Network Working Group Enke Chen Internet Draft Redback Networks Expiration Date: December 2002 BGP Route Oscillation Reduction with Confederation draft-chen-confed-oscillation-reduce-00.txt 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. Abstract This document proposes a simple revision to Confederation that allows a BGP speaker in a Confederation to send a route advertisement (instead of a route withdraw) in certain cases. The availability of the routing information helps achieve stable route selection, and moves Confederation closer to IBGP full-mesh equivalence in terms of routing information. It has been shown that the proposed mechanism eliminates a number of persistent route oscillation cases involving Confederation. Chen [Page 1] Internet Draft draft-chen-confed-oscillation-reduce-00.txt June 2002 3. Introduction As documented in [1], the routing information reduction by BGP Confederation [2] can result in persistent route oscillations with certain routing setup and network topologies. This document proposes a simple revision to Confederation that allows a BGP speaker in a Confederation to send a route advertisement (instead of a route withdraw) in certain cases. The availability of the routing information helps achieve stable route selection, and moves Confederation closer to IBGP full-mesh equivalence in terms of routing information. It has been shown that the proposed mechanism eliminates a number of persistent route oscillation cases involving Confederation. The proposed mechanisms work within the current BGP protocol [4] that limits route advertisement to only one path per prefix. In addition, only the Confederation Sub-AS Border Routers need to be upgraded. One can upgrade one router at a time when required, and then immediately benefit from the route oscillation reduction or elimination. 4. Modification to Confederation Currently a BGP speaker in a Confederation [3] follows the basic BGP principle that only the best path is advertised to a BGP peer. Therefore when the overall best path for a speaker is from a peer in a neighboring AS of the same Confederation, none of the paths from peers in the same AS would be advertised by the speaker to a peer in a neighboring AS of the same Confederation, and be considered in route selection. Similarly when the overall best path for a speaker is from a peer in the same AS, none of paths from peers in a neighboring AS of the same Confederation would be advertised by the speaker to a peer in the same AS, and be considered in route selection. The following modification is proposed for Confederation: In addition to calculating the overall best path among all the received paths, a BGP speaker in a Confederation may also calculate a best path ("I-BEST") among all the paths received from peers within the same AS. It may also calculate a best path ("E-BEST") among all the paths received from peers in neighboring ASs of the same Confederation. When the I-BEST for a speaker exists, and the E-BEST is the overall best path for the speaker, the speaker may advertise the I-BEST to a peer in a neighboring AS of the Confederation. Chen [Page 2] Internet Draft draft-chen-confed-oscillation-reduce-00.txt June 2002 When the I-BEST becomes non-existence, or when it should no longer be advertised, a replacement path or route withdraw must be sent to a peer in a neighboring AS of the Confederation if an I-BEST was advertised to the peer previously. When the E-BEST for a speaker exists, and the I-BEST is the overall best path for the speaker, the speaker may advertise the E-BEST to a peer in the same AS of the Confederation. When the E-BEST becomes non-existence, or when it should no longer be advertised, a replacement path or route withdraw must be sent to a peer in the same AS if an E-BEST was advertised to the peer previously. It is noted that the advertisement of I-BEST (or E-BEST) is not useful and should not be sent when the overall best path wins over the I-BEST (or E-BEST) prior to (and including) the step of MED comparison in the route selection procedure [3, Sect. 9.1]. This modification allows additional routing information to be advertised, and be available in route selection. 5. Remarks Depending on the routing setup and network topology, the resolution of a route oscillation case may require the advertisement of either I-BEST on a router (e.g., on Rd for the case of [1, Sect 4.2]), or E- BEST on a router (e.g., on Rc and Rd for the case of [1, Sect. 5.1]), or both I-BEST and E-BEST on different routers in a network. This should be controlled via configuration. The proposed mechanism alleviates to some degree, but does not resolve the concern of routing information reduction with Confederation. Therefore the proposed mechanism may still not be adequate for certain persistent route oscillation cases in which the advertisement of multiple paths for a prefix (as proposed in [4]) may be required for their resolution. It should be noted that compared to the existing mechanism of Confederation, the proposed revision may cause memory usage in a network to increase due to the advertisement of additional routing information. Chen [Page 3] Internet Draft draft-chen-confed-oscillation-reduce-00.txt June 2002 6. Intellectual Property Considerations Redback Networks, Inc. may seek patent protection on some of the technology described in this Internet Draft. If technology in this document is adopted as a standard, Redback Networks agrees to license, on reasonable and non-discriminatory terms, any patent rights it obtains covering such technology to the extent necessary to comply with the standard. 7. Security Considerations This document introduces no new security concerns to BGP or other specifications referenced in this document. 8. Acknowledgments The author would like to thank Naiming Shen and Jenny Yuan for their review and comments. 9. References [1] McPherson, D., Gill, V., Walton, D., Retana, A., "BGP Persistent Route Oscillation Condition", Work in Progress (draft-ietf-idr- route-oscillation-01), February 2002. [2] Traina, P., McPherson, D., Scudder, J.. "Autonomous System Con- federations for BGP", RFC 3065, February 2001. [3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)", Work in Progress (draft-ietf-idr-bgp4-17), January 2002 [4] Walton, D., Cook, D., Retana, A., Scudder, J., "Advertisement of Multiple Paths in BGP", Work in Progress (draft-walton-bgp-add- paths-00), May 2002. Chen [Page 4] Internet Draft draft-chen-confed-oscillation-reduce-00.txt June 2002 10. Author Information Enke Chen Redback Networks, Inc. 350 Holger Way San Jose, CA 95134 Email: enke@redback.com Chen [Page 5]