Network Working Group                                          W. Kumari
Internet-Draft                                              Google, Inc.
Intended status: Informational                         December 29, 2010
Expires: July 2, 2011


               Deprecation of BGP AS_SET, AS_CONFED_SET.
                 draft-ietf-idr-deprecate-as-sets-01.txt

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 simpify the
   design, implementation and deployment of onging 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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 2, 2011.

Copyright Notice

   Copyright (c) 2010 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . . . 3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Deployment and modification of behavior . . . . . . . . . . . . 3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5





































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.  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 segment 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 (AS_CONFED_SETs are
   very similar to AS_SETs, but are used within a confederation).

   By performing aggregation, a router is, in essence, combining
   multiple routes into a new route.  This type of aggregation blurs the
   semantics of what it means to originate a route.  These 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 and, when it is, often contains reserved AS
   numbers ([RFC1930]) and / or only a single AS in the AS_SET.  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.


.  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].


.  Terminology

   Deprecate:  To advise against the use of a feature or function.
         Typically done before the removal of the feature or function
         from a product.


.  Deployment and modification of behavior

   Operators who are currently announcing routes containing AS_SETs or
   AS_CONFED_SETs are advised to investigate why they are doing so and
   withdraw these announcements (and possibly reannounce the network
   without the aggregation).  As with any change, the operator should
   understand the full implications of the change.




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   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.

   It is expected that, even before the deployment of these
   technologies, operators may begin filtering routers that contain
   AS_SETs or AS_CONFED_SETs.


.  IANA Considerations

   This document contains no IANA considerations.


.  Security Considerations

   By removing support for the AS_SET path segment type of the AS_PATH
   attribute future BGP implementations can be simplified.  This will
   also simplify the design and implementation of the RPKI and systems
   that will rely on it.  By removing corner cases we remove complexity
   and code that is not exercised very often, which decreases the attack
   surface.


.  Acknowledgements

   The author would like to thank Tony Li, Randy Bush, John Scudder,
   Chris Morrow, Danny McPherson, Douglas Montgomery, Enke Chen, Florian
   Weimer, Ilya Varlashkin, Jakob Heitz, John Leslie, Keyur Patel, Paul
   Jakma, Rob Austein, Russ Housley, Sandra Murphy, Sriram Kotikalapudi,
   Steve Bellovin, Steve Kent, Steve Padgett, Alfred Hones, Tom Petch,
   everyone in IDR and everyone else who provided input.

   Apologies to those who I may have missed, it was not intentional.


.  Normative 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



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              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.


Author's Address

   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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