path: root/doc/rfc/rfc4360.txt

Network Working Group                                          S. Sangli
Request for Comments: 4360                                     D. Tappan
Category: Standards Track                                  Cisco Systems
                                                              Y. Rekhter
                                                        Juniper Networks
                                                           February 2006


                   BGP Extended Communities Attribute

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) The Internet Society (2006).

Abstract

   This document describes the "extended community" BGP-4 attribute.
   This attribute provides a mechanism for labeling information carried
   in BGP-4.  These labels can be used to control the distribution of
   this information, or for other applications.

1.  Introduction

   The Extended Community Attribute provides a mechanism for labeling
   information carried in BGP-4 [BGP-4].  It provides two important
   enhancements over the existing BGP Community Attribute [RFC1997]:

      - An extended range, ensuring that communities can be assigned for
        a plethora of uses, without fear of overlap.

      - The addition of a Type field provides structure for the
        community space.

   The addition of structure allows the usage of policy based on the
   application for which the community value will be used.  For example,
   one can filter out all communities of a particular type, or allow
   only certain values for a particular type of community.  It also
   allows one to specify whether a particular community is transitive or
   non-transitive across an Autonomous System (AS) boundary.  Without
   structure, this can only be accomplished by explicitly enumerating



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   all community values that will be denied or allowed and passed to BGP
   speakers in neighboring ASes based on the transitive property.

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.  BGP Extended Communities Attribute

   The Extended Communities Attribute is a transitive optional BGP
   attribute, with the Type Code 16.  The attribute consists of a set of
   "extended communities".  All routes with the Extended Communities
   attribute belong to the communities listed in the attribute.

   Each Extended Community is encoded as an 8-octet quantity, as
   follows:

      - Type Field  : 1 or 2 octets
      - Value Field : Remaining 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type high    |  Type low(*)  |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          Value                |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      (*) Present for Extended types only, used for the Value field
          otherwise.

      Type Field:

         Two classes of Type Field are introduced: Regular type and
         Extended type.

         The size of Type Field for Regular types is 1 octet, and the
         size of the Type Field for Extended types is 2 octets.

         The value of the high-order octet of the Type Field determines
         if an extended community is a Regular type or an Extended type.
         The class of a type (Regular or Extended) is not encoded in the
         structure of the type itself.  The class of a type is specified
         in the document that defines the type and the IANA registry.





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         The high-order octet of the Type Field is as shown below:

             0 1 2 3 4 5 6 7
            +-+-+-+-+-+-+-+-+
            |I|T|           |
            +-+-+-+-+-+-+-+-+

            I - IANA authority bit

               Value 0: IANA-assignable type using the "First Come First
               Serve" policy

               Value 1: Part of this Type Field space is for IANA
               assignable types using either the Standard Action or the
               Early IANA Allocation policy.  The rest of this Type
               Field space is for Experimental use.

            T - Transitive bit

               Value 0: The community is transitive across ASes

               Value 1: The community is non-transitive across ASes

            Remaining 6 bits: Indicates the structure of the community

      Value Field:

         The encoding of the Value Field is dependent on the "type" of
         the community as specified by the Type Field.

   Two extended communities are declared equal only when all 8 octets of
   the community are equal.

   The two members in the tuple <Type, Value> should be enumerated to
   specify any community value.  The remaining octets of the community
   interpreted based on the value of the Type field.

3.  Defined BGP Extended Community Types

   This section introduces a few extended types and defines the format
   of the Value Field for those types.  The types introduced here
   provide "templates", where each template is identified by the high-
   order octet of the extended community Type field, and the lower-order
   octet (sub-type) is used to indicate a particular type of extended
   community.






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3.1.  Two-Octet AS Specific Extended Community

   This is an extended type with Type Field composed of 2 octets and
   Value Field composed of 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x00 or 0x40  |   Sub-Type    |    Global Administrator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Administrator                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value of the high-order octet of this extended type is either
   0x00 or 0x40.  The low-order octet of this extended type is used to
   indicate sub-types.

   The Value Field consists of two sub-fields:

      Global Administrator sub-field: 2 octets

         This sub-field contains an Autonomous System number assigned by
         IANA.

      Local Administrator sub-field: 4 octets

         The organization identified by 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.

3.2.  IPv4 Address Specific Extended Community

   This is an extended type with Type Field composed of 2 octets and
   Value Field composed of 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x01 or 0x41  |   Sub-Type    |    Global Administrator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Global Administrator (cont.)  |    Local Administrator        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value of the high-order octet of this extended type is either
   0x01 or 0x41.  The low-order octet of this extended type is used to
   indicate sub-types.



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   The Value field consists of two sub-fields:

      Global Administrator sub-field: 4 octets

         This sub-field contains an IPv4 unicast address assigned by one
         of the Internet registries.

