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rfc:rfc4360

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]:
  1. An extended range, ensuring that communities can be assigned for

a plethora of uses, without fear of overlap.

  1. 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

Sangli, et al. Standards Track [Page 1] RFC 4360 BGP Extended Communities Attribute February 2006

 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:
  1. Type Field : 1 or 2 octets
  2. 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.

Sangli, et al. Standards Track [Page 2] RFC 4360 BGP Extended Communities Attribute February 2006

       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.

Sangli, et al. Standards Track [Page 3] RFC 4360 BGP Extended Communities Attribute February 2006

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.

Sangli, et al. Standards Track [Page 4] RFC 4360 BGP Extended Communities Attribute February 2006

 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.

Sangli, et al. Standards Track [Page 5] RFC 4360 BGP Extended Communities Attribute February 2006

 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].

Sangli, et al. Standards Track [Page 6] RFC 4360 BGP Extended Communities Attribute February 2006

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.

Sangli, et al. Standards Track [Page 7] RFC 4360 BGP Extended Communities Attribute February 2006

 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:

Sangli, et al. Standards Track [Page 8] RFC 4360 BGP Extended Communities Attribute February 2006

    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.

Sangli, et al. Standards Track [Page 9] RFC 4360 BGP Extended Communities Attribute February 2006

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.

Sangli, et al. Standards Track [Page 10] RFC 4360 BGP Extended Communities Attribute February 2006

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

Sangli, et al. Standards Track [Page 11] RFC 4360 BGP Extended Communities Attribute February 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
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 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 Administrative Support Activity (IASA).

Sangli, et al. Standards Track [Page 12]

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