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Network Working Group                                             D. Rao
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                            P. Mohapatra
Expires: June 4, 2017                                   Sproute Networks
                                                                 J. Haas
                                                  Juniper Networks, Inc.
                                                        December 1, 2016


   Generic Subtype for BGP Four-octet AS specific extended community
           draft-ietf-idr-as4octet-extcomm-generic-subtype-10

Abstract

   Maintaining the current best practices with communities, ISPs and
   enterprises that are assigned a 4-octet AS number may want the BGP
   UPDATE messages they receive from their customers or peers to include
   a 4-octet AS specific BGP extended community.  This document defines
   a new sub-type within the four-octet AS specific extended community
   to facilitate this practice.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
   be interpreted as described in [RFC2119] only when they appear in all
   upper case.  They may also appear in lower or mixed case as English
   words, without normative meaning.

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 http://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 June 4, 2017.






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Copyright Notice

   Copyright (c) 2016 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.  Generic Sub-type Definition . . . . . . . . . . . . . . . . .   3
   3.  Deployment Considerations . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Maintaining the current best practices with communities, ISPs and
   enterprises that are assigned a 4-octet AS number may want the BGP
   UPDATE messages they receive from their customers or peers to include
   a 4-octet AS specific extended community.  This document defines a
   new sub-type within the four-octet AS specific extended community to
   facilitate this practice.

   For example, [RFC1998] describes an application of BGP community
   attribute ([RFC1997]) to implement flexible routing policies for
   sites multi-homed to one or multiple providers.  In a two-octet AS
   environment, the advertised routes are usually associated with a
   community attribute that encodes the provider's AS number in the
   first two octets of the community and a LOCAL_PREF value in the
   second two octets of the community.  The community attribute signals
   the provider edge routers connected to the site to set the
   corresponding LOCAL_PREF on their advertisements to the IBGP mesh.




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   In this way, customers can put into practice topologies like active-
   backup.

   When such a provider is assigned a four-octet AS number, the existing
   mechanism of using communities is not sufficient since the AS portion
   of the RFC 1997 community cannot exceed two bytes.  The natural
   alternative is to extend the same mechanism using extended
   communities since it allows for encoding eight bytes of information.

   [RFC5668] defines a format for a four-octet AS specific extended
   community with a designated type field.  That document defines two
   sub-types: Four-octet specific Route Target extended community and
   Four-octet specific Route Origin extended community.  This document
   specifies a generic sub-type for the four-octet AS specific extended
   community to provide benefits such as the one cited above as the
   Internet migrates to four-octet AS space.

2.  Generic Sub-type Definition

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | 0x02 or 0x42  |     0x04      |           Global              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Administrator              |    Local Administrator        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This is an extended type with Type Field comprising of 2 octets and
   Value Field comprising of 6 octets.

   The high-order octet of this extended type is set to either 0x02 (for
   transitive communities) or 0x42 (for non-transitive communities).
   The low-order octet or the sub-type is set to 0x04.

   The Value Field consists of two sub-fields:



      Global Administrator sub-field: 4 octets

          This sub-field contains a four-octet Autonomous System number.

      Local Administrator sub-field: 2 octets

          This sub-field contains a value that can influence routing
          policies.  This value has semantics that are of significance
          for the Autonomous System in the Global Administrator field.




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3.  Deployment Considerations

   There are situations in peering where a 4-octet AS specific generic
   extended community cannot be used.

   A speaker with a 4-octet AS may not support 4-octet extended
   communities; or the speaker may have a customer or peer that does not
   support 4-octet extended communities.  In all such cases, the speaker
   may need to define an appropriate standard community value for the
   same purpose.  As an example, a peer may tag its routes with a
   community that encodes AS_TRANS [RFC4893] as the first two octets.

   Similarly, as per [RFC4893], a 2-octet Autonomous System number can
   be converted into a 4-octet Autonomous System number by setting the
   two high-order octets of the 4-octet field to zero.  As a
   consequence, at least in principle, an Autonomous System that has a
   2-octet AS number could use either a standard community or the
   4-octet AS specific generic extended community.  This is undesirable,
   as they would be treated as different communities, even if they had
   the same values.

   Therefore, for backward compatibility with existing deployments and
   to avoid inconsistencies between standard communities and 4-octet
   extended communities, Autonomous Systems that use 2-octet Autonomous
   System numbers SHOULD use standard 2-octet communities as defined in
   RFC1997 rather than the 4-octet AS specific extended community as
   defined in this document.

4.  Acknowledgments

   The authors would like to thank Paul Jakma, Bruno Decraene and Cayle
   Spandon for their useful comments on the document.

5.  IANA Considerations

   Prior revisions of this document requested IANA to make assignments
   from the Transitive Four-Octet AS Specific Extended Community Sub-
   Type registry and the Non-Transitive Four-Octet AS Specific Extended
   Community Sub-Type registry.  The sub-type value of 0x04 in each of
   those registries was previously assigned:

      Name                                           Value
      ----                                           -----
      transitive generic four-octet AS specific      0x0204
      non-transitive generic four-octet AS specific  0x4204

   IANA is requested to deprecate these assignments.




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6.  Security Considerations

   There are no additional security risks introduced by this design.

7.  References

7.1.  Normative 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>.

   [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>.

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

   [RFC5668]  Rekhter, Y., Sangli, S., and D. Tappan, "4-Octet AS
              Specific BGP Extended Community", RFC 5668,
              DOI 10.17487/RFC5668, October 2009,
              <http://www.rfc-editor.org/info/rfc5668>.

7.2.  Informative References

   [I-D.ietf-idr-large-community]
              Heitz, J., Snijders, J., Patel, K., Bagdonas, I., and N.
              Hilliard, "BGP Large Communities", draft-ietf-idr-large-
              community-09 (work in progress), November 2016.

   [RFC1998]  Chen, E. and T. Bates, "An Application of the BGP
              Community Attribute in Multi-home Routing", RFC 1998,
              DOI 10.17487/RFC1998, August 1996,
              <http://www.rfc-editor.org/info/rfc1998>.

Appendix A.  Document History

   This final version of the document exists only to request IANA to
   deprecate its prior Extended Community assignments and provide a
   historical record of the reason.

   During the development of the BGP Four-octet feature [RFC4893],
   operators had offered their commentarythat parity was needed with
   existing BGP Community practices similar to those defined in
   [RFC1998].  What became clear over time was that some operators



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   encoded an AS number as the second field of their community;
   essentially, as the "target".

   Since an Extended Community's Local Administrator field cannot encode
   more than two octets of value, the Extended Community format was not
   appropriate for addressing parity of existing operational practices.
   The BGP Large Communities Feature [I-D.ietf-idr-large-community]
   supplanted the work begun in this document.

Authors' Addresses

   Dhananjaya Rao
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: dhrao@cisco.com


   Pradosh Mohapatra
   Sproute Networks

   Email: mpradosh@yahoo.com


   Jeffrey Haas
   Juniper Networks, Inc.
   1133 Innovation Way
   Sunnyvale, CA  94089
   US

   Email: jhaas@juniper.net


















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