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Network Working Group                               Srihari R. Sangli
Internet Draft                                       Procket Networks
Expiration Date: September 2002
                                                        Daniel Tappan
                                                        Cisco Systems

                                                        Yakov Rekhter
                                                     Juniper Networks

                   BGP Extended Communities Attribute

               draft-ietf-idr-bgp-ext-communities-03.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.

   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.










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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 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 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:

         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 will determine if its a
         regular type or an extended type. The value of the high-order



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         octet of the Type Field defined as regular type (or extended
         type) for a extended community MUST NOT be reused as the value
         of the high-order octet of the Type Field defined as extended
         type (or regular type). In other words, a new extended
         community of regular type (extended type) should have unique
         (and new) value for the high-order octet (high-order and low-
         order octet).

         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

      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.














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5. New BGP Extended Community Types.

   This document introduces a 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 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 value and meaning of
               the value encoded in this sub-field should be defined by
               the sub-type 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 sub-types.

         The Value field consists of two sub-fields.

            Global Administrator sub-field: 4 octets

               This sub-field contains an IPv4 address assigned by IANA.

            Local Administrator sub-field: 2 octets

               The organization which has been assigned the IPv4 address
               in the Global Administrator sub-field, can encode any



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               information in this sub-field.  The value and meaning of
               this value encoded in this sub-field should be defined by
               the sub-type 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 sub-types.

         The Value Field consists of two sub-fields.

            Global Administrator sub-field: 4 octets

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

            Local Administrator sub-field: 2 octets

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

      Type 0x03:

         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
         0x03. The low-order octet of this extended type is used to
         indicate sub-types.

         The Value Field contains a 6 byte value of structure with sub-
         fields.

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








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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 can be
   0x00, 0x01 or 0x02. 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 or 0x02, the value of the
   Local Administrator sub-field in the Value Field MUST be unique
   within the Autonomous system carried in the Global Administrator sub-
   field.


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 can be
   0x00, 0x01 or 0x02. 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 or 0x02, the value of the
   Local Administrator sub-field in the Value Field MUST be unique
   within the Autonomous system carried in the Global Administrator sub-
   field.


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
   MAY be marked as non-transitive across the Autonomous system
   boundary.

   If the community is marked as non-transitive, then the value of the
   high-order octet of the extended Type Field is 0x40, otherwise it is
   0x00.  The value of the low-order octet of the extended type field
   for this community is 0x04.




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   The value of the Global Administrator sub-field 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 sub-field to see 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 sub-field 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 a 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

   For the high-order octet of the Type Field, values 0x00 through 0x03
   are assigned in this document and are defined as extended types. For
   the combination of the high-order and low-order octets of the Type
   Field values 0x0002-0x0004, 0x0102-0x0103, and 0x0202-0x0203 are
   assigned in this document.

   The Type Field values 0x04-0x3f for regular types (0x0400-0x3fff when
   expressed as extended types) are to be assigned by IANA, using the
   "First Come First Served" policy defined in RFC 2434. The extended
   type field values 0x0000-0x0001, 0x0005-0x00ff, 0x0100-0x0101,
   0x0104-0x01ff, 0x0200-0x0201, 0x0204-0x02ff and 0x0300-0x03ff are to



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   be assigned by IANA, using the "First Come First Served" policy
   defined in RFC 2434. Type values 0x80-0xbf for regular types
   (0x8000-0xbfff when expressed as extended types) are 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, Bruno
   Rijsman for their suggestions and 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 R. Sangli
   Procket Networks, Inc.
   1100 Cadillac Court
   Milpitas, CA - 95035
   e-mail: srihari@procket.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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