Network Working Group Srihari Ramachandra
Internet Draft Daniel Tappan
Expiration Date: March 2000 cisco Systems
BGP Extended Communities Attribute
draft-ramachandra-bgp-ext-communities-02.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.
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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 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
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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.
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.
The Type field for the Route Origin Community is 0x0001 or 0x0101.
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.
The Type field for the Route Target Community is 0x0002 or 0x0102.
7. 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.
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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.
8. Security Considerations
This extension to BGP does not change the underlying security issues.
9. Acknowledgements
To be supplied.
10. 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.
11. 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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