Network Working Group D. Rao
Internet-Draft P. Mohapatra
Intended status: Standards Track Cisco Systems
Expires: April 29, 2010 J. Haas
Arbor Networks
October 26, 2009
Generic Subtype for BGP Four-octet AS specific extended community
draft-ietf-idr-as4octet-extcomm-generic-subtype-01.txt
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Abstract
Maintaining the current best practices with communities, ISPs and
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enterprises that are 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Generic Sub-type Definition . . . . . . . . . . . . . . . . . . 3
3. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
Maintaining the current best practices with communities, ISPs and
enterprises that are 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.
For 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 AS portion
of the RFC 1997 community cannot exceed two bytes. The natural
alternative is to extend the same mechanism using extended
communities since it allows for encoding eight bytes of information.
[] defines a format for a four-
octet AS specific extended community with a designated type field.
That document defines two sub-types: 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 Sub-type 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 or 0x42 | 0x04 | Global |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrator | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is an extended type 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 either 0x02 (for
transitive communities) or 0x42 (for non-transitive communities).
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. This value has semantics that are of significance for
the Autonomous System in the Global Administrator field.
3. Deployment Considerations
There are situations in peering where a 4-octet AS specific generic
extended community cannot be used. A speaker with a 4-octet AS may
not support 4-octet extended communities; or the speaker may have a
customer or peer that does not support 4-octet extended communities.
In all such cases, the speaker may need to define an appropriate
standard community value for the same purpose. As an example, a peer
may tag its routes with communities that encode AS_TRANS [RFC4893] as
the first two octets.
Similarly, a 2-octet AS number may have two valid representations as
either a standard community or a 4-octet extended community with the
upper two octets of the AS number set to zero. For backward
compatibility with existing deployments, and to avoid inconsistencies
between standard communities and 4-octet extended communities, two-
octet ASes SHOULD use standard 2-octet communities as defined in RFC
1997 rather than the 4-octet AS specific community as defined in this
document.
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4. Acknowledgments
The authors would like to thank Paul Jakma, Bruno Decraene and Cayle
Spandon for their useful comments on the document.
5. IANA Considerations
This document defines a specific application of the four-octet AS
specific extended community. IANA is requested to to assign a sub-
type value of 0x04 for the generic four-octet AS specific extended
community.
This document makes the following assignments for the generic four-
octet AS specific extended community:
Name Value
---- -----
transitive generic four-octet AS specific 0x0204
non-transitive generic four-octet AS specific 0x4204
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-03 (work in
progress), March 2009.
[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.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
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[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Authors' Addresses
Dhananjaya Rao
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: dhrao@cisco.com
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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