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'BGP-4' ** Obsolete normative reference: RFC 1965 (Obsoleted by RFC 3065) ** Obsolete normative reference: RFC 3065 (Obsoleted by RFC 5065) -- Obsolete informational reference (is this intentional?): RFC 1771 (Obsoleted by RFC 4271) -- Obsolete informational reference (is this intentional?): RFC 1863 (Obsoleted by RFC 4223) -- Obsolete informational reference (is this intentional?): RFC 2385 (Obsoleted by RFC 5925) -- Obsolete informational reference (is this intentional?): RFC 2796 (Obsoleted by RFC 4456) Summary: 8 errors (**), 0 flaws (~~), 6 warnings (==), 12 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT Paul Traina 3 Danny McPherson 4 Arbor Networks, Inc. 5 John Scudder 6 Cisco Systems, Inc. 7 Expires: April 2006 October 2005 9 Autonomous System Confederations for BGP 10 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware have 16 been or will be disclosed, and any of which he or she becomes aware 17 will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that other 21 groups may also distribute working documents as Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other documents 25 at any time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress". 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/1id-abstracts.html 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 Copyright Notice 36 Copyright (C) The Internet Society (2005). All Rights Reserved. 38 Abstract 40 The Border Gateway Protocol (BGP) is an inter-autonomous system 41 routing protocol designed for Transmission Control Protocol/Internet 42 Protocol (TCP/IP) networks. BGP requires that all BGP speakers 43 within a single autonomous system (AS) must be fully meshed. This 44 represents a serious scaling problem that has been well documented in 45 a number of proposals. 47 This document describes an extension to BGP which may be used to 48 create a confederation of autonomous systems that is represented as a 49 single autonomous system to BGP peers external to the confederation, 50 thereby removing the "full mesh" requirement. The intention of this 51 extension is to aid in policy administration and reduce the 52 management complexity of maintaining a large autonomous system. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 5 59 3. AS_CONFED Segment Type Extension . . . . . . . . . . . . . . . 6 60 4. Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 4.1. AS_PATH Modification Rules. . . . . . . . . . . . . . . . . 7 62 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 8 63 5.1. Common Administrative Issues. . . . . . . . . . . . . . . . 9 64 5.2. MED and LOCAL_PREF Handling . . . . . . . . . . . . . . . . 9 65 5.3. AS_PATH and Path Selection. . . . . . . . . . . . . . . . . 10 66 6. Compatability Considerations . . . . . . . . . . . . . . . . . 10 67 7. Deployment Considerations. . . . . . . . . . . . . . . . . . . 11 68 8. Security Considerations. . . . . . . . . . . . . . . . . . . . 11 69 9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 11 70 10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 13 71 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 72 10.2. Informative References . . . . . . . . . . . . . . . . . . 13 73 11. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 14 75 1. Introduction 77 As currently defined, BGP requires that all BGP speakers within a 78 single AS must be fully meshed. The result is that for n BGP 79 speakers within an AS n*(n-1)/2 unique IBGP sessions are required. 80 This "full mesh" requirement clearly does not scale when there are a 81 large number of IBGP speakers within the autonomous system, as is 82 common in many networks today. 84 This scaling problem has been well documented and a number of 85 proposals have been made to alleviate this [RFC 1863, RFC 2796]. 86 This document presents another alternative alleviating the need for a 87 "full mesh" and is known as "Autonomous System Confederations for 88 BGP", or simply, "BGP Confederations". It has also been observed 89 that BGP Confederations may provide improvements in routing policy 90 control. 