4-Octet AS Specific BGP Extended Community
RFC 5668

Network Working Group                                         Y. Rekhter
Request for Comments: 5668                              Juniper Networks
Category: Standards Track                                      S. Sangli
                                                           Cisco Systems
                                                               D. Tappan
                                                              Consultant
                                                            October 2009

               4-Octet AS Specific BGP Extended Community

Abstract

   This document defines a new type of a BGP extended community, which
   carries a 4-octet Autonomous System (AS) number.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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 BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may

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RFC 5668         4-Octet AS Specific Extended Community     October 2009

   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

1.  Introduction

   This document defines a new type of BGP extended community [RFC4360]:
   a 4-octet AS specific extended community.  This type of extended
   community is similar to the 2-octet AS specific extended community,
   except that it can carry a 4-octet Autonomous System number.

1.1.  Specification of Requirements

   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.  4-Octet AS Specific Extended Community

   This is an extended type with a Type field comprising 2 octets and a
   Value field comprising 6 octets.

    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  |   Sub-Type    |    Global Administrator       :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   : Global Administrator (cont.)  |    Local Administrator        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   The Value field consists of 2 sub-fields:

      Global Administrator sub-field: 4 octets

         This sub-field contains a 4-octet Autonomous System number
         assigned by IANA.

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RFC 5668         4-Octet AS Specific Extended Community     October 2009

      Local Administrator sub-field: 2 octets

         The organization identified by the Autonomous System number in
         the Global Administrator sub-field can encode any information
         in this sub-field.  The format and meaning of the value encoded
         in this sub-field should be defined by the sub-type of the
         community.

3.  Considerations for 2-Octet Autonomous Systems

   As per [RFC4893], a 2-octet Autonomous System number can be converted
   into a 4-octet Autonomous System number by setting the 2 high-order
   octets of the 4-octet field to zero.

   As a consequence, at least in principle, an Autonomous System that
   uses a 2-octet Autonomous System number could use either 2-octet or
   4-octet AS specific extended communities.  This is undesirable, as
   both communities would be treated as different, even if they had the
   same Sub-Type and Local Administrator values.

   Therefore, for backward compatibility with existing deployments and
   to avoid inconsistencies between 2-octet and 4-octet specific
   extended communities, Autonomous Systems that use 2-octet Autonomous
   System numbers SHOULD use 2-octet AS specific extended communities
   rather than 4-octet AS specific extended communities.

4.  IANA Considerations

   This document defines a class of extended communities, called 4-octet
   AS specific extended communities, for which the IANA has created and
   will maintain a registry entitled Four-octet AS Specific Extended
   Community.  All the communities in this class are of extended Types.
   Future assignments are to be made using the "First Come First Served"
   policy defined in [RFC5226].  The Type values for the transitive
   communities of the 4-octet AS specific extended community class are
   0x0200-0x02ff; for the non-transitive communities of that class, they
   are 0x4200-0x42ff.  Assignments consist of a name and the value.

   This document makes the following assignments for the 4-octet AS
   specific extended community:

      Name                                     Type Value
      ----                                     ----------
      four-octet AS specific Route Target       0x0202
      four-octet AS specific Route Origin       0x0203

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RFC 5668         4-Octet AS Specific Extended Community     October 2009

5.  Security Considerations

   This document does not add new security issues.  All the security
   considerations for BGP extended communities apply here.  At the time
   that this document was written, there were significant efforts
   underway to improve the security properties of BGP.  For examples of
   documents that have been produced up to this time of publication, see
   [RFC4593] and [SIDR].

   There is a potential serious issue if a malformed, optional
   transitive attribute is received.  This issue and the steps to avoid
   it are discussed in [OPT_TRANS].

6.  Acknowledgements

   Thanks to Bruno Decraene for his contributions to this document.

7.  References

7.1.  Normative References

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

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

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

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

7.2.  Informative References

   [OPT_TRANS] Scudder, J., and E. Chen, "Error Handling for Optional
               Transitive BGP Attributes", Work in Progress, April 2009.

   [RFC4593]   Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
               Routing Protocols", RFC 4593, October 2006.

   [SIDR]      Lepinski, M. and S. Kent, "An Infrastructure to Support
               Secure Internet Routing", Work in Progress, July 2009.

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Authors' Addresses

   Yakov Rekhter
   Juniper Networks, Inc.
   EMail: yakov@juniper.net

   Srihari R. Sangli
   Cisco Systems, Inc.
   EMail: rsrihari@cisco.com

   Dan Tappan
   Boxborough MA
   EMail: Dan.Tappan@Gmail.com

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