Network Working Group D. Rao
Internet-Draft P. Mohapatra
Intended status: Standards Track Cisco Systems
Expires: April 24, 2009 J. Haas
Arbor Networks
October 21, 2008
Generic Subtype for BGP Four-octet AS specific extended community
draft-dhrao-idr-4octet-extcomm-generic-subtype-00.txt
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Abstract
Maintaining the current best practices with communities, ISPs and
enterprises that get assigned a 4-octet AS number may want the BGP
UPDATE messages they receive from their customers or peers to include
a 4-octet AS specific extended community. This document defines a
new sub-type within the four-octet AS specific extended community to
facilitate this practice.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Generic Subtype Definition . . . . . . . . . . . . . . . . . . 3
3. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
Maintaining the current best practices with communities, ISPs and
enterprises that get assigned a 4-octet AS number may want the BGP
UPDATE messages they receive from their customers or peers to include
a 4-octet AS specific extended community. This document defines a
new sub-type within the four-octet AS specific extended community to
facilitate this practice.
As an example, [RFC1998] describes an application of BGP community
attribute ([RFC1997]) to implement flexible routing policies for
sites multi-homed to one or multiple providers. In a two-octet AS
environment, the advertised routes are usually associated with a
community attribute that encodes the provider's AS number in the
first two octets of the community and a LOCAL_PREF value in the
second two octets of the community. The community attribute signals
the provider edge routers connected to the site to set the
corresponding LOCAL_PREF on their advertisements to the IBGP mesh.
In this way, customers can put into practice topologies like active-
backup.
When such a provider is assigned a four-octet AS number, the existing
mechanism of using communities is not sufficient since the community
value can not exceed four bytes. The natural alternative is to
extend the same mechanism using extended communities since it allows
for encoding eight bytes of information.
[] defines four-octet AS
specific extended community with a designated type field. At the
time of writing this document, there are two known sub-types defined:
Four-octet specific Route Target extended community and Four-octet
specific Route Origin extended community. This document specifies a
generic sub-type for the four-octet AS specific extended community to
provide benefits such as the one cited above as the Internet migrates
to four-octet AS space.
1.1. Requirements Language
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].
2. Generic Subtype Definition
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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 | 0x04 | Four-Octet AS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Four-Octet AS (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is a transitive extended community with Type Field comprising of
2 octets and Value Field comprising of 6 octets.
The high-order octet of this extended type is set to 0x02 as defined
in [I-D.ietf-l3vpn-as4octet-ext-community]. The low-order octet or
the sub-type is set to 0x04.
The Value Field consists of two sub-fields:
Global Administrator sub-field: 4 octets
This sub-field contains a four-octet Autonomous System number.
Local Administrator sub-field: 2 octets
This sub-field contains a value that can influence
routing policies. It is expected that the values
will be identical to the ones used in practice with standard
communities and will be of significance between the local
Autonomous System and its customer or peering Autonomous
Systems.
3. Deployment Considerations
A speaker with a 4-octet Autonomous System may have a customer or
peer with a 2-octet Autonomous System. If such a peer supports
4-octet extended communities, then it will be able to tag its routes
with the 4-octet extended community defined by the speaker. If the
peer does not support 4-octet extended communities, then the speaker
may need to define an appropriate standard community value for the
same purpose.
Similarly, a 2-octet AS may have two valid representations as either
a standard community or a 4-octet extended community with the upper
two octets of the AS set to zero. Therefore, as per
[I-D.ietf-l3vpn-as4octet-ext-community], two-octet ASes SHOULD use
standard 2-octet communities rather than 4-octet AS specific extended
communities in order to avoid inconsistencies.
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4. Acknowledgments
5. IANA Considerations
IANA is requested to assign sub-type 0x04 as a generic four-octet AS
specific extended community.
6. Security Considerations
There are no additional security risks introduced by this design.
7. Normative References
[]
Rekhter, Y., Sangli, S., and D. Tappan, "Four-octet AS
Specific BGP Extended Community",
draft-ietf-l3vpn-as4octet-ext-community-00 (work in
progress), September 2008.
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
[RFC1998] Chen, E. and T. Bates, "An Application of the BGP
Community Attribute in Multi-home Routing", RFC 1998,
August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Dhananjaya Rao
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: dhrao@cisco.com
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Pradosh Mohapatra
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: pmohapat@cisco.com
Jeffrey Haas
Arbor Networks
2727 S. State St.
Ann Arbor, MI 48104
USA
Email: jhaas@arbor.net
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