Guidance to Avoid Use of BGP Extended Communities at Internet Exchange Route Servers
draft-ietf-grow-ixp-ext-comms-03

Global Routing Operations                                    J. Snijders
Internet-Draft                                                       BSD
Updates: 7948 (if approved)                              S. Konstantaras
Intended status: Best Current Practice                            AMS-IX
Expires: 12 June 2026                                          M. Shivji
                                                                    LINX
                                                         9 December 2025

 Guidance to Avoid Use of BGP Extended Communities at Internet Exchange
                             Route Servers
                    draft-ietf-grow-ixp-ext-comms-03

Abstract

   This document outlines a recommendation to the Internet operational
   community to avoid the use of BGP Extended Communities at Internet
   Exchange Point (IXP) Route Servers.  It includes guidance for both
   the Internet Service Provider side peering with Route Servers and
   IXPs operating Route Servers.  This recommendation aims to help the
   global Internet routing system's performance and help protect Route
   Server participants against misconfigurations.  This document updates
   RFC 7948.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 12 June 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Recommendation  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Changes to RFC7948  . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document outlines a recommendation to the Internet operational
   community to avoid the use of BGP Extended Communities [RFC4360] at
   Internet Exchange Point (IXP) Route Servers [RFC7947], [RFC7948].  It
   includes guidance for both the Internet Service Provider side peering
   with Route Servers and IXPs operating Route Servers.  This
   recomendation aims to help the global Internet routing system's
   performance and help protect Route Server participants against
   misconfigurations.  This document updates [RFC7948].

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.

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3.  Background

   The main use-case for Extended Communities are as Route Targets
   within VPN [RFC4364] deployments, but historically Extended
   Communities also have been used as an operational utility to signal
   requests to IXP Route Servers such as functionality to reduce
   propagation scope or request AS_PATH prepending.

   The practise of using Extended Communities arose from the inability
   to fit 4-octet Autonomous System Numbers (ASNs) [RFC4893] in the
   fields of Classic BGP communities [RFC1997], thus operators
   improvised a method that could allow BGP signaling from IXP
   participants with 4-octet ASN.  The 6-octet space for the Global and
   Local administrator part of the BGP Extended Community provides
   sufficient space for a single 4-octet ASN.  However, the 6-octet
   space is not sufficient enough should a 4-octet ASN participant of an
   IXP want to send a signal to a 4-octet ASN Route Server or to another
   4-octet ASN participant.  Moreover, the flexibility to insert a
   4-octet ASN either in the Global or the Local Administrator part,
   proved to bring extra complexity both in the BGP implementations and
   in the route propagation functions that are being triggered through
   BGP Extended Communities.  Although, this method was widely
   considered to be an acceptable workaround for a period of time, a
   more robust and future proof solution was needed that could overcome
   the aforementioned obstacles.

   BGP Large communities [RFC8092] addressed the operational
   requirements for working with 4-octet ASNs in a variety of scenarios.
   With a total space of 12 octets divided into 3 separate fields,
   signalling between 2-octet ASNs and 4-octet ASNs, or 4-octet ASNs and
   4-octet ASNs, making the use of BGP Extended Communities redundant.
   As of May 2025, virtually all BGP implementations have adopted this
   standard, making this feature usable in all public Internet
   deployments.

   At the moment of writing this recommendation, there are still IP
   Network and IXP operators that support BGP Extended Communities for
   IXP Route Server signaling purposes.  However, supporting three
   flavors of BGP Communities (Classic, Large, and Extended) contribute
   to increased memory consumption, increased complexity in Routing
   Policies, and reduced stability of the Internet ecosystem as BGP
   speakers need to send a BGP UPDATE message every time any type of BGP
   Community is added, removed, or modified.  As each and every BGP
   UPDATE message propagated and received requires CPU cycles for
   processing, all efforts that minimize the number of BGP UPDATE
   messages are advantageous for the routing system.  In this context,
   Extended Communities are now considered superfluous because of the
   existence of Large Communities.

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4.  Recommendation

   Route Server operators that currently match on route announcements
   with Extended Communities for 4-octet ASNs SHOULD replace these
   configurations with equivalent functionality implemented using Large
   Communities [RFC8092].

   As an additional recommendation, Route Server operators should
   communicate a clear timeline for their clients to transition from
   Extended to Large communities.

   Finally, operators of Internet Exchange Route Servers are RECOMMENDED
   to:

   *  Scrub the BGP Extended Communities at the inbound direction which
      are intendend for L3VPN purposes.  That concerns the Extended
      communities where the sub-type value has been set to 0x02 (Route
      Target).

   *  Allow the rest of the BGP Extended Communities to transit
      transparently through the Route Servers.

5.  Changes to RFC7948

   This document updates Section 4.6.1 of [RFC7948] to replace all
   occurrences of BGP Extended Communities with BGP Large Communities.

   OLD:
      Prefixes sent to the route server are tagged with specific
      standard BGP Communities [RFC1997] or Extended Communities
      [RFC4360] attributes, based on predefined values agreed between
      the operator and all clients.

   NEW:
      Prefixes sent to the route server are tagged with specific
      standard BGP Communities [RFC1997] or BGP Large Communities
      [RFC8092] attributes, based on predefined values agreed between
      the operator and all clients.

   OLD:
      As both standard BGP Communities and Extended Communities values
      are restricted to 6 octets or fewer, it is not possible for both
      the global and local administrator fields in the BGP Communities
      value to fit a 4-octet AS number.

   NEW:

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      As a standard BGP Communities value is restricted to a total of 4
      octets, it is not possible for both the global and local
      administrator fields in the BGP Communities value to fit a 4-octet
      AS number.

   The Informative Reference to [RFC4360] in [RFC7948] is replaced with
   an Informative Reference to [RFC8092].

6.  Acknowledgments

   The authors would like to thank Jeffrey Haas, Nick Hilliard and
   Martin Pels for their useful feedback and suggestions during the
   review process through the GROW mailing list.

7.  Security Considerations

   There are no security considerations accompanying this document.

8.  IANA Considerations

   This document has no actions for IANA.

9.  References

9.1.  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>.

   [RFC7948]  Hilliard, N., Jasinska, E., Raszuk, R., and N. Bakker,
              "Internet Exchange BGP Route Server Operations", RFC 7948,
              DOI 10.17487/RFC7948, September 2016,
              <https://www.rfc-editor.org/info/rfc7948>.

   [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>.

9.2.  Informative References

   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities
              Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
              <https://www.rfc-editor.org/info/rfc1997>.

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   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <https://www.rfc-editor.org/info/rfc4360>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007,
              <https://www.rfc-editor.org/info/rfc4893>.

   [RFC7947]  Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
              "Internet Exchange BGP Route Server", RFC 7947,
              DOI 10.17487/RFC7947, September 2016,
              <https://www.rfc-editor.org/info/rfc7947>.

   [RFC8092]  Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
              I., and N. Hilliard, "BGP Large Communities Attribute",
              RFC 8092, DOI 10.17487/RFC8092, February 2017,
              <https://www.rfc-editor.org/info/rfc8092>.

Authors' Addresses

   Job Snijders
   BSD Software Development
   Amsterdam
   Netherlands
   Email: job@bsd.nl
   URI:   https://www.bsd.nl/

   Stavros Konstantaras
   Amsterdam Internet Exchange
   Amsterdam
   Netherlands
   Email: stavros.konstantaras@ams-ix.net

   Mo Shivji
   London Internet Exchange Ltd
   London
   United Kingdom
   Email: moyaze@linx.net

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