEQUENCE. Confederation-type
segments (AS_CONFED_SET and AS_CONFED_SEQUENCE) MUST be kept separate
from non-confederation segments (AS_SET and AS_SEQUENCE). An
implementation could also choose to provide a form of aggregation
wherein non-confederation segments are aggregated as discussed in
[<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>], Section 9.2.2.2, and confederation-type segments are not
aggregated.
Support for aggregation of confederation-type segments is not
mandatory.
<span class="h2"><a class="selflink" id="appendix-B" href="#appendix-B">Appendix B</a>. Changes from <a href="./rfc3065">RFC 3065</a></span>
The primary trigger for an update to <a href="./rfc3065">RFC 3065</a> was regarding issues
associated with AS path segment handling, in particular what to do
when interacting with BGP peers external to a confederation and to
ensure AS_CONFED_[SET|SEQUENCE] segment types are not propagated to
peers outside of a confederation.
As such, the "Error Handling" section above was added and applies not
only to BGP confederation speakers, but to all BGP speakers.
Other changes are mostly trivial and surrounding some clarification
and consistency in terminology and denoting that
AS_CONFED_[SET|SEQUENCE] Segment Type handling should be just as it
is in the base BGP specification [<a href="#ref-BGP-4" title=""A Border Gateway Protocol 4 (BGP-4)"">BGP-4</a>].
Authors' Addresses
Paul Traina
Blissfully Retired
Email: bgp-confederations@st04.pst.org
Danny McPherson
Arbor Networks
EMail: danny@arbor.net
John G. Scudder
Juniper Networks
EMail: jgs@juniper.net
<span class="grey">Traina, et al. Standards Track [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc5065">RFC 5065</a> August 2007</span>
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
retain all their rights.
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, THE IETF TRUST 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.
Intellectual Property
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 <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and <a href="https://www.rfc-editor.org/bcp/bcp79">BCP 79</a>.
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
<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Traina, et al. Standards Track [Page 14]
</pre>
|
