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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT Paul Traina 4 Danny McPherson 5 Arbor Networks, Inc. 6 John Scudder 7 Cisco Systems, Inc. 8 Expires: October 2005 April 2005 10 Autonomous System Confederations for BGP 11 13 Status of this Memo 15 Status of this Memo 17 This document is an Internet-Draft and is subject to all provisions 18 of Section 3 of RFC 3667. By submitting this Internet-Draft, each 19 author represents that any applicable patent or other IPR claims of 20 which he or she is aware have been or will be disclosed, and any of 21 which he or she become aware will be disclosed, in accordance with 22 RFC 3668. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF), its areas, and its working groups. Note that 26 other groups may also distribute working documents as 27 Internet-Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt. 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html. 40 This Internet-Draft will expire on August 28, 2005. 42 Copyright Notice 44 Copyright (C) The Internet Society (2005). All Rights Reserved. 46 Abstract 48 The Border Gateway Protocol (BGP) is an inter-autonomous system 49 routing protocol designed for Transmission Control Protocol/Internet 50 Protocol (TCP/IP) networks. BGP requires that all BGP speakers 51 within a single autonomous system (AS) must be fully meshed. This 52 represents a serious scaling problem that has been well documented in 53 a number of proposals. 55 This document describes an extension to BGP which may be used to 56 create a confederation of autonomous systems that is represented as a 57 single autonomous system to BGP peers external to the confederation, 58 thereby removing the "full mesh" requirement. The intention of this 59 extension is to aid in policy administration and reduce the 60 management complexity of maintaining a large autonomous system. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 66 2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 3. AS_CONFED Segment Type Extension . . . . . . . . . . . . . . . 6 68 4. Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 4.1. AS_PATH Modification Rules. . . . . . . . . . . . . . . . . 7 70 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 8 71 5.1. Common Administrative Issues. . . . . . . . . . . . . . . . 9 72 5.2. MED and LOCAL_PREF Handling . . . . . . . . . . . . . . . . 9 73 5.3. AS_PATH and Path Selection. . . . . . . . . . . . . . . . . 10 74 6. Compatability Considerations . . . . . . . . . . . . . . . . . 10 75 7. Deployment Considerations. . . . . . . . . . . . . . . . . . . 11 76 8. Security Considerations. . . . . . . . . . . . . . . . . . . . 11 77 9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 11 78 10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 13 79 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 80 10.2. Informative References . . . . . . . . . . . . . . . . . . 13 81 11. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 14 83 1. Introduction 85 As currently defined, BGP requires that all BGP speakers within a 86 single AS must be fully meshed. The result is that for n BGP 87 speakers within an AS n*(n-1)/2 unique IBGP sessions are required. 88 This "full mesh" requirement clearly does not scale when there are a 89 large number of IBGP speakers within the autonomous system, as is 90 common in many networks today. 92 This scaling problem has been well documented and a number of 93 proposals have been made to alleviate this [RFC 1863, RFC 2796]. 94 This document presents another alternative alleviating the need for a 95 "full mesh" and is known as "Autonomous System Confederations for 96 BGP", or simply, "BGP Confederations". It has also been observed 97 that BGP Confederations may provide improvements in routing policy 98 control. 100 This document is a revision of [RFC 3065], which is itself a revision 101 to [RFC 1965]. It includes editorial changes, terminology 102 clarifications and more explicit protocol specifications based on 103 extensive implementation and deployment experience with BGP 104 Confederations. 106 1.1. Terminology 108 AS Confederation 110 A collection of autonomous systems represented and advertised 111 as a single AS number to BGP speakers that are not members of 112 the local BGP confederation. 114 AS Confederation Identifier 116 An externally visible autonomous system number that identifies 117 a BGP confederation as a whole. 119 Member Autonomous System (Member-AS) 121 An autonomous system that is contained in a given AS 122 confederation. Note that "Member Autonomous System" and 123 "Member-AS" are used entirely interchangeably throughout 124 this document. 126 Member-AS Number 127 An autonomous system number identifier visible only within 128 a BGP confederation, and used to represent a Member-AS 129 within that confederation. 131 2. Discussion 133 It may be useful to subdivide autonomous systems with a very large 134 number of BGP speakers into smaller domains for purposes of 135 controlling routing policy via information contained in the BGP 136 AS_PATH attribute. For example, one may choose to consider all BGP 137 speakers in a geographic region as a single entity. 