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Recommendation to avoid use of BGP Extended Communities at Internet Exchange Route Servers
draft-ietf-grow-ixp-ext-comms-00

Document Type Active Internet-Draft (grow WG)
Authors Job Snijders , Stavros Konstantaras , Mo Shivji
Last updated 2024-06-05
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draft-ietf-grow-ixp-ext-comms-00
Global Routing Operations                                    J. Snijders
Internet-Draft                                                    Fastly
Intended status: Best Current Practice                   S. Konstantaras
Expires: 6 December 2024                                          AMS-IX
                                                               M. Shivji
                                                                    LINX
                                                             4 June 2024

  Recommendation to avoid use of BGP Extended Communities at Internet
                         Exchange Route Servers
                    draft-ietf-grow-ixp-ext-comms-00

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.

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
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   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 6 December 2024.

Copyright Notice

   Copyright (c) 2024 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.

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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Recommendation  . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

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.

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.  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.

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   Use of Extended Communities arose from a lack of support to fit
   4-octet Autonomous System Numbers (ASNs) [RFC4893] in 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.
   Since the introduction of BGP Large communities in 2017 - by now -
   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, any efforts that minimize the number of BGP UPDATE
   messages are advantageous for the routing system.  The authors of
   this document posit that Extended Communities are superfluous in
   context of the existence of Large Communities.

4.  Recommendation

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

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   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.  Acknowledgments

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

6.  Security Considerations

   There are no security considerations accompanying this document.

7.  IANA Considerations

   This document has no actions for IANA.

8.  References

8.1.  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>.

   [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>.

8.2.  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>.

   [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>.

   [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
   Fastly, Inc.
   Amsterdam
   Netherlands
   Email: job@fastly.com

   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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