92 This document is a revision of [RFC 3065], which is itself a revision 93 to [RFC 1965]. It includes editorial changes, terminology 94 clarifications and more explicit protocol specifications based on 95 extensive implementation and deployment experience with BGP 96 Confederations. 98 1.1. Terminology 100 AS Confederation 102 A collection of autonomous systems represented and advertised 103 as a single AS number to BGP speakers that are not members of 104 the local BGP confederation. 106 AS Confederation Identifier 108 An externally visible autonomous system number that identifies 109 a BGP confederation as a whole. 111 Member Autonomous System (Member-AS) 113 An autonomous system that is contained in a given AS 114 confederation. Note that "Member Autonomous System" and 115 "Member-AS" are used entirely interchangeably throughout 116 this document. 118 Member-AS Number 119 An autonomous system number identifier visible only within 120 a BGP confederation, and used to represent a Member-AS 121 within that confederation. 123 2. Discussion 125 It may be useful to subdivide autonomous systems with a very large 126 number of BGP speakers into smaller domains for purposes of 127 controlling routing policy via information contained in the BGP 128 AS_PATH attribute. For example, one may choose to consider all BGP 129 speakers in a geographic region as a single entity. 131 In addition to potential improvements in routing policy control, if 132 techniques such as those presented here or in [RFC 2796] are not 133 employed, [BGP-4] requires BGP speakers in the same autonomous system 134 to establish a full mesh of TCP connections among all speakers for 135 the purpose of exchanging exterior routing information. In 136 autonomous systems the number of intra-domain connections that need 137 to be maintained by each border router can become significant. 139 Subdividing a large autonomous system allows a significant reduction 140 in the total number of intra-domain BGP connections, as the 141 connectivity requirements simplify to the model used for inter-domain 142 connections. 144 Unfortunately, subdividing an autonomous system may increase the 145 complexity of routing policy based on AS_PATH information for all 146 members of the Internet. Additionally, this division increases the 147 maintenance overhead of coordinating external peering when the 148 internal topology of this collection of autonomous systems is 149 modified. 151 Therefore, division of an autonomous system into separate systems may 152 adversely affect optimal routing of packets through the Internet. 154 However, there is usually no need to expose the internal topology of 155 this divided autonomous system, which means it is possible to regard 156 a collection of autonomous systems under a common administration as a 157 single entity or autonomous system, when viewed from outside the 158 confines of the confederation of autonomous systems itself. 160 3. AS_CONFED Segment Type Extension 162 Currently, BGP specifies that the AS_PATH attribute is a well-known 163 mandatory attribute that is composed of a sequence of AS path 164 segments. Each AS path segment is represented by a triple . 167 In [BGP-4], the path segment type is a 1-octet long field with the 168 two following values defined: 170 Value Segment Type 172 1 AS_SET: unordered set of autonomous systems a route in 173 the UPDATE message has traversed 175 2 AS_SEQUENCE: ordered set of autonomous systems a route 176 in the UPDATE message has traversed 178 This document specifies two additional segment types: 180 3 AS_CONFED_SEQUENCE: ordered set of Member Autonomous 181 Systems in the local confederation that the UPDATE message 182 has traversed 184 4 AS_CONFED_SET: unordered set of Member Autonomous Systems 185 in the local confederation that the UPDATE message has 186 traversed 188 4. Operation 190 A member of a BGP confederation MUST use its AS Confederation 191 Identifier in all transactions with peers that are not members of its 192 confederation. This AS confederation identifier is the "externally 193 visible" AS number and this number is used in OPEN messages and 194 advertised in the AS_PATH attribute. 196 A member of a BGP confederation MUST use its Member-AS Number in all 197 transactions with peers that are members of the same confederation as 198 the local BGP speaker. 