Network Working Group P. Mohapatra
Internet-Draft R. Fernando
Intended status: Standards Track Cisco Systems
Expires: August 28, 2010 February 24, 2010
BGP Link Bandwidth Extended Community
draft-ietf-idr-link-bandwidth-01.txt
Abstract
This document describes an application of BGP extended communities
that allows a router to perform unequal cost load balancing.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Link Bandwidth Extended Community . . . . . . . . . . . . . . . 3
3. Deployment Considerations . . . . . . . . . . . . . . . . . . . 3
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 4
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1. Introduction
When a BGP speaker receives multiple paths from its internal peers,
it could select more than one path to send traffic to. In doing so,
it might be useful to provide the speaker with information that would
help it distribute the traffic unequally based on the cost of the
external (DMZ) link. This document suggests that the external link
bandwidth be carried in the network using a new extended community
[RFC4360] - the link bandwidth extended community.
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. Link Bandwidth Extended Community
When a BGP speaker 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 is optional non-transitive. A border router MUST strip the
link bandwidth community from a route when it advertises the route to
an external neighbor. The value of the high-order octet of the
extended Type Field is 0x40. The value of the low-order octet of the
extended type field for this community is 0x04. The value of the
Global Administrator subfield in the Value Field SHOULD represent the
Autonomous System of the router that attaches the Link Bandwidth
Community. If four octet AS numbering scheme is used [RFC4893],
AS_TRANS should be used in the Global Administrator subfield. 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 subfield of the Value Field.
3. Deployment Considerations
The usage of this community is restricted to the cases where BGP
multipath can be safely deployed. In other words, the IGP distance
between the load balancing router and the exit points should be the
same. Alternatively, the path between the load sharing router and
the exit points could be label switched. If there are multiple paths
to reach a destination and if only some of them have link bandwidth
community, the receiver should not perform unequal cost load
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balancing based on link bandwidths.
4. Acknowledgments
The authors would like to thank Yakov Rekhter, Srihari Sangli and Dan
Tappan for proposing unequal cost load balancing as one possible
application of the extended community attribute.
5. IANA Considerations
This document defines a specific application of the two-octet AS
specific extended community. IANA is requested to assign a sub- type
value of 0x04 for the link bandwidth extended community.
Name Value
---- -----
non-transitive Link Bandwidth Ext. Community 0x4004
6. Security Considerations
There are no additional security risks introduced by this design.
7. Normative References
[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.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
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Authors' Addresses
Pradosh Mohapatra
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Phone:
Email: pmohapat@cisco.com
Rex Fernando
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Phone:
Email: rex@cisco.com
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