139 In addition to potential improvements in routing policy control, if 140 techniques such as those presented here or in [RFC 2796] are not 141 employed, [BGP-4] requires BGP speakers in the same autonomous system 142 to establish a full mesh of TCP connections among all speakers for 143 the purpose of exchanging exterior routing information. In 144 autonomous systems the number of intra-domain connections that need 145 to be maintained by each border router can become significant. 147 Subdividing a large autonomous system allows a significant reduction 148 in the total number of intra-domain BGP connections, as the 149 connectivity requirements simplify to the model used for inter-domain 150 connections. 152 Unfortunately, subdividing an autonomous system may increase the 153 complexity of routing policy based on AS_PATH information for all 154 members of the Internet. Additionally, this division increases the 155 maintenance overhead of coordinating external peering when the 156 internal topology of this collection of autonomous systems is 157 modified. 159 Therefore, division of an autonomous system into separate systems may 160 adversely affect optimal routing of packets through the Internet. 162 However, there is usually no need to expose the internal topology of 163 this divided autonomous system, which means it is possible to regard 164 a collection of autonomous systems under a common administration as a 165 single entity or autonomous system, when viewed from outside the 166 confines of the confederation of autonomous systems itself. 168 3. AS_CONFED Segment Type Extension 170 Currently, BGP specifies that the AS_PATH attribute is a well-known 171 mandatory attribute that is composed of a sequence of AS path 172 segments. Each AS path segment is represented by a triple . 175 In [BGP-4], the path segment type is a 1-octet long field with the 176 two following values defined: 178 Value Segment Type 180 1 AS_SET: unordered set of autonomous systems a route in 181 the UPDATE message has traversed 183 2 AS_SEQUENCE: ordered set of autonomous systems a route 184 in the UPDATE message has traversed 186 This document specifies two additional segment types: 188 3 AS_CONFED_SEQUENCE: ordered set of Member Autonomous 189 Systems in the local confederation that the UPDATE message 190 has traversed 192 4 AS_CONFED_SET: unordered set of Member Autonomous Systems 193 in the local confederation that the UPDATE message has 194 traversed 196 4. Operation 198 A member of a BGP confederation MUST use its AS Confederation 199 Identifier in all transactions with peers that are not members of its 200 confederation. This AS confederation identifier is the "externally 201 visible" AS number and this number is used in OPEN messages and 202 advertised in the AS_PATH attribute. 204 A member of a BGP confederation MUST use its Member-AS Number in all 205 transactions with peers that are members of the same confederation as 206 the local BGP speaker. 208 A BGP speaker receiving an AS_PATH attribute containing an autonomous 209 system matching its own AS Confederation Identifier SHALL treat the 210 path in the same fashion as if it had received a path containing its 211 own AS number. 213 A BGP speaker receiving an AS_PATH attribute containing an 214 AS_CONFED_SEQUENCE or AS_CONFED_SET which contains its own Member-AS 215 Number SHALL treat the path in the same fashion as if it had received 216 a path containing its own AS number. 218 4.1. AS_PATH Modification Rules 220 When implementing BGP Confederations Section 5.1.2 of [BGP-4] is 221 replaced with the following text: 223 When a BGP speaker propagates a route which it has learned from 224 another BGP speaker's UPDATE message, it SHALL modify the route's 225 AS_PATH attribute based on the location of the BGP speaker to which 226 the route will be sent: 228 a) When a given BGP speaker advertises the route to another BGP 229 speaker located in its own Member-AS, the advertising speaker 230 SHALL NOT modify the AS_PATH attribute associated with the 231 route. 233 b) When a given BGP speaker advertises the route to a BGP speaker 234 located in a neighboring autonomous system that is a member of 235 the local confederation, the advertising speaker SHALL update 236 the AS_PATH attribute as follows: 238 1) if the first path segment of the AS_PATH is of type 239 AS_CONFED_SEQUENCE, the local system SHALL prepend its own 240 Member-AS Number as the last element of the sequence (put 241 it in the leftmost position). 243 2) if the first path segment of the AS_PATH is not of type 244 AS_CONFED_SEQUENCE the local system SHALL prepend a new path 245 segment of type AS_CONFED_SEQUENCE to the AS_PATH, including 246 its own Member-AS Number in that segment. 248 c) When a given BGP speaker advertises the route to a BGP speaker 249 located in a neighboring autonomous system that is not a member of 250 the local confederation, the advertising speaker SHALL update the 251 AS_PATH attribute as follows: 253 1) if any path segments of the AS_PATH are of the type 254 AS_CONFED_SEQUENCE or AS_CONFED_SET, those segments MUST 255 be removed from the AS_PATH attribute, leaving the sanitized 256 AS_PATH attribute to be operated on by steps 2 or 3. 