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Versions: (draft-kumari-deprecate-as-set-confed-set) 00

Network Working Group                                          W. Kumari
Internet-Draft                                              Google, Inc.
Intended status: Standards Track                               K. Sriram
Expires: March 6, 2020                                          USA NIST
                                                       September 3, 2019


             Deprecation of AS_SET and AS_CONFED_SET in BGP
             draft-ietf-idr-deprecate-as-set-confed-set-00

Abstract

   BCP 172 (i.e., RFC 6472) recommends not using AS_SET and
   AS_CONFED_SET in Border Gateway Protocol (BGP).  This document
   updates RFC 4271 and proscribes the use of the AS_SET and
   AS_CONFED_SET types of path segments in the AS_PATH.  This is done to
   simplify the design and implementation of BGP and to make the
   semantics of the originator of a route clearer.  This will also
   simplify the design, implementation, and deployment of various BGP
   security mechanisms.

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 March 6, 2020.

Copyright Notice

   Copyright (c) 2019 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



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   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
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Recommendation to Network Operators . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   BCP 172 [RFC6472] makes a recommendation for not using AS_SET and
   AS_CONFED_SET in Border Gateway Protocol (BGP).  This document
   advances the recommendation to a standards requirement in BGP.  It
   updates [RFC4271] and proscribes the use of the AS_SET and
   AS_CONFED_SET types of path segments in the AS_PATH.

   The AS_SET path segment in 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 segment
   (see [RFC5065]) in 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 combining multiple existing
   routes into a single new route.  The aggregation together with the
   use of AS_SET blurs the semantics of origin AS for the prefix being
   announced.  Therefore, the aggregation with AS_SET (or AS_CONFED_SET)
   can 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 X.509 extensions
   for IP addresses and AS identifiers [RFC3779] [RFC6811] [RFC8205].
   This in turn could result in reachability problems for the aggregated
   prefix and its components (i.e., more-specific prefixes).  The
   aggregation as described above could also create traffic engineering




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   issues, because the precise path information for the component
   prefixes are 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 Internet [Analysis] and when it is used, it is often used
   incorrectly -- reserved AS numbers ([RFC1930]) and/or only a single
   AS in the AS_SET are by far the most common cases.  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
   implementation of new BGP security technologies.

   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 aggregate
   prefix, using the exact match of the other's aggregate 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 that fell in line
   with the original intended use.  Without the use of AS_SET,
   aggregates must always contain only less-specific prefixes (not less
   than or equal to) and must never aggregate an exact match.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Recommendation to Network Operators

   Operators MUST 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 MUST withdraw those
   routes and re-announce routes for the component prefixes (i.e., the
   more-specific prefixes subsumed by the previously aggregated prefix)
   without AS_SETs or CONFED_SETs in the updates.  Route aggregation
   that was previously performed by proxy aggregation (i.e., without the
   use of AS_SETs) is still possible under some conditions.  When doing
   this, operators MUST form the aggregate at the border in the outbound
   BGP policy and omit any prefixes from the AS that the aggregate was




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   being advertised to.  As with any change, the operator should
   understand the full implications of the change.

   It is worth noting that new BGP security technologies (such as those
   that take advantage of X.509 extensions for IP addresses and AS
   identifiers [RFC3779] [RFC6811] [RFC8205]) might not support routes
   with AS_SETs/AS_CONFED_SETs in them, and may treat routes containing
   them as infeasible.  Future BGP implementations may also do the same.
   It is expected that, even before the deployment of these new or
   future technologies, operators may filter routes with AS_SETs/
   AS_CONFED_SETs in them.  Other than making that observation, this
   document is not intended to make any recommendation for how an
   implementation should behave when receiving a route with AS_SET or
   AS_CONFED_SET in it.  This document's focus is entirely on the sender
   side, as discussed in the preceding paragraph.

4.  Security Considerations

   This document obsoletes the use of aggregation techniques that create
   AS_SETs or AS_CONFED_SETs.  Obsoleting these path segment types from
   BGP and removal of the related code from implementations would
   potentially decrease the attack surface for BGP.

5.  IANA Considerations

   This document requires no IANA actions.

6.  Acknowledgements

   The authors would like to thank Tony Li, Randy Bush, John Scudder,
   Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya
   Varlashkin, 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 Hoenes, and Alvaro Retana.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.







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   [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,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

7.2.  Informative References

   [Analysis]
              Sriram, K. and D. Montgomery, "Measurement Data on AS_SET
              and AGGREGATOR: Implications for {Prefix, Origin}
              Validation Algorithms", SIDR WG presentation, IETF 78,
              July 2010, <http://www.nist.gov/itl/antd/upload/
              AS_SET_Aggregator_Stats.pdf>.

   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,
              selection, and registration of an Autonomous System (AS)",
              BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996,
              <https://www.rfc-editor.org/info/rfc1930>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <https://www.rfc-editor.org/info/rfc3779>.

   [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>.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811,
              DOI 10.17487/RFC6811, January 2013,
              <https://www.rfc-editor.org/info/rfc6811>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <https://www.rfc-editor.org/info/rfc8205>.





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Authors' Addresses

   Warren Kumari
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Phone: +1 571 748 4373
   Email: warren@kumari.net


   Kotikalapudi Sriram
   USA NIST
   100 Bureau Drive
   Gaithersburg, MD  20899
   US

   Phone: +1 301 975 3973
   Email: sriram.ietf@gmail.com































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