Internet DRAFT - draft-chen-idr-asloop-aggr
draft-chen-idr-asloop-aggr
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
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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.
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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.
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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
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