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Network Working Group                             Srihari Ramachandra
Internet Draft                                          Daniel Tappan
Expiration Date: December 2001                          Cisco Systems

                                                        Yakov Rekhter
                                                     Juniper Networks

                   BGP Extended Communities Attribute

              draft-ramachandra-bgp-ext-communities-09.txt


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
   produce derivative works is not granted.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

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   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


2. Abstract

   This document describes an extension to BGP [BGP-4] which may be used
   to provide flexible control over the distribution of routing
   information.


3. Introduction

   The Extended Community Attribute provides two important enhancements
   over the existing BGP Community Attribute:

      - It provides 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 application 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 Autonomous system boundary. Without structure
   this can only be accomplished by explicitly enumerating all community
   values which will be denied or allowed and passed to BGP speakers in
   neighboring ASes based on the transitive property.


4. BGP Extended Communities Attribute

   The Extended Communities Attribute is a transitive optional BGP
   attribute.  The attribute consists of a set of "extended
   communities".  Each extended community is coded as an eight octet
   value.  All routes with  the Extended Communities attribute belong to
   the communities listed in the attribute.

   The Extended Communities Attribute has Type Code 16.

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

      - Type Field  : 1 or 2 octets
      - Value Field : Remaining octets

      Type Field:

         The value of the high-order octet will determine if its a
         regular type or 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 high-order octet of the Type Field is as shown below:

            First bit (MSB)   : IANA authority bit
                                Value 0 : IANA assignable type
                                Value 1 : Vendor-specific types

            Second bit        : 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

         For regular types, values of the Type Field 0 through 0x3f
         inclusive are assignable by IANA. The values 0x80 through 0xbf
         inclusive are vendor-specific.

         For extended types, values of the Type Field 0 through 0x3fff
         inclusive are assignable by IANA. The values 0x8000 through
         0xbfff inclusive are vendor-specific.

      Value Field:

         The encoding of the Value Field is dependent on the "type" of
         the community as specified by the Type Field. The encoding of
         the community for the transitive communities should be such
         that it is unique globally (i.e.  across the Autonomous
         Systems).

      Two extended communities are declared equal only when entire 8
      octets are equal.

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


5. New BGP Extended Community Types.

   This document introduces few extended types and defines the Value
   Field for those types.

      Type 0x00:

         This is an extended type with Type Field comprising of 2 octets
         and Value Field comprising of 6 octets.

         The value of the high-order octet of this extended type is
         0x00. The low-order octet of this extended type is used to
         indicate subtypes.

         The Value Field consists of two subfields:

            Global Administrator subfield: 2 octets

               This subfield contains an Autonomous System number
               assigned by IANA.

            Local Administrator subfield: 4 octets

               The organization identified by Autonomous System number
               in the Global Administrator subfield, can encode any
               information in this subfield.  The value and meaning of
               the value encoded in this subfield should be defined by
               the subtype of the community.

      Type 0x01:

         This is an extended type with Type Field comprising of 2 octets
         and Value Field comprising of 6 octets.

         The value of the high-order octet of this extended type is
         0x01. The low-order octet of this extended type is used to
         indicate subtypes.

         The Value field consists of two subfields.

            Global Administrator subfield: 4 octets

               This subfield contains an IPv4 address assigned by IANA.

            Local Administrator subfield: 2 octets

               The organization which has been assigned the IPv4 address
               in the Global Administrator subfield, can encode any
               information in this subfield.  The value and meaning of
               this value encoded in this subfield should be defined by
               the subtype of the community.

      Type 0x02:

         This is an extended type with Type Field comprising of 2 octets
         and Value Field comprising of 6 octets.

         The value of the high-order octet of this extended type is
         0x02. The low-order octet of this extended type is used to
         indicate subtypes.

         The Value Field consists of two subfields.

            Global Administrator subfield: 4 octets

               This subfield contains a 4-octets Autonomous System
               number assigned by IANA.

            Local Administrator subfield: 2 octets

               The organization identified by Autonomous System number
               in the Global Administrator subfield, can encode any
               information in this subfield.  The value and meaning of
               the value encoded in this subfield should be defined by
               the subtype of the community.


6. 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 value of the Type field for the Route Target Community is 0x00 or
   0x01.  The value of the low-order octet of the extended type field
   for this community is 0x02.

   When the value of the Type field is 0x00, the value of the Local
   Administrator subfield in the Value Field MUST be unique within the
   Autonomous system carried in the Global Administrator subfield.


7. 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 value of the Type field for the Route Origin Community is 0x00 or
   0x01.  The value of the low-order octet of the extended type field
   for this community is 0x03.

   When the value of the Type field is 0x00, the value of the Local
   Administrator subfield in the Value Field MUST be unique within the
   Autonomous system carried in the Global Administrator subfield.









8. Link Bandwidth Community

   When a router receives a route from a directly connected external
   neighbor (the external neighbor that is one IP hop away), and
   advertises this route (via IBGP) to internal neighbors, as part of
   this advertisement the router may carry the bandwidth of the link
   that connects the router with the external neighbor. The bandwidth of
   such a link is carried in the Link Bandwidth Community. The community
   is non-transitive across the Autonomous system boundary.

   The value of the high-order octet of the extended Type Field is 0x40.
   The value of the low-order octet of the extended type field for this
   community is 0x04.

   The value of the Global Administrator subfield in the Value Field
   MUST represent the Autonomous System of the router that attaches the
   Link Bandwidth Community. When a router receives a route with the
   community, the router may check the AS number in the Global
   Administrator subfield to see if its if its not the local AS and
   hence ignore the information carried in the Link Bandwidth Community.

   The bandwidth of the link is expressed as 4 octets in IEEE floating
   point format, units being bytes per second. It is carried in the
   Local Administrator subfield of the Value Field.


9. Operations

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

   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.

   A BGP speaker should not propagate the non-transitive extended
   community across the Autonomous system 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.













10. IANA Considerations

   The Type Field  values 0x00 and 0x01 are assigned in this document.
   Type  Field values 2-0x3fff for extended-types (2-0x3f for regular
   types) are  to be assigned by IANA, using the "First  Come First
   Served" policy defined in RFC 2434. Type values 0x8000-0xbfff for
   extended-types (0x80-0xbf for regular-types) are for vendor-specific
   types, and values in this range are not to be assigned by IANA.


11. Security Considerations

   This extension to BGP does not change the underlying security issues.


12. Acknowledgements

   The authors would like to thank John Hawkinson, Jeffrey Haas for
   their feedback.


13. References

   [BGP-4]   Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-
   4)", RFC 1771, March 1995.

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


14. Author Information


   Srihari Ramachandra
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   e-mail: rsrihari@cisco.com

   Dan Tappan
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA 01824
   e-mail: tappan@cisco.com

   Yakov Rekhter
   Juniper Networks, Inc.
   1194 N. Mathilda Ave
   Sunnyvale, CA 94089
   e-mail: yakov@juniper.net


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