Internet Engineering Task Force E. Chen Internet Draft Palo Alto Networks Updates: 4271 (if approved) S. Olofsson Intended Status: Standards Track Graphiant Inc. Expiration Date: April 19, 2022 October 18, 2021 Relax the AS Loop Detection for Aggregates in BGP draft-chen-idr-asloop-aggr-00.txt Abstract Currently an BGP aggregate may be denied or excluded by the AS loop detection mechanism when a more specific, contributing route contains the local AS number. To help enhance network robustness and simplify network operations, in this document we propose that the AS loop detection be relaxed for aggregates with an AS_SET path segment. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 19, 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as Chen & Olofsson [Page 1]
Internet Draft draft-chen-idr-asloop-aggr-00.txt October 2021 described in the Simplified BSD License. 1. Introduction As described in Section 5.1.6 of the BGP specification [RFC4271], the AS_SET path segment is formed when aggregating several routes, and it normally includes the set of ASes from which the aggregate was formed. The aggregate, being less specific than the contributing routes, is different from any of the more specific, contributing routes, and is a new route for all practical purposes. When an aggregate is propagated through the routing system, it may land in a network that has contributed with a more specific route to the aggregate and thus has its AS number present in the AS_SET path segment of the AS_PATH attribute. The aggregate may be denied, or be excluded in BGP route selection due to the AS loop detection mechanism specified in Section 9.1.2 [RFC4271]: If the AS_PATH attribute of a BGP route contains an AS loop, the BGP route should be excluded from the Phase 2 decision function. AS loop detection is done by scanning the full AS path (as specified in the AS_PATH attribute), and checking that the autonomous system number of the local system does not appear in the AS path. Operations of a BGP speaker that is configured to accept routes with its own autonomous system number in the AS path are outside the scope of this document. By dropping the aggregate, or excluding it in BGP route selection when the local AS is contained in the AS_SET, one can lose reachability, in particular when only the aggregate is advertised and the more specific contributing routes are suppressed. Although BCP 172 [RFC6472] makes a recommendation for not using the AS_SET path segment in BGP, the AS_SET path segment may remain in use for a long time. To help enhance network robustness and simplify network operations, in this document we propose that the AS loop detection be relaxed for aggregates with an AS_SET path segment. Chen & Olofsson [Page 2]
Internet Draft draft-chen-idr-asloop-aggr-00.txt October 2021 2. Revision to AS Loop Detection The AS loop detection specified in Section 9.1.2. of [RFC4271] is revised as follows: Old text: AS loop detection is done by scanning the full AS path (as specified in the AS_PATH attribute), and checking that the autonomous system number of the local system does not appear in the AS path. New text: AS loop detection is done by scanning the full AS path (as specified in the AS_PATH attribute) but excluding the AS path segments with the AS_SET segment type, and checking that the autonomous system number of the local system does not appear in the AS path. 3. IANA Considerations This document makes no request to IANA. 4. Security Considerations The revision proposed in this document does not change the underlying security or confidentiality issues inherent in the existing BGP [RFC4271]. 5. Acknowledgments TBD. Chen & Olofsson [Page 3]
Internet Draft draft-chen-idr-asloop-aggr-00.txt October 2021 6. References 6.1. Normative References [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <http://www.rfc-editor.org/info/rfc4271>. 6.2. Informative References [RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472, DOI 10.17487/RFC6472, December 2011, <https://www.rfc-editor.org/info/rfc6472>. 7. Authors' Addresses Enke Chen Palo Alto Networks, Inc. Email: enchen@paloaltonetworks.com Stefan Olofsson Graphiant Inc. Email: stefan@Graphiant.com Chen & Olofsson [Page 4]