200 A BGP speaker receiving an AS_PATH attribute containing an autonomous 201 system matching its own AS Confederation Identifier SHALL treat the 202 path in the same fashion as if it had received a path containing its 203 own AS number. 205 A BGP speaker receiving an AS_PATH attribute containing an 206 AS_CONFED_SEQUENCE or AS_CONFED_SET which contains its own Member-AS 207 Number SHALL treat the path in the same fashion as if it had received 208 a path containing its own AS number. 210 4.1. AS_PATH Modification Rules 212 When implementing BGP Confederations Section 5.1.2 of [BGP-4] is 213 replaced with the following text: 215 When a BGP speaker propagates a route which it has learned from 216 another BGP speaker's UPDATE message, it SHALL modify the route's 217 AS_PATH attribute based on the location of the BGP speaker to which 218 the route will be sent: 220 a) When a given BGP speaker advertises the route to another BGP 221 speaker located in its own Member-AS, the advertising speaker 222 SHALL NOT modify the AS_PATH attribute associated with the 223 route. 225 b) When a given BGP speaker advertises the route to a BGP speaker 226 located in a neighboring autonomous system that is a member of 227 the local confederation, the advertising speaker SHALL update 228 the AS_PATH attribute as follows: 230 1) if the first path segment of the AS_PATH is of type 231 AS_CONFED_SEQUENCE, the local system SHALL prepend its own 232 Member-AS Number as the last element of the sequence (put 233 it in the leftmost position). 235 2) if the first path segment of the AS_PATH is not of type 236 AS_CONFED_SEQUENCE the local system SHALL prepend a new path 237 segment of type AS_CONFED_SEQUENCE to the AS_PATH, including 238 its own Member-AS Number in that segment. 240 c) When a given BGP speaker advertises the route to a BGP speaker 241 located in a neighboring autonomous system that is not a member of 242 the local confederation, the advertising speaker SHALL update the 243 AS_PATH attribute as follows: 245 1) if any path segments of the AS_PATH are of the type 246 AS_CONFED_SEQUENCE or AS_CONFED_SET, those segments MUST 247 be removed from the AS_PATH attribute, leaving the sanitized 248 AS_PATH attribute to be operated on by steps 2 or 3. 250 2) if the first path segment of the remaining AS_PATH is of type 251 AS_SEQUENCE, the local system SHALL prepend its own 252 AS Confederation Identifier as the last element of the sequence 253 (put it in the leftmost position). 255 3) if there are no path segments following the removal of the 256 first AS_CONFED_SET/AS_CONFED_SEQUENCE segments, or if the 257 first path segment of the remaining AS_PATH is not of type 258 AS_SEQUENCE the local system SHALL prepend a new path segment 259 of type AS_SEQUENCE to the AS_PATH, including its own AS 260 Confederation Identifier in that segment. 262 When a BGP speaker originates a route: 264 a) the originating speaker SHALL include an empty AS_PATH attribute 265 in all UPDATE messages sent to BGP speakers residing within the 266 same Member-AS. (An empty AS_PATH attribute is one whose length 267 field contains the value zero). 269 b) the originating speaker SHALL include its own Member-AS Number in 270 an AS_CONFED_SEQUENCE segment of the AS_PATH attribute of all 271 UPDATE messages sent to BGP speakers located in neighboring 272 Member Autonomous Systems that are members of the local 273 confederation (i.e., the originating speaker's Member-AS Number 274 will be the only entry in the AS_PATH attribute). 276 c) the originating speaker SHALL include its own AS Confederation 277 Identifier in an AS_SEQUENCE segment of the AS_PATH attribute of 278 all UPDATE messages sent to BGP speakers located in neighboring 279 autonomous systems that are not members of the local 280 confederation. (In this case, the originating speaker's AS 281 Confederation Identifier will be the only entry in the AS_PATH 282 attribute). 284 5. Error Handling 286 A BGP speaker MUST NOT transmit updates containing AS_CONFED_SET or 287 AS_CONFED_SEQUENCE attributes to peers that are not members of the 288 local confederation. 