258 2) if the first path segment of the remaining AS_PATH is of type 259 AS_SEQUENCE, the local system SHALL prepend its own 260 AS Confederation Identifier as the last element of the sequence 261 (put it in the leftmost position). 263 3) if there are no path segments following the removal of the 264 first AS_CONFED_SET/AS_CONFED_SEQUENCE segments, or if the 265 first path segment of the remaining AS_PATH is not of type 266 AS_SEQUENCE the local system SHALL prepend a new path segment 267 of type AS_SEQUENCE to the AS_PATH, including its own AS 268 Confederation Identifier in that segment. 270 When a BGP speaker originates a route: 272 a) the originating speaker SHALL include an empty AS_PATH attribute 273 in all UPDATE messages sent to BGP speakers residing within the 274 same Member-AS. (An empty AS_PATH attribute is one whose length 275 field contains the value zero). 277 b) the originating speaker SHALL include its own Member-AS Number in 278 an AS_CONFED_SEQUENCE segment of the AS_PATH attribute of all 279 UPDATE messages sent to BGP speakers located in neighboring 280 Member Autonomous Systems that are members of the local 281 confederation (i.e., the originating speaker's Member-AS Number 282 will be the only entry in the AS_PATH attribute). 284 c) the originating speaker SHALL include its own AS Confederation 285 Identifier in an AS_SEQUENCE segment of the AS_PATH attribute of 286 all UPDATE messages sent to BGP speakers located in neighboring 287 autonomous systems that are not members of the local 288 confederation. (In this case, the originating speaker's AS 289 Confederation Identifier will be the only entry in the AS_PATH 290 attribute). 292 5. Error Handling 294 A BGP speaker MUST NOT transmit updates containing AS_CONFED_SET or 295 AS_CONFED_SEQUENCE attributes to peers that are not members of the 296 local confederation. 298 It is an error for a BGP speaker to receive an update message with an 299 AS_PATH attribute which contains AS_CONFED_SEQUENCE or AS_CONFED_SET 300 segments from a neighbor which is not located in the same 301 confederation. If a BGP speaker receives such an update message, it 302 SHALL treat the message as having a malformed AS_PATH according to 303 the procedures of [BGP-4] Section 6.3 ("UPDATE message error 304 handling"). 306 It is a error for a BGP speaker to receive an update message from a 307 confederation peer which is not in the same Member-AS that does not 308 have AS_CONFED_SEQUENCE as the first segment. If a BGP speaker 309 receives such an update message, it SHALL treat the message as having 310 a malformed AS_PATH according to the procedures of [BGP-4] Section 311 6.3 ("Update message error handling"). 313 5.1. Common Administrative Issues 315 It is reasonable for Member Autonomous Systems of a confederation to 316 share a common administration and IGP information for the entire 317 confederation. It is also reasonable for each Member-AS to run an 318 independent IGP. In the latter case, the NEXT_HOP may need to be set 319 using policy (i.e., by default it is unchanged). 321 5.2. MED and LOCAL_PREF Handling 323 It SHALL be legal for a BGP speaker to advertise an unchanged 324 NEXT_HOP and MULTI_EXIT_DISC (MED) attribute to peers in a 325 neighboring Member-AS of the local confederation. 327 MEDs of two routes SHOULD only be compared if the first autonomous 328 systems in the first AS_SEQUENCE in both routes are the same - i.e., 329 skip all the autonomous systems in the AS_CONFED_SET and 330 AS_CONFED_SEQUENCE. An implementation MAY provide the ability to 331 configure path selection such that MEDs of two routes are comparable 332 if the first autonomous systems in the AS_PATHs are the same, 333 regardless of AS_SEQUENCE or AS_CONFED_SEQUENCE in the AS_PATH. 335 An implementation MAY compare MEDs received from a Member-AS via 336 multiple paths. An implementation MAY compare MEDs from different 337 Member Autonomous Systems of the same confederation. 339 In addition, the restriction against sending the LOCAL_PREF attribute 340 to peers in a neighboring autonomous system within the same 341 confederation is removed. 343 5.3. AS_PATH and Path Selection 345 Path selection criteria for information received from members inside 346 a confederation MUST follow the same rules used for information 347 received from members inside the same autonomous system, as specified 348 in [BGP-4]. 350 In addition, the following rules SHALL be applied: 352 1) If the AS_PATH is internal to the local confederation (i.e., there 353 are only AS_CONFED_* segments) consider the neighbor AS to be the 354 local AS. 356 2) Otherwise, if the first segment in the path which is not an 357 AS_CONFED_SEQUENCE or AS_CONFED_SET is an AS_SEQUENCE, consider 358 the neighbor AS to be the leftmost AS_SEQUENCE AS. 360 3) When comparing routes using AS_PATH length, CONFED_SEQUENCE and 361 CONFED_SETs SHOULD NOT be counted. 363 4) When comparing routes using the internal (iBGP learned) versus 364 external (eBGP learned) rules, treat a route that is learned from 365 a peer which is in the same confederation (not necessarily the 366 same Member-AS) as "internal". 