[nsp] Choosing routes based on return destination

From: Michael K. Smith (mike@wackypackets.com)
Date: Wed Feb 27 2002 - 20:09:45 EST


Hello All:

I am in the interesting position of building a cross-AS relationship where
two providers are buying bandwidth from one another. Sounds strange, but
each provider will use the other's upstream providers.

So, I need to figure out how to separate each provider's traffic onto a
separate port for billing purposes. That is, if I send traffic from
Source A to the Internet through Source B via Pipe 1, that traffic has to
return through Pipe 1. The same goes for Source B sending and receiving
its traffic over Pipe 2.

Gettting the outbound traffic to prefer a particular pipe is no
problem. All of the incoming provider routes are community-tagged, so I
can specifically announce the necessary routes over the correct
pipe. However, BGP doesn't really help on the return path, because each
provider will hear about the other's routews via both Pipe 1 and Pipe 2.

I'm thinking about using route maps to associate the return traffic coming
in via a transit provider destined to the remote to prefer the correct
link. However, the cross-connections between the two providers isn't on
the same routers as the various upstream providers, so I'm trying to
figure out how to do it without having to build circuits all the way
through to each of the border routers on either side.

If anyone has any tried and true methods, or even some interesting ideas,
I'd love to hear them.

Mike



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