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
  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 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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     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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RFC 5668         4-Octet AS Specific Extended Community     October 2009


Authors' Addresses

  Yakov Rekhter
  Juniper Networks, Inc.
  EMail: [email protected]


  Srihari R. Sangli
  Cisco Systems, Inc.
  EMail: [email protected]


  Dan Tappan
  Boxborough MA
  EMail: [email protected]




































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