





Internet Engineering Task Force (IETF)                     J. Heitz, Ed.
Request for Comments: 8092                                         Cisco
Category: Standards Track                               J. Snijders, Ed.
ISSN: 2070-1721                                                      NTT
                                                                K. Patel
                                                                  Arrcus
                                                             I. Bagdonas
                                                                 Equinix
                                                             N. Hilliard
                                                                    INEX
                                                           February 2017


                    BGP Large Communities Attribute

Abstract

   This document describes the BGP Large Communities attribute, an
   extension to BGP-4.  This attribute provides a mechanism to signal
   opaque information within separate namespaces to aid in routing
   management.  The attribute is suitable for use with all Autonomous
   System Numbers (ASNs) including four-octet ASNs.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8092.















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Copyright Notice

   Copyright (c) 2017 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
   (http://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
   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. BGP Large Communities Attribute .................................3
   4. Aggregation .....................................................4
   5. Canonical Representation ........................................4
   6. Error Handling ..................................................5
   7. Security Considerations .........................................5
   8. IANA Considerations .............................................6
   9. References ......................................................6
      9.1. Normative References .......................................6
      9.2. Informative References .....................................6
   Acknowledgments ....................................................7
   Contributors .......................................................7
   Authors' Addresses .................................................8

1.  Introduction

   BGP [RFC4271] implementations typically support a routing policy
   language to control the distribution of routing information.  Network
   operators attach BGP communities to routes to associate particular
   properties with these routes.  These properties may include
   information such as the route origin location, or specification of a
   routing policy action to be taken, or one that has been taken, and is
   applied to all routes contained in a BGP Update Message where the
   Communities Attribute is included.  Because BGP communities are
   optional transitive BGP attributes, BGP communities may be acted upon
   or otherwise used by routing policies in other Autonomous Systems
   (ASes) on the Internet.






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   A BGP Communities attribute is a variable-length attribute consisting
   of a set of one or more four-octet values, each of which specify a
   community [RFC1997].  Common use of the individual values of this
   attribute type split this single 32-bit value into two 16-bit values.
   The most significant word is interpreted as an Autonomous System
   Number (ASN), and the least significant word is a locally defined
   value whose meaning is assigned by the operator of the AS in the most
   significant word.

   Since the adoption of four-octet ASNs [RFC6793], the BGP Communities
   attribute can no longer accommodate the above encoding, as a two-
   octet word cannot fit a four-octet ASN.  The BGP Extended Communities
   attribute [RFC4360] is also unsuitable.  The six-octet length of the
   Extended Community value precludes the common operational practice of
   encoding four-octet ASNs in both the Global Administrator and the
   Local Administrator sub-fields.

   To address these shortcomings, this document defines a BGP Large
   Communities attribute encoded as an unordered set of one or more
   twelve-octet values, each consisting of a four-octet Global
   Administrator field and two four-octet operator-defined fields, each
   of which can be used to denote properties or actions significant to
   the operator of the AS assigning the values.

2.  Requirements Language

   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].

3.  BGP Large Communities Attribute

   This document defines the BGP Large Communities attribute as an
   optional transitive path attribute of variable length.  All routes
   with the BGP Large Communities attribute belong to the communities
   specified in the attribute.















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   Each BGP Large Community value is encoded as a 12-octet quantity, as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Global Administrator                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Local Data Part 1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Local Data Part 2                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Global Administrator:  A four-octet namespace identifier.

   Local Data Part 1:  A four-octet operator-defined value.

   Local Data Part 2:  A four-octet operator-defined value.

   The Global Administrator field is intended to allow different ASes to
   define BGP Large Communities without collision.  This field SHOULD be
   an ASN, in which case the Local Data Parts are to be interpreted as
   defined by the owner of the ASN.  The use of Reserved ASNs (0
   [RFC7607], 65535 and 4294967295 [RFC7300]) is NOT RECOMMENDED.

   There is no significance to the order in which twelve-octet Large
   Community Attribute values are encoded in a Large Communities
   attribute, A BGP speaker can transmit them in any order.

   Duplicate BGP Large Community values MUST NOT be transmitted.  A
   receiving speaker MUST silently remove redundant BGP Large Community
   values from a BGP Large Community attribute.

4.  Aggregation

   If a range of routes is aggregated, then the resulting aggregate
   should have a BGP Large Communities attribute that contains all of
   the BGP Large Communities attributes from all of the aggregated
   routes.

5.  Canonical Representation

   The canonical representation of BGP Large Communities is three
   separate unsigned integers in decimal notation in the following
   order: Global Administrator, Local Data 1, Local Data 2.  Numbers
   MUST NOT contain leading zeros; a zero value MUST be represented with
   a single zero.  Each number is separated from the next by a single
   colon.  For example: 64496:4294967295:2, 64496:0:0.



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   BGP Large Communities SHOULD be represented in the canonical
   representation.

6.  Error Handling

   The error handling of BGP Large Communities is as follows:

   o  A BGP Large Communities attribute SHALL be considered malformed if
      the length of the BGP Large Communities Attribute value, expressed
      in octets, is not a non-zero multiple of 12.

   o  A BGP Large Communities attribute SHALL NOT be considered
      malformed due to presence of duplicate Large Community values.

   o  A BGP UPDATE message with a malformed BGP Large Communities
      attribute SHALL be handled using the approach of "treat-as-
      withdraw" as described in Section 2 of [RFC7606].