368 6. Compatability Considerations 370 All BGP speakers participating as member of a confederation MUST 371 recognize the AS_CONFED_SET and AS_CONFED_SEQUENCE segment type 372 extensions to the AS_PATH attribute. 374 Any BGP speaker not supporting these extensions will generate a 375 NOTIFICATION message specifying an "UPDATE Message Error" and a sub- 376 code of "Malformed AS_PATH". 378 This compatibility issue implies that all BGP speakers participating 379 in a confederation MUST support BGP confederations. However, BGP 380 speakers outside the confederation need not support these extensions. 382 7. Deployment Considerations 384 BGP confederations have been widely deployed throughout the Internet 385 for a number of years and are supported by multiple vendors. 387 Improper configuration of BGP confederations can cause routing 388 information within an AS to be duplicated unnecessarily. This 389 duplication of information will waste system resources, cause 390 unnecessary route flaps, and delay convergence. 392 Care should be taken to manually filter duplicate advertisements 393 caused by reachability information being relayed through multiple 394 Member Autonomous Systems based upon the topology and redundancy 395 requirements of the confederation. 397 Additionally, confederations (as well as route reflectors), by 398 excluding different reachability information from consideration at 399 different locations in a confederation, have been shown [RFC 3365] 400 cause permanent oscillation between candidate routes when using the 401 tie breaking rules required by BGP [BGP-4]. Care must be taken when 402 selecting MED values and tie breaking policy to avoid these 403 situations. 405 One potential way to avoid this is by configuring inter-Member-AS IGP 406 metrics higher than intra-Member-AS IGP metrics and/or using other 407 tie breaking policies to avoid BGP route selection based on 408 incomparable MEDs. 410 8. Security Considerations 412 This extension to BGP does not change the underlying security issues 413 inherent in the existing BGP protocol, such as those described in 414 [RFC 2385] and [BGP-VULN]. 416 9. Acknowledgments 418 The general concept of BGP confederations was taken from IDRP's 419 Routing Domain Confederations [ISO 10747]. Some of the introductory 420 text in this document was taken from [RFC 2796]. 422 The authors would like to acknowledge Bruce Cole for his 423 implementation feedback and extensive analysis of the limitations of 424 the protocol extensions described in this document and [RFC 3065]. 425 We would also like to acknowledge Srihari Ramachandra, Alex Zinin, 426 Naresh Kumar Paliwal, Jeffrey Haas, Cengiz Alaettinoglu and Bruno 427 Rijsman for their feedback and suggestions. 429 Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for 430 providing constructive and valuable feedback on earlier versions of 431 this specification. 433 10. References 435 10.1. Normative References 437 [BGP-4] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway 438 Protocol 4", Internet-Draft, "Work in Progress". 440 [RFC 1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 441 (BGP-4)", RFC 1771, March 1995. 443 [RFC 1965] Traina, P. "Autonomous System Confederations for BGP", 444 RFC 1965, June 1996. 446 [RFC 3065] Traina, P., McPherson, D. and Scudder, J., "Autonomous 447 System Confederations for BGP", RFC 3065, February 2001. 449 10.2. Informative References 451 [ISO 10747] Kunzinger, C., Editor, "Inter-Domain Routing Protocol", 452 ISO/IEC 10747, October 1993. 454 [RFC 1863] Haskin, D., "A BGP/IDRP Route Server alternative to a 455 full mesh routing", RFC 1863, October 1995. 457 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate 458 Requirement Levels", RFC 2119, March 1997. 460 [RFC 2385] Heffernan, A., "Protection of BGP Sessions via the TCP 461 MD5 Signature Option", RFC 2385, August 1998. 463 [RFC 2796] Bates, T., Chandra, R. and E. Chen, "BGP Route Reflection 464 An Alternative to Full Mesh IBGP", RFC 2796, April 2000. 466 [RFC 3365] McPherson, D., Gill, V., Walton, D., Retana, A., "Border 467 Gateway Protocol (BGP) Persistent Route Oscillation Condition", 468 RFC 3345, August 2002. 470 [BGP-VULN] Murphy, S., "BGP Security Vulnerabilities Analysis", 471 Internet-Draft, "Work in Progress". 473 11. Authors' Addresses 475 Paul Traina 476 EMail: pst+confed@spamcatcher.bogus.com 478 Danny McPherson 479 Arbor Networks, Inc. 480 Phone: +1 303.470.9257 481 EMail: danny@arbor.net 483 John G. Scudder 484 Cisco Systems, Inc. 485 170 West Tasman Drive 486 San Jose, CA 95134 487 Phone: +1 734.302.4128 488 EMail: jgs@cisco.com 490 Intellectual Property Statement 492 The IETF takes no position regarding the validity or scope of any 493 Intellectual Property Rights or other rights that might be claimed to 494 pertain to the implementation or use of the technology described in 495 this document or the extent to which any license under such rights 496 might or might not be available; nor does it represent that it has 497 made any independent effort to identify any such rights. 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