idnits 2.17.1 draft-ietf-idr-route-oscillation-stop-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (April 11, 2016) is 2937 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-15) exists of draft-ietf-idr-add-paths-13 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Walton 3 Internet-Draft Cumulus Networks 4 Intended status: Standards Track A. Retana 5 Expires: October 13, 2016 E. Chen 6 Cisco Systems, Inc. 7 J. Scudder 8 Juniper Networks 9 April 11, 2016 11 BGP Persistent Route Oscillation Solutions 12 draft-ietf-idr-route-oscillation-stop-02 14 Abstract 16 This document presents two sets of paths for an address prefix that 17 can be advertised by a BGP route reflector or confederation ASBR to 18 eliminate the MED-induced route oscillations in a network. The first 19 set involves all the available paths, and would achieve the same 20 routing consistency as the full IBGP mesh. The second set, which is 21 a subset of the first one, involves the neighbor-AS based Group Best 22 Paths, and would be sufficient to eliminate the MED-induced route 23 oscillations (subject to certain commonly adopted topological 24 constrains). 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on October 13, 2016. 43 Copyright Notice 45 Copyright (c) 2016 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 62 3. Advertise the Available Paths . . . . . . . . . . . . . . . . 3 63 4. Advertise the Group Best Paths . . . . . . . . . . . . . . . 4 64 5. Route Reflection and Confederation . . . . . . . . . . . . . 4 65 5.1. Route Reflection . . . . . . . . . . . . . . . . . . . . 5 66 5.2. Confederation . . . . . . . . . . . . . . . . . . . . . . 5 67 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 68 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 69 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 70 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 71 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 73 10.2. Informative References . . . . . . . . . . . . . . . . . 7 74 Appendix A. Why the Group Best Paths Are Adequate? . . . . . . . 7 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 77 1. Introduction 79 As documented in [RFC3345], the routing information reduction by BGP 80 Route Reflection [RFC4456] or BGP Confederation [RFC5065] can result 81 in persistent IBGP route oscillations with certain routing setup and 82 network topologies. Except for a couple artificially engineered 83 network topologies, the MED attribute [RFC4271] has played a pivotal 84 role in virtually all of the known persistent IBGP route 85 oscillations. For the sake of brevity, we use the term "MED-induced 86 route oscillation" hereafter to refer to a persistent IBGP route 87 oscillation in which the MED plays a role. 89 In order to eliminate the MED-induced route oscillations and to 90 achieve consistent routing in a network, clearly a route reflector or 91 a confederation ASBR needs to advertise more than just the best path 92 for an address prefix. Our goal is to identify the "right" set of 93 paths for an address prefix that needs to be advertised by a route 94 reflector or a confederation ASBR. 96 In this document we present two sets of paths for an address prefix 97 that can be advertised by a BGP route reflector or confederation ASBR 98 to eliminate the MED-induced route oscillations in a network. The 99 first set involves all the available paths, and would achieve the 100 same routing consistency as the full IBGP mesh. The second set, 101 which is a subset of the first one, involves the neighbor-AS based 102 Group Best Paths, and would be sufficient to eliminate the MED- 103 induced route oscillations (subject to certain commonly adopted 104 topological constrains). 106 These paths can be advertised using the mechanism described in ADD- 107 PATH [I-D.ietf-idr-add-paths] for advertising multiple paths. No 108 other assumptions in functionality beyond the base BGP specification 109 [RFC4271] is assumed. 111 2. Requirements Language 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 115 document are to be interpreted as described in [RFC2119]. 117 3. Advertise the Available Paths 119 Observe that in a network that maintains a full IBGP mesh all the BGP 120 speakers have consistent and equivalent routing information. Such a 121 network is thus free of the MED-induced route oscillations and other 122 routing inconsistencies such as forwarding loops. 124 Therefore one approach is to allow a route reflector or a 125 confederation ASBR to advertise all the available paths for an 126 address prefix. Clearly this approach would yield the same amount of 127 routing information and achieve the same routing consistency as the 128 full IBGP mesh in a network. 130 This approach can be implemented using the mechanism described in 131 ADD-PATH [I-D.ietf-idr-add-paths] for advertising multiple paths for 132 certain prefixes. 134 For the sake of scalability the advertisement of multiple paths 135 should be limited to those prefixes which are affected by MED-induced 136 route oscillation in a network carrying a large number of alternate 137 paths. A detailed description of how these oscillations can occur 138 can be found in [RFC3345]; the description of how a node would 139 locally detect such condition is outside the scope of this document. 