290 It is an error for a BGP speaker to receive an update message with an 291 AS_PATH attribute which contains AS_CONFED_SEQUENCE or AS_CONFED_SET 292 segments from a neighbor which is not located in the same 293 confederation. If a BGP speaker receives such an update message, it 294 SHALL treat the message as having a malformed AS_PATH according to 295 the procedures of [BGP-4] Section 6.3 ("UPDATE message error 296 handling"). 298 It is a error for a BGP speaker to receive an update message from a 299 confederation peer which is not in the same Member-AS that does not 300 have AS_CONFED_SEQUENCE as the first segment. If a BGP speaker 301 receives such an update message, it SHALL treat the message as having 302 a malformed AS_PATH according to the procedures of [BGP-4] Section 303 6.3 ("Update message error handling"). 305 5.1. Common Administrative Issues 307 It is reasonable for Member Autonomous Systems of a confederation to 308 share a common administration and IGP information for the entire 309 confederation. It is also reasonable for each Member-AS to run an 310 independent IGP. In the latter case, the NEXT_HOP may need to be set 311 using policy (i.e., by default it is unchanged). 313 5.2. MED and LOCAL_PREF Handling 315 It SHALL be legal for a BGP speaker to advertise an unchanged 316 NEXT_HOP and MULTI_EXIT_DISC (MED) attribute to peers in a 317 neighboring Member-AS of the local confederation. 319 MEDs of two routes SHOULD only be compared if the first autonomous 320 systems in the first AS_SEQUENCE in both routes are the same - i.e., 321 skip all the autonomous systems in the AS_CONFED_SET and 322 AS_CONFED_SEQUENCE. An implementation MAY provide the ability to 323 configure path selection such that MEDs of two routes are comparable 324 if the first autonomous systems in the AS_PATHs are the same, 325 regardless of AS_SEQUENCE or AS_CONFED_SEQUENCE in the AS_PATH. 327 An implementation MAY compare MEDs received from a Member-AS via 328 multiple paths. An implementation MAY compare MEDs from different 329 Member Autonomous Systems of the same confederation. 331 In addition, the restriction against sending the LOCAL_PREF attribute 332 to peers in a neighboring autonomous system within the same 333 confederation is removed. 335 5.3. AS_PATH and Path Selection 337 Path selection criteria for information received from members inside 338 a confederation MUST follow the same rules used for information 339 received from members inside the same autonomous system, as specified 340 in [BGP-4]. 342 In addition, the following rules SHALL be applied: 344 1) If the AS_PATH is internal to the local confederation (i.e., there 345 are only AS_CONFED_* segments) consider the neighbor AS to be the 346 local AS. 348 2) Otherwise, if the first segment in the path which is not an 349 AS_CONFED_SEQUENCE or AS_CONFED_SET is an AS_SEQUENCE, consider 350 the neighbor AS to be the leftmost AS_SEQUENCE AS. 352 3) When comparing routes using AS_PATH length, CONFED_SEQUENCE and 353 CONFED_SETs SHOULD NOT be counted. 355 4) When comparing routes using the internal (iBGP learned) versus 356 external (eBGP learned) rules, treat a route that is learned from 357 a peer which is in the same confederation (not necessarily the 358 same Member-AS) as "internal". 360 6. Compatability Considerations 362 All BGP speakers participating as member of a confederation MUST 363 recognize the AS_CONFED_SET and AS_CONFED_SEQUENCE segment type 364 extensions to the AS_PATH attribute. 366 Any BGP speaker not supporting these extensions will generate a 367 NOTIFICATION message specifying an "UPDATE Message Error" and a sub- 368 code of "Malformed AS_PATH". 370 This compatibility issue implies that all BGP speakers participating 371 in a confederation MUST support BGP confederations. However, BGP 372 speakers outside the confederation need not support these extensions. 374 7. Deployment Considerations 376 BGP confederations have been widely deployed throughout the Internet 377 for a number of years and are supported by multiple vendors. 379 Improper configuration of BGP confederations can cause routing 380 information within an AS to be duplicated unnecessarily. This 381 duplication of information will waste system resources, cause 382 unnecessary route flaps, and delay convergence. 