Internet Engineering Task Force (IETF) W. Kumari
Request for Comments: 6472 Google, Inc.
BCP: 172 K. Sriram
Category: Best Current Practice U.S. NIST
ISSN: 2070-1721 December 2011
Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP
Abstract
This document recommends against the use of the AS_SET and
AS_CONFED_SET types of the AS_PATH in BGPv4. This is done to
simplify the design and implementation of BGP and to make the
semantics of the originator of a route more clear. This will also
simplify the design, implementation, and deployment of ongoing work
in the Secure Inter-Domain Routing Working Group.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6472.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Kumari & Sriram Best Current Practice [Page 1]
RFC 6472 AS_SET, AS_CONFED_SET Use Deprecation December 2011
Table of Contents
1. Introduction ....................................................2
2. Requirements Notation ...........................................3
3. Recommendation to Network Operators .............................3
4. Security Considerations .........................................4
5. Acknowledgements ................................................4
6. References ......................................................4
6.1. Normative References .......................................4
6.2. Informative References .....................................4
1. Introduction
The AS_SET path segment type of the AS_PATH attribute (Sections 4.3
and 5.1.2 of [RFC4271]) is created by a router that is performing
route aggregation and contains an unordered set of Autonomous Systems
(ASes) that the update has traversed. The AS_CONFED_SET path type
([RFC5065]) of the AS_PATH attribute is created by a router that is
performing route aggregation and contains an unordered set of Member
AS Numbers in the local confederation that the update has traversed.
It is very similar to AS_SETs but is used within a confederation.
By performing aggregation, a router is, in essence, combining
multiple existing routes into a single new route. This type of
aggregation blurs the semantics of what it means to originate a
route. Said aggregation can therefore cause operational issues, such
as not being able to authenticate a route origin for the aggregate
prefix in new BGP security technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" [RFC3779]). This in turn would result in reachability
problems for the aggregated prefix and its components (i.e., more
specifics). Said aggregation also creates traffic engineering
issues, because the precise path information for the component
prefixes is not preserved.
From analysis of past Internet routing data, it is apparent that
aggregation that involves AS_SETs is very seldom used in practice on
the public network [Analysis] and, when it is used, it is usually
used incorrectly -- reserved AS numbers ([RFC1930]) and/or only a
single AS in the AS_SET are by far the most common case. Because the
aggregation involving AS_SETs is very rarely used, the reduction in
table size provided by said aggregation is extremely small, and any
advantage thereof is outweighed by additional complexity in BGP. As
noted above, said aggregation also poses impediments to
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