141 4. Advertise the Group Best Paths 143 The term neighbor-AS for a route refers to the neighboring AS from 144 which the route was received. The calculation of the neighbor-AS is 145 specified in Section 9.1.2.2 of [RFC4271], and Section 7.2 of 146 [RFC5065]. By definition the MED is comparable only among routes 147 with the same neighbor-AS. Thus the route selection procedures 148 specified in [RFC4271] would conceptually involve two steps: first 149 organize the paths for an address prefix into groups according to 150 their respective neighbor-AS's, and calculate the most preferred one 151 (termed "Group Best Path") for each of the groups; Then calculate the 152 overall best path among all the Group Best Paths. 154 As a generally recommended ([RFC4456], [RFC5065]) and widely adopted 155 practice, a route reflection cluster or a confederation sub-AS should 156 be designed such that the IGP metrics for links within a cluster (or 157 confederation sub-AS) are much smaller than the IGP metrics for the 158 links between the clusters (or confederation sub-AS). This practice 159 helps achieve consistent routing within a route reflection cluster or 160 a confederation sub-AS. 162 When the aforementioned practice for devising a route reflection 163 cluster or confederation sub-AS is followed in a network, we claim 164 that the advertisement of all the Group Best Paths by a route 165 reflector or a confederation ASBR is sufficient to eliminate the MED- 166 induced route oscillations in the network. This claim is validated 167 in Appendix A. 169 Note that a Group Best Path for an address prefix can be identified 170 by the combination of the address prefix and the neighbor-AS. Thus 171 this approach can be implemented using the mechanism described in 172 ADD-PATH [I-D.ietf-idr-add-paths] for advertising multiple paths, and 173 in this case the neighbor-AS of a path may be used as the path 174 identifier of the path. 176 It should be noted that the approach of advertising the Group Best 177 Paths requires certain topological constrains to be satisfied in 178 order to eliminate the MED-induced route oscillation. Specific 179 topological considerations are described in [RFC3345]. 181 5. Route Reflection and Confederation 183 To allow a route reflector or a confederation ASBR to advertise 184 either the Available Paths or Group Best Paths using the mechanism 185 described in ADD-PATH [I-D.ietf-idr-add-paths], the following 186 revisions are proposed for BGP route reflection and BGP 187 Confederation. 189 5.1. Route Reflection 191 Depending on the configuration, for a particular a route 192 reflector SHOULD include the with the "Send/Receive" 193 field set to 2 (send multiple paths) or 3 (send/receive multiple 194 paths) in the ADD-PATH Capability [I-D.ietf-idr-add-paths] advertised 195 to an IBGP peer. When the ADD-PATH Capability is also received from 196 the IBGP peer with the "Send/Receive" field set to 1 (receive 197 multiple paths) or 3 (send/receive multiple paths) for the same , then the following procedures shall be followed: 200 If the peer is a route reflection client, the route reflector SHOULD 201 advertise to the peer the Group Best Paths (or the Available Paths) 202 received from its non-client IBGP peers. Depending on the 203 configuration, the route reflector MAY also advertise to the peer the 204 Group Best Paths (or the Available Paths) received from its clients. 206 If the peer is a non-client, the route reflector SHOULD advertise to 207 the peer the Group Best Paths (or the Available Paths) received from 208 its clients. 210 5.2. Confederation 212 Depending on the configuration, for a particular a 213 confederation ASBR SHOULD include the with the "Send/ 214 Receive" field set to 2 (send multiple paths) or 3 (send/receive 215 multiple paths) in the ADD-PATH Capability [I-D.ietf-idr-add-paths] 216 advertised to an IBGP peer, and to a confederation external peer. 217 When the ADD-PATH Capability is also received from the IBGP peer or 218 the confederation external peer with the "Send/Receive" field set to 219 1 (receive multiple paths) or 3 (send/receive multiple paths) for the 220 same , then the following procedures shall be followed: 222 If the peer is internal, the confederation ASBR SHOULD advertise to 223 the peer the Group Best Paths (or the Available Paths) received from 224 its confederation external peers. 226 If the peer is confederation external, the confederation ASBR SHOULD 227 advertise to the peer the Group Best Paths (or the Available Paths) 228 received from its IBGP peers. 230 6. Deployment Considerations 232 Some route oscillations, once detected, can be eliminated by simple 233 configuration workarounds. As carrying additional paths impacts the 234 memory usage and routing convergence in a network, it is recommended 235 that the impact be evaluated and the approach of using a 236 configuration workaround be considered in deciding whether to deploy 237 the proposed mechanism in a network. In addition, the advertisement 238 of multiple paths should be limited to those prefixes which are 239 affected by MED-induced route oscillation. 241 While the route reflectors or confederation ASBRs in a network need 242 to advertise the Group Best Paths or Available Paths, the vast 243 majority of the BGP speakers in the network only need to receive the 244 Group Best Paths or Available Paths, which would involve only minor 245 software changes. 247 It should be emphasized that in order to eliminate the MED-induced 248 route oscillations in a network using the approach of advertising the 249 Group Best Paths, the recommended practice for devising a route 250 reflection cluster or confederation sub-AS with respect to the IGP 251 metrics ([RFC4456], [RFC5065]) should be followed. 