384 Care should be taken to manually filter duplicate advertisements 385 caused by reachability information being relayed through multiple 386 Member Autonomous Systems based upon the topology and redundancy 387 requirements of the confederation. 389 Additionally, confederations (as well as route reflectors), by 390 excluding different reachability information from consideration at 391 different locations in a confederation, have been shown [RFC 3365] 392 cause permanent oscillation between candidate routes when using the 393 tie breaking rules required by BGP [BGP-4]. Care must be taken when 394 selecting MED values and tie breaking policy to avoid these 395 situations. 397 One potential way to avoid this is by configuring inter-Member-AS IGP 398 metrics higher than intra-Member-AS IGP metrics and/or using other 399 tie breaking policies to avoid BGP route selection based on 400 incomparable MEDs. 402 8. Security Considerations 404 This extension to BGP does not change the underlying security issues 405 inherent in the existing BGP protocol, such as those described in 406 [RFC 2385] and [BGP-VULN]. 408 9. Acknowledgments 410 The general concept of BGP confederations was taken from IDRP's 411 Routing Domain Confederations [ISO 10747]. Some of the introductory 412 text in this document was taken from [RFC 2796]. 414 The authors would like to acknowledge Bruce Cole for his 415 implementation feedback and extensive analysis of the limitations of 416 the protocol extensions described in this document and [RFC 3065]. 417 We would also like to acknowledge Srihari Ramachandra, Alex Zinin, 418 Naresh Kumar Paliwal, Jeffrey Haas, Cengiz Alaettinoglu and Bruno 419 Rijsman for their feedback and suggestions. 421 Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for 422 providing constructive and valuable feedback on earlier versions of 423 this specification. 425 10. References 427 10.1. Normative References 429 [BGP-4] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway 430 Protocol 4", Internet-Draft, "Work in Progress". 432 [RFC 1965] Traina, P. "Autonomous System Confederations for BGP", 433 RFC 1965, June 1996. 435 [RFC 3065] Traina, P., McPherson, D. and Scudder, J., "Autonomous 436 System Confederations for BGP", RFC 3065, February 2001. 438 10.2. Informative References 440 [ISO 10747] Kunzinger, C., Editor, "Inter-Domain Routing Protocol", 441 ISO/IEC 10747, October 1993. 443 [RFC 1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 444 (BGP-4)", RFC 1771, March 1995. 446 [RFC 1863] Haskin, D., "A BGP/IDRP Route Server alternative to a 447 full mesh routing", RFC 1863, October 1995. 449 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate 450 Requirement Levels", RFC 2119, March 1997. 452 [RFC 2385] Heffernan, A., "Protection of BGP Sessions via the TCP 453 MD5 Signature Option", RFC 2385, August 1998. 455 [RFC 2796] Bates, T., Chandra, R. and E. Chen, "BGP Route Reflection 456 An Alternative to Full Mesh IBGP", RFC 2796, April 2000. 458 [RFC 3365] McPherson, D., Gill, V., Walton, D., Retana, A., "Border 459 Gateway Protocol (BGP) Persistent Route Oscillation Condition", 460 RFC 3345, August 2002. 462 [BGP-VULN] Murphy, S., "BGP Security Vulnerabilities Analysis", 463 Internet-Draft, "Work in Progress". 465 11. Authors' Addresses 467 Paul Traina 468 EMail: pst+confed@spamcatcher.bogus.com 470 Danny McPherson 471 Arbor Networks, Inc. 472 Phone: +1 303.470.9257 473 EMail: danny@arbor.net 475 John G. Scudder 476 Cisco Systems, Inc. 477 170 West Tasman Drive 478 San Jose, CA 95134 479 Phone: +1 734.302.4128 480 EMail: jgs@cisco.com 482 Intellectual Property Statement 484 The IETF takes no position regarding the validity or scope of any 485 Intellectual Property Rights or other rights that might be claimed to 486 pertain to the implementation or use of the technology described in 487 this document or the extent to which any license under such rights 488 might or might not be available; nor does it represent that it has 489 made any independent effort to identify any such rights. 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