Network Working Group               Srihari R. Sangli (Procket Networks)
Internet Draft                                       Procket Networks                             Daniel Tappan (Cisco Systems)
Expiration Date: September October 2002
                                                        Daniel Tappan
                                                        Cisco Systems           Yakov Rekhter
                                                     Juniper Networks (Juniper Networks)

                   BGP Extended Communities Attribute

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

               draft-ietf-idr-bgp-ext-communities-04.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] BGP-4 which may be used to
   provide flexible control over the distribution of routing
   information.

3. 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].

4. 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.

5. BGP Extended Communities Attribute

   The Extended Communities Attribute is a transitive optional BGP
   attribute.
   attribute, with the Type Code 16.  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

        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 will determine if its a
         regular type or an extended type. The value of the high-order
         octet of the Type Field defined as regular type (or extended
         type) for a determines
         if an 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, is a new extended
         community of regular Regular type (extended type) should have unique
         (and new) value for the high-order octet (high-order and low-
         order octet). or an Extended type.

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

            First bit (MSB)   :

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

            I - IANA authority bit

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

               Value 1 : Vendor-specific types

            Second bit        : 1: IANA assignable type using the IETF Consensus
               policy and experimental

            T - Transitive bit

               Value 0 : 0: The community is
                                          Transitive transitive across ASes

               Value 1 : 1: The community is
                                          Non-Transitive non-transitive across ASes

            Remaining 6 bits  : 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 all 8 octets
      of their encoding 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

6. Defined BGP Extended Community Types. Types

   This document 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 0x00: field, and the lower order octet
   (sub-type) is used to indicate a particular type of extended
   community.

6.1. Two-octet AS specific extended community

   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

    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
         0x00. 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 value format and meaning of the value encoded in
         this sub-field should be defined by the sub-type of the
         community.

      Type 0x01:

6.2. IPv4 address specific extended community

   This is an extended type with Type Field comprising of 2 octets and
   Value Field comprising 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
         0x01. either
   0x01 or 0x41. The low-order octet of this extended type is used to
   indicate sub-types.

   The Value field consists of two sub-fields. 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 information
         in this sub-field.  The value format and meaning of this value
         encoded in this sub-field should be defined by the sub-type of
         the community.

      Type 0x02:

6.3. Four-octet AS specific extended community

   This is an extended type with Type Field comprising of 2 octets and
   Value Field comprising 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x02 or 0x42  |   Sub-Type    |    Global Administrator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Global Administrator (cont.)  |    Local Administrator        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value of the high-order octet of this extended type is
         0x02. either
   0x02 or 0x42. The low-order octet of this extended type is used to
   indicate sub-types.

   The Value Field consists of two sub-fields. 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 format and meaning of the value encoded in
         this sub-field should be defined by the sub-type of the
         community.

      Type 0x03:

6.4. Opaque extended community

   This is an extended type with Type Field comprising of 2 octets and
   Value Field comprising 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
         0x03. either
   0x03 or 0x43. 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. sub-fields.

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

6.

7. 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 low-
   order octet of the extended
   type Type field for this community is 0x02.

   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 which is administered by the organization to which
   the Autonomous System number carried in the Global Administrator
   subfield 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 in contains a number from a numbering
   space which is administered by the Value Field MUST be unique
   within organization to which the Autonomous system IP
   address carried in the Global Administrator sub-
   field.

7. subfield has been
   assigned by an appropriate authority.

8. 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 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 low-
   order octet of the extended
   type 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 which is administered by the organization to which
   the Autonomous System number carried in the Global Administrator
   subfield 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 in contains a number from a numbering
   space which is administered by the Value Field MUST be unique
   within organization to which the Autonomous system IP
   address carried in the Global Administrator sub-
   field.

8. subfield has been
   assigned by an appropriate authority.

9. 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 Link Bandwidth Community is marked as non-transitive, then the of an extended type.

   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 Type field for this community is
   0x04.

   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.

10. 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 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 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 which contains the set union of all the
   Extended Communities from all of the aggregated routes. The default
   behavior could be overriden 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.

   A BGP speaker should not SHOULD NOT propagate a non-transitive extended
   community across the Autonomous system boundary. However, a BGP
   speaker SHOULD propagate a non-transitive extended community across
   the BGP Conferederation 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.

11. IANA Considerations

   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 value
   of the high-order 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).

   For the high-order octet of the Type Field, values 0x00 through 0x03
   and 0x40 through 0x43 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 and 0x44-0x7f for regular types
   (0x0400-0x3fff and 0x4400-0x7fff 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 Type Field values 0x0000-0x0001, 0x0005-0x00ff,
   0x0100-0x0101, 0x0104-0x01ff, 0x0200-0x0201, 0x0204-0x02ff 0x0204-0x02ff,
   0x0300-0x03ff, and 0x0300-0x03ff 0x4000-0x43ff are to be assigned by IANA, using
   the "First Come First Served" policy defined in RFC 2434.

   The Type Field values 0x80-0xbf 0x90-0xbf and 0xd0-0xff for regular types
   (0x8000-0xbfff
   (0x9000-0xbfff and 0xd000-0xffff when expressed as extended types)
   are vendor-specific
   types, and values to be assigned by IANA, using the "IETF Consensus" policy defined
   in this range RFC2434.

   The Type Field values 0x80-0x8f and 0xc0-0xcf for regular types
   (0x8000-0x8fff and 0xc000-0xcfff when expressed as extended types)
   are experimental, and are not to be assigned by IANA.

11.

12. Security Considerations

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

12.

13. Acknowledgements

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

13.

14. 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.

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

15. 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