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Network Working Group                                             D. Rao
Internet-Draft                                              P. Mohapatra
Intended status: Standards Track                           Cisco Systems
Expires: July 30, 2009                                           J. Haas
                                                          Arbor Networks
                                                        January 26, 2009


   Generic Subtype for BGP Four-octet AS specific extended community
         draft-ietf-idr-as4octet-extcomm-generic-subtype-00.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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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 extended community.  This document defines a
   new sub-type within the four-octet AS specific extended community to
   facilitate this practice.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   2.  Generic Sub-type Definition . . . . . . . . . . . . . . . . . . 3
   3.  Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6






























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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.
   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.

   [I-D.ietf-l3vpn-as4octet-ext-community] 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.

1.1.  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 RFC 2119 [RFC2119].


2.  Generic Sub-type Definition








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        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.


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 communities that encode AS_TRANS [RFC4893] as
   the first two octets.

   Similarly, a 2-octet AS number may have two valid representations as
   either a standard community or a 4-octet extended community with the
   upper two octets of the AS number set to zero.  For backward
   compatibility with existing deployments, and to avoid inconsistencies
   between standard communities and 4-octet extended communities, two-
   octet ASes SHOULD use standard 2-octet communities as defined in RFC
   1997 rather than the 4-octet AS specific community as defined in this
   document.



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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

   This document defines a specific application of the four-octet AS
   specific extended community.  IANA is requested to to assign a sub-
   type value of 0x04 for the generic four-octet AS specific extended
   community.

   This document makes the following assignments for the generic four-
   octet AS specific extended community:


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


6.  Security Considerations

   There are no additional security risks introduced by this design.


7.  Normative References

   [I-D.ietf-l3vpn-as4octet-ext-community]
              Rekhter, Y., Sangli, S., and D. Tappan, "Four-octet AS
              Specific BGP Extended Community",
              draft-ietf-l3vpn-as4octet-ext-community-02 (work in
              progress), November 2008.

   [RFC1997]  Chandrasekeran, R., Traina, P., and T. Li, "BGP
              Communities Attribute", RFC 1997, August 1996.

   [RFC1998]  Chen, E. and T. Bates, "An Application of the BGP
              Community Attribute in Multi-home Routing", RFC 1998,
              August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, February 2006.



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   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.


Authors' Addresses

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

   Email: dhrao@cisco.com


   Pradosh Mohapatra
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: pmohapat@cisco.com


   Jeffrey Haas
   Arbor Networks
   2727 S. State St.
   Ann Arbor, MI  48104
   USA

   Email: jhaas@arbor.net
















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