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Network Working Group                           Srihari Ramachandra
Internet Draft                                        Daniel Tappan
Expiration Date: June 2001                            cisco Systems

                   BGP Extended Communities Attribute

              draft-ramachandra-bgp-ext-communities-07.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.

   Internet-Drafts are draft documents valid for a maximum of six months
   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. Without
   structure this can only be accomplished by explicitly enumerating all
   community values which will be denied or allowed.




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: 2 octets

         Types 0 through 0x7fff inclusive are assignable by IANA.  Types
         0x8000 through 0xffff inclusive are vendor-specific.

      - Value Field: 6 octets

         When the high-order octet of the Type field is 0x00, the Value
         field consists of two subfields:

            Administrator: 2 octets

               This subfield contains an Autonomous System number
               assigned by IANA.

            Assigned Number subfield: 4 octets

               This subfield contains a number from a numbering space
               which is administered by the organization to which the
               Automous System number in the Administrator subfield has
               been assigned by IANA.

         When the high-order octet of the Type field is 0x01, the Value
         field consists of two subfields:

            Administrator: 4 octets

               This subfield contains an IPv4 address assigned by IANA.

            Assigned Number subfield: 2 octets

               This subfield contains a number from a numbering space
               which is administered by the organization to which the
               IPv4 address in the Administrator subfield has been
               assigned by IANA.

         When the high-order octet of the Type field is 0x10, the Value
         field consists of two subfields:

            Administrator: 4 octets

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

            Assigned Number subfield: 2 octets

               This subfield contains a number from a numbering space
               which is administered by the organization to which the
               Automous System number in the Administrator subfield has
               been assigned by IANA.


5. 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.

   The Type field for the Route Target Community is 0x0002 or 0x0102.


6. Route Origin Community

   The Route Origin Community identifies one or more routers that inject
   a set of routes (that carry this Community) into BGP.

   The Type field for the Route Origin Community is 0x0003 or 0x0103.


7. Link Bandwidth Community

   When a router receives a route from a directly connected external
   neigbor (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. This bandwidth
   is carried in the Link Bandwidth Community, and is encoded as 4
   octets in IEEE floating point format. The units are bytes per second.

   A router is expected to strip the Link Bandwidth Community attribute
   from a route when advertising this route to an external neighbor.

   When a router receives a route with the Link Bandwidth Community, the
   router should ignore the information carried in the Link Bandwidth
   Community of the route if this Community was attached to the route by
   some router that is in a different Autonomous System than the router
   that receives the route. The router that receives the route
   determines the Autonomous System of the router that attached the Link
   Bandwidth Community by examining the Community itself (as it carried
   the Autonomous System of the router that attached the Community).

   The Type field for the Link Bandwidth Community is 0x0004.



8. 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 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.


9. IANA Considerations

   As specified in section 4  of this document, an Extended Community
   Attribute contains a  two-byte Type Field. Type Field  values 2, 3,
   and 4  are assigned in this document.  Type  Field values 5-0x7fff
   are  to be assigned by IANA, using the "First  Come First Served"
   policy defined in RFC 2434.  Type values  0x8000-0xffff are for
   vendor-specific  types, and values in this range are not to be
   assigned by IANA.


10. Security Considerations

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


11. Acknowledgements

   To be supplied.


12. 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.


13. 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


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