Internet DRAFT - draft-ietf-idr-link-bandwidth
draft-ietf-idr-link-bandwidth
Network Working Group P. Mohapatra
Internet-Draft Sproute Networks
Intended status: Standards Track R. Fernando
Expires: September 6, 2018 Cisco Systems
March 5, 2018
BGP Link Bandwidth Extended Community
draft-ietf-idr-link-bandwidth-07.txt
Abstract
This document describes an application of BGP extended communities
that allows a router to perform unequal cost load balancing.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Link Bandwidth Extended Community . . . . . . . . . . . . . . 2
3. Deployment Considerations . . . . . . . . . . . . . . . . . . 3
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
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 based on the bandwidth 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 an external neighbor and
advertises this route (via IBGP) to internal neighbors, as part of
this advertisement the router may carry the cost to reach the
external neighbor. The cost can be either configured per neighbor or
derived from the bandwidth of the link that connects the router to a
directly connected external neighbor. This value is carried in the
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Link Bandwidth Extended Community. No more than one link bandwidth
extended community SHALL be attached to a route. Additionally, if a
route is received with link bandwidth extended community and the BGP
speaker sets itself as next-hop while announcing that route to other
peers, the link bandwidth extended community should be removed.
The extended community is optional non-transitive. 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 [RFC6793], 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 (not bits!)
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. If the path between the load
sharing router and the exit point is not tunneled, then the IGP
distance between the load balancing router and the exit points should
be the same.
If the path between the load sharing router and the exit point is
tunneled, then the choice to use this community is a purely local
matter to the load sharing router.
In the context of BGP/MPLS VPNs [RFC4364], link bandwidth community
could be used to support inbound load balancing for multihomed sites,
as follows. Consider a site that is connected to PE1 and PE2. Both
PE1 and PE2 would advertise VPN-IP routes associated with the
destinations within the site. One way to enable other PEs to receive
all these routes is to require the RD of the routes advertised by PE1
to be different from the RD of the routes advertised by PE2. The
VPN-IP routes advertised by PE1 should carry the link bandwidth
community; likewise for the VPN-IP routes advertised by PE2. The
bandwidth value carried in the community could be locally determined
by PE1 and PE2. Alternatively CEs of the site, when advertising IP
routes to PE1 and PE2, could add the link bandwith community to these
advertisements, in which case PE1 and PE2, when originating VPN-IP
routes, would use the bandwidth value from the IP routes they
received from the CEs to construct the link bandwidth community
carried by these VPN-IP routes.
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An ingress PE, when sending traffic to destinations within the site,
can use the bandwidth value carried in the community of the routes
advertised by PE1 and PE2 to perform load sharing, where some of the
traffic would go via PE1, while other traffic would go via PE2.
If there are multiple paths to reach a destination and if only some
of them have link bandwidth community, the load sharing router should
not perform unequal cost load 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.
The authors would like to thank Bruno Decraene, Robert Raszuk, Joel
Halpern, Aleksi Suhonen, Randy Bush, and John Scudder for their
comments and contributions.
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,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
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[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/info/rfc6793>.
Authors' Addresses
Pradosh Mohapatra
Sproute Networks
Email: pradosh@sproute.com
Rex Fernando
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: rex@cisco.com
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