253 It is expected that the approach of advertising the Group Best Paths 254 would be adequate to achieve consistent routing for the vast majority 255 of the networks. For a network that has large number of alternate 256 paths, the approach should be a good choice as the number of paths 257 advertised by a reflector or a confederation ASBR is bounded by the 258 number of the neighbor-AS's for a particular address prefix. The 259 additional states for an address prefix would also be per neighbor-AS 260 based rather than per path based. The number of the neighbor-AS's 261 for a particular address prefix is typically small because of the 262 limited number of upstream providers for a customer and the nature of 263 advertising only customer routes at the inter-exchange points. 265 The approach of advertising the Group Best Paths, however, may still 266 be inadequate for certain networks to avoid other routing 267 inconsistencies such as forwarding loops. The required topological 268 constrains could also be operationally challenging. In these cases 269 the approach of advertising the Available Paths may be used, but 270 should be limited to those prefixes which are affected by MED-induced 271 route oscillation in a network carrying a large number of alternate 272 paths. Note that the number of paths that need to be maintained and 273 advertised can be greatly reduced by accepting MEDs from other 274 peering networks. 276 7. IANA Considerations 278 This memo includes no request to IANA. 280 8. Security Considerations 282 This extension to BGP does not change the underlying security issues 283 inherent in the existing BGP [RFC4271]. 285 9. Acknowledgements 287 We would like to thank David Cook and Naiming Shen for their 288 contributions to the design and development of the solutions. 290 10. References 292 10.1. Normative References 294 [I-D.ietf-idr-add-paths] 295 Walton, D., Retana, A., Chen, E., and J. Scudder, 296 "Advertisement of Multiple Paths in BGP", draft-ietf-idr- 297 add-paths-13 (work in progress), December 2015. 299 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 300 Requirement Levels", BCP 14, RFC 2119, 301 DOI 10.17487/RFC2119, March 1997, 302 . 304 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 305 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 306 DOI 10.17487/RFC4271, January 2006, 307 . 309 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route 310 Reflection: An Alternative to Full Mesh Internal BGP 311 (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, 312 . 314 [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous 315 System Confederations for BGP", RFC 5065, 316 DOI 10.17487/RFC5065, August 2007, 317 . 319 10.2. Informative References 321 [RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana, 322 "Border Gateway Protocol (BGP) Persistent Route 323 Oscillation Condition", RFC 3345, DOI 10.17487/RFC3345, 324 August 2002, . 326 Appendix A. Why the Group Best Paths Are Adequate? 328 It is assumed that the following common practice is followed. A 329 route reflection cluster or a confederation sub-AS should be designed 330 such that the IGP metrics for links within a cluster (or 331 confederation sub-AS) are much smaller than the IGP metrics for the 332 links between the clusters (or confederation sub-AS). This practice 333 helps achieve consistent routing within a route reflection cluster or 334 a confederation sub-AS. 336 Observe that in a network that maintains full IBGP mesh only the 337 paths that survive the (Local_Pref, AS-PATH Length, Origin, MED) 338 comparisons [RFC4271] would contribute to the route selection in the 339 network. 341 Consider a route reflection cluster that sources one or more paths 342 that would survive the (Local_Pref, AS-PATH Length, Origin, MED) 343 comparisons among all the paths in the network. One of these 344 surviving paths would be selected as the Group Best Path by the route 345 reflector in the cluster. Due to the constrain on the IGP metrics as 346 described previously, this path would remain as the Group Best Path 347 and would be advertised to all other clusters even after a path is 348 received from another cluster. 350 On the other hand, when no path in a route reflection cluster would 351 survive the (Local_Pref, AS-PATH Length, Origin, MED) comparisons 352 among all the paths in the network, the Group Best Path (when exists) 353 for a route reflector would be from another cluster. Clearly the 354 advertise of the Group Best Path by the route reflector to the 355 clients only depends on the paths received from other clusters. 357 Therefore there is no MED-induced route oscillation in the network as 358 the advertisement of a Group Best Path to a peer does not depend on 359 the paths received from that peer. 361 The claim for the confederation can be validated similarly. 363 Authors' Addresses 365 Daniel Walton 366 Cumulus Networks 367 140C S. Whisman Rd. 368 Mountain View, CA 94041 369 USA 371 Email: dwalton@cumulusnetworks.com 373 Alvaro Retana 374 Cisco Systems, Inc. 375 7025 Kit Creek Rd. 376 Research Triangle Park, NC 27709 377 USA 379 Email: aretana@cisco.com 380 Enke Chen 381 Cisco Systems, Inc. 382 170 W. Tasman Dr. 383 San Jose, CA 95134 384 USA 386 Email: enkechen@cisco.com 388 John Scudder 389 Juniper Networks 390 1194 N. Mathilda Ave 391 Sunnyvale, CA 94089 392 USA 394 Email: jgs@juniper.net