[f-nsp] BGP design problem

Chris Cameron chris at upnix.com
Thu May 28 15:16:31 EDT 2009

We're using a BigIron RX4 with 2.7.0T143 installed.

We have two different ISP's (ISP A and B) coming into the same router.
We have two /24's, one is "dedicated" for ISP A, the other for ISP B.
Should ISP A go down however, the IP block "dedicated" to it can be
advertised out ISP B. Traffic is balanced across the two providers
through Akamai (content caching service), regardless of best route.

This setup as described creates a problem where incoming traffic comes
in on ISP A, but on the way out the router decides ISP B is the better
outgoing path. To better control our outgoing traffic, we're trying to
force traffic to stay on the ISP that it came in on.

So that summarizes the problem.

We've tried policy based routing, however after testing it seems that
it determines a route is dead based on link status, which isn't
helpful if an upstream router fails. Policy based routing would work
well if it determined a link was "down" based on a BGP route existing
or not.

We have two ideas that would likely work if we were using IOS, one is
virtualizing the router so that we have two routing processes. The
other is object tracