Network Working Group W. Kumari
Internet-Draft Google, Inc.
Intended status: BCP K. Sriram
Expires: January 28, 2012 U.S. NIST
July 27, 2011
Deprecation of the use of BGP AS_SET, AS_CONFED_SET.
draft-ietf-idr-deprecate-as-sets-05
Abstract
This document deprecates 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 the BGP protocol 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 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
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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 January 28, 2012.
Copyright Notice
Copyright (c) 2011 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3
3. Recommendation to Network Operators . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
7. Informative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
The AS_SET path segment type of the AS_PATH attribute ([RFC4271],
Section 4.3) is created by a router that is performing route
aggregation and contains an unordered set of ASs 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
which can cause operational issues that include reachability problems
and traffic engineering issues.
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. The
reduction in table size provided by the aggregation is outweighed by
additional complexity in the BGP protocol and confusion regarding
what exactly is meant by originating a route.
In the past AS_SET had been used in a few rare cases to allow route
aggregation where two or more providers could form the same prefix,
using the exact match of the others prefix in some advertisement and
configuring the aggregation differently elsewhere. The key to
configuring this correctly was to form the aggregate at the border in
the outbound BGP policy and omit prefixes from the AS that the
aggregate was being advertised to. The AS_SET therefore allowed this
practice without the loss of BGP's AS_PATH loop protection. This use
of AS_SET served a purpose which fell in line with the original
intended use.
Without AS_SET aggregates must always contain only less specific
prefixes (not less than or equal to), and must never aggregate an
exact match. Since this practice is thought to no longer be widely
used, it is thought to be safe to deprecate the use of AS_SET.
2. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Recommendation to Network Operators
Operators are strongly advised to not generate any new announcements
containing AS_SETs or AS_CONFED_SETs. If they have already announced
routes with AS_SETs or AS_CONFED_SETs in them, then they should
withdraw and re-announce those prefixes without AS_SETs in the
updates. This may require undoing the aggregation that was
previously performed, and announcing more specifics. Route
aggregation that was previously performed by proxy aggregation is
still possible under some conditions without the use of AS_SETs. As
with any change, the operator should understand the full implications
of the change.
It is worth noting that new technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" ([RFC3779]) may not support routes with AS_SETs /
AS_CONFED_SETs in them, and MAY treat as infeasible routes containing
them. Future BGP implementations may also do the same.
It is expected that, even before the deployment of these
technologies, operators may begin filtering routes that contain
AS_SETs or AS_CONFED_SETs.
4. IANA Considerations
This document requires no IANA actions.
5. Security Considerations
This document discourages the use of aggregation techniques that
create AS_SETs. Future work may update the protocol to remove
support for the AS_SET path segment type of the AS_PATH attribute.
This will remove complexity and code that is not exercised very
often, which decreases the attack surface. This will also simplify
the design and implementation of the RPKI and systems that will rely
on it.
6. Acknowledgements
The authors would like to thank Tony Li, Randy Bush, John Scudder,
Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya
Varlashkin as well as Douglas Montgomery, Enke Chen, Florian Weimer,
Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ
Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett,
Alfred Hones, Alvaro Retana, everyone in IDR and everyone else who
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provided input
Apologies to those who we may have missed, it was not intentional.
7. Informative References
[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)",
BCP 6, RFC 1930, March 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065, August 2007.
[analysis]
Sriram, K., "Measurement Data on AS_SET and AGGREGATOR,
SIDR WG presentation, IETF-78", July 2010, < http://
www.antd.nist.gov/~ksriram/AS_SET_Aggregator_Stats.pdf>.
Authors' Addresses
Warren Kumari
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Phone: +1 571 748 4373
Email: warren@kumari.net
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Kotikalapudi Sriram
U.S. NIST
100 Bureau Drive
Gaithersburg, MD 20899
US
Phone: +1 301 975 3973
Email: ksriram@nist.gov
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