   The BGP Large Communities Global Administrator field may contain any
   value, and a BGP Large Communities attribute MUST NOT be considered
   malformed if the Global Administrator field contains an unallocated,
   unassigned, or reserved ASN.

7.  Security Considerations

   This document does not change any underlying security issues
   associated with any other BGP Communities mechanism.  Specifically,
   an AS relying on the BGP Large Communities attribute carried in BGP
   must have trust in every other AS in the path, as any intermediate AS
   in the path may have added, deleted, or altered the BGP Large
   Communities attribute.  Specifying the mechanism to provide such
   trust is beyond the scope of this document.

   BGP Large Communities do not protect the integrity of each community
   value.  Operators should be aware that it is possible for a BGP
   speaker to alter BGP Large Community Attribute values in a BGP Update
   Message.  Protecting the integrity of the transitive handling of BGP
   Large Community attributes in a manner consistent with the intent of
   expressed BGP routing policies falls within the broader scope of
   securing BGP, and is not specifically addressed here.

   Network administrators should note the recommendations in Section 11
   of "BGP Operations and Security" [RFC7454].








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8.  IANA Considerations

   IANA has assigned the value 32 (LARGE_COMMUNITY) in the "BGP Path
   Attributes" subregistry under the "Border Gateway Protocol (BGP)
   Parameters" registry.

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,
              <http://www.rfc-editor.org/info/rfc2119>.

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

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <http://www.rfc-editor.org/info/rfc7606>.

9.2.  Informative References

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

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

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <http://www.rfc-editor.org/info/rfc6793>.

   [RFC7300]  Haas, J. and J. Mitchell, "Reservation of Last Autonomous
              System (AS) Numbers", BCP 6, RFC 7300,
              DOI 10.17487/RFC7300, July 2014,
              <http://www.rfc-editor.org/info/rfc7300>.

   [RFC7454]  Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
              and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
              February 2015, <http://www.rfc-editor.org/info/rfc7454>.



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   [RFC7607]  Kumari, W., Bush, R., Schiller, H., and K. Patel,
              "Codification of AS 0 Processing", RFC 7607,
              DOI 10.17487/RFC7607, August 2015,
              <http://www.rfc-editor.org/info/rfc7607>.

Acknowledgments

   The authors would like to thank Ruediger Volk, Russ White, Acee
   Lindem, Shyam Sethuram, Jared Mauch, Joel M.  Halpern, Jeffrey Haas,
   Gunter van de Velde, Marco Marzetti, Eduardo Ascenco Reis, Mark
   Schouten, Paul Hoogsteder, Martijn Schmidt, Greg Hankins, Bertrand
   Duvivier, Barry O'Donovan, Grzegorz Janoszka, Linda Dunbar, Marco
   Davids, Gaurab Raj Upadhaya, Jeff Tantsura, Teun Vink, Adam
   Davenport, Theodore Baschak, Pier Carlo Chiodi, Nabeel Cocker, Ian
   Dickinson, Jan Baggen, Duncan Lockwood, David Farmer, Randy Bush, Wim
   Henderickx, Stefan Plug, Kay Rechthien, Rob Shakir, Warren Kumari,
   Gert Doering, Thomas King, Mikael Abrahamsson, Wesley Steehouwer,
   Sander Steffann, Brad Dreisbach, Martin Millnert, Christopher Morrow,
   Jay Borkenhagen, Arnold Nipper, Joe Provo, Niels Bakker, Bill Fenner,
   Tom Daly, Ben Maddison, Alexander Azimov, Brian Dickson, Peter van
   Dijk, Julian Seifert, Tom Petch, Tom Scholl, Arjen Zonneveld, Remco
   van Mook, Adam Chappell, Jussi Peltola, Kristian Larsson, Markus
   Hauschild, Richard Steenbergen, David Freedman, Richard Hartmann,
   Geoff Huston, Mach Chen, and Alvaro Retana for their support,
   insightful review, and comments.

Contributors

   The following people contributed significantly to the content of the
   document:

   John Heasley
   NTT Communications
   Email: heas@shrubbery.net

   Adam Simpson
   Nokia
   Email: adam.1.simpson@nokia.com













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Authors' Addresses

   Jakob Heitz (editor)
   Cisco
   170 West Tasman Drive
   San Jose, CA  95054
   United States of America

   Email: jheitz@cisco.com


   Job Snijders (editor)
   NTT Communications
   Theodorus Majofskistraat 100
   Amsterdam  1065 SZ
   The Netherlands

   Email: job@ntt.net


   Keyur Patel
   Arrcus, Inc.

   Email: keyur@arrcus.com


   Ignas Bagdonas
   Equinix
   80 Cheapside
   London  EC2V 6EE
   United Kingdom

   Email: ibagdona.ietf@gmail.com


   Nick Hilliard
   INEX
   4027 Kingswood Road
   Dublin  24
   Ireland

   Email: nick@inex.ie









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