      Local Administrator sub-field: 2 octets

         The organization that has been assigned the IPv4 address in the
         Global Administrator sub-field can encode any information in
         this sub-field.  The format and meaning of this value encoded
         in this sub-field should be defined by the sub-type of the
         community.

3.3.  Opaque Extended Community

   This is an extended type with Type Field composed of 2 octets and
   Value Field composed of 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x03 or 0x43  |   Sub-Type    |                Value          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Value (cont.)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value of the high-order octet of this extended type is either
   0x03 or 0x43.  The low-order octet of this extended type is used to
   indicate sub-types.

   This is a generic community of extended type.  The value of the sub-
   type that should define the Value Field is to be assigned by IANA.

4.  Route Target Community

   The Route Target Community identifies one or more routers that may
   receive a set of routes (that carry this Community) carried by BGP.
   This is transitive across the Autonomous System boundary.

   The Route Target Community is of an extended type.

   The value of the high-order octet of the Type field for the Route
   Target Community can be 0x00, 0x01, or 0x02.  The value of the low-
   order octet of the Type field for this community is 0x02.





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   When the value of the high-order octet of the Type field is 0x00 or
   0x02, the Local Administrator sub-field contains a number from a
   numbering space that is administered by the organization to which the
   Autonomous System number carried in the Global Administrator sub-
   field has been assigned by an appropriate authority.

   When the value of the high-order octet of the Type field is 0x01, the
   Local Administrator sub-field contains a number from a numbering
   space that is administered by the organization to which the IP
   address carried in the Global Administrator sub-field has been
   assigned by an appropriate authority.

   One possible use of the Route Target Community is specified in
   [RFC4364].

5.  Route Origin Community

   The Route Origin Community identifies one or more routers that inject
   a set of routes (that carry this Community) into BGP.  This is
   transitive across the Autonomous System boundary.

   The Route Origin Community is of an extended type.

   The value of the high-order octet of the Type field for the Route
   Origin Community can be 0x00, 0x01, or 0x02.  The value of the low-
   order octet of the Type field for this community is 0x03.

   When the value of the high-order octet of the Type field is 0x00 or
   0x02, the Local Administrator sub-field contains a number from a
   numbering space that is administered by the organization to which the
   Autonomous System number carried in the Global Administrator sub-
   field has been assigned by an appropriate authority.

   When the value of the high-order octet of the Type field is 0x01, the
   Local Administrator sub-field contains a number from a numbering
   space that is administered by the organization to which the IP
   address carried in the Global Administrator sub-field has been
   assigned by an appropriate authority.

   One possible use of the Route Origin Community is specified in
   [RFC4364].










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6.  Operations

   A BGP speaker may use the Extended Communities attribute to control
   which routing information it accepts or distributes to its peers.

   The Extended Community attribute MUST NOT be used to modify the BGP
   best path selection algorithm in a way that leads to forwarding
   loops.

   A BGP speaker receiving a route that doesn't have the Extended
   Communities attribute MAY append this attribute to the route when
   propagating it to its peers.

   A BGP speaker receiving a route with the Extended Communities
   attribute MAY modify this attribute according to the local policy.

   By default if a range of routes is to be aggregated and the resultant
   aggregates path attributes do not carry the ATOMIC_AGGREGATE
   attribute, then the resulting aggregate should have an Extended
   Communities path attribute that contains the set union of all the
   Extended Communities from all of the aggregated routes.  The default
   behavior could be overridden via local configuration, in which case
   handling the Extended Communities attribute in the presence of route
   aggregation becomes a matter of the local policy of the BGP speaker
   that performs the aggregation.

   If a route has a non-transitivity extended community, then before
   advertising the route across the Autonomous System boundary the
   community SHOULD be removed from the route.  However, the community
   SHOULD NOT be removed when advertising the route across the BGP
   Confederation boundary.

   A route may carry both the BGP Communities attribute, as defined in
   [RFC1997]), and the Extended BGP Communities attribute.  In this
   case, the BGP Communities attribute is handled as specified in
   [RFC1997], and the Extended BGP Communities attribute is handled as
   specified in this document.

7.  IANA Considerations

   All the BGP Extended Communities contain a Type field.  The IANA has
   created a registry entitled, "BGP Extended Communities Type".  The
   IANA will maintain this registry.

   The Type could be either regular or extended.  For a regular Type the
   IANA allocates an 8-bit value; for an extended Type the IANA
   allocates a 16-bit value.




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   The value allocated for a regular Type MUST NOT be reused as the
   value of the high-order octet when allocating an extended Type.  The
   value of the high-order octet allocated for an extended Type MUST NOT
   be reused when allocating a regular Type.

   The Type field indicates where the Extended Community is transitive
   or not.  Future requests for assignment of a Type value must specify
   whether the Type value is intended for a transitive or a non-
   transitive Extended Community.

   Future assignment are to be made using either the Standards Action
   process defined in [RFC2434], the Early IANA Allocation process
   defined in [RFC4020], or the "First Come First Served" policy defined
   in [RFC2434].

   The following table summarizes the ranges for the assignment of
   Types:

      Type                        Standard Action         First Come
                                  Early IANA Allocation   First Served
      ------------------          ---------------------   ------------

      regular, transitive          0x90-0xbf              0x00-x3f

      regular, non-transitive      0xd0-0xff              0x40-0x7f

      extended, transitive         0x9000-0xbfff          0x0000-0x3fff

      extended, non-transitive     0xd000-0xffff          0x4000-0x7fff

   Assignments consist of a name and the value.

   The Type values 0x80-0x8f and 0xc0-0xcf for regular Types, and
   0x8000-0x8fff and 0xc000-0xcfff for extended Types are for
   Experimental use as defined in RFC 3692.

   This document defines a class of extended communities called two-
   octet AS specific extended community for which the IANA is to create
   and maintain a registry entitled "Two-octet AS Specific Extended
   Community".  All the communities in this class are of extended Types.
   Future assignment are to be made using the "First Come First Served"
   policy defined in [RFC2434].  The Type values for the transitive
   communities of the two-octet AS specific extended community class are
   0x0000-0x00ff, and for the non-transitive communities of that class
   are 0x4000-0x40ff.  Assignments consist of a name and the value.

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



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      Name                                     Type Value
      ----                                     ----------
      two-octet AS specific Route Target       0x0002
      two-octet AS specific Route Origin       0x0003

   This document defines a class of extended communities called IPv4
   address specific extended community for which the IANA is to create
   and maintain a registry entitled "IPv4 Address Specific Extended
   Community".  All the communities in this class are of extended Types.
   Future assignment are to be made using the "First Come First Served"
   policy defined in [RFC2434].  The Type values for the transitive
   communities of the two-octet AS specific extended community class
   are 0x0100-0x01ff, and for the non-transitive communities of that
   class are 0x4100-0x41ff.  Assignments consist of a name and the
   value.

   This document makes the following assignments for the IPv4 address
   specific extended community:

      Name                                     Type Value
      ----                                     ----------
      IPv4 address specific Route Target       0x0102
      IPv4 address specific Route Origin       0x0103

   This document defines a class of extended communities called opaque
   extended community for which the IANA is to create and maintain a
   registry entitled "Opaque Extended Community".  All the communities
   in this class are of extended Types.  Future assignment are to be
   made using the "First Come First Served" policy defined in [RFC2434].
   The Type values for the transitive communities of the opaque extended
   community class are 0x0300-0x03ff, and for the non-transitive
   communities of that class are 0x4300-0x43ff.  Assignments consist of
   a name and the value.

   When requesting an allocation from more than one registry defined
   above, one may ask for allocating the same Type value from these
   registries.  If possible, the IANA should accommodate such requests.

8.  Security Considerations

   This extension to BGP has similar security implications as BGP
   Communities [RFC1997].

   This extension to BGP does not change the underlying security issues.
   Specifically, an operator who is relying on the information carried
   in BGP must have a transitive trust relationship back to the source
   of the information.  Specifying the mechanism(s) to provide such a
   relationship is beyond the scope of this document.



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9.  Acknowledgements

   The authors would like to thank John Hawkinson, Jeffrey Haas, Bruno
   Rijsman, Bill Fenner, and Alex Zinin for their suggestions and
   feedback.

10.  Normative References

   [BGP-4]        Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
                  (BGP-4)", RFC 4271, January 2006.

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

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

   [RFC2434]      Narten, T. and H. Alvestrand, "Guidelines for Writing
                  an IANA Considerations Section in RFCs", BCP 26, RFC
                  2434, October 1998.

   [RFC4020]      Kompella, K. and A. Zinin, "Early IANA Allocation of
                  Standards Track Code Points", BCP 100, RFC 4020,
                  February 2005.

11.  Informative References

   [RFC4364]      Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
                  Networks (VPNs)", RFC 4364, February 2006.






















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Authors' Addresses

   Srihari R. Sangli
   Cisco Systems, Inc.

   EMail: rsrihari@cisco.com


   Dan Tappan
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA 01824

   EMail: tappan@cisco.com


   Yakov Rekhter
   Juniper Networks, Inc.
   1194 N. Mathilda Ave
   Sunnyvale, CA 94089

   EMail: yakov@juniper.net





























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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

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Acknowledgement

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   Administrative Support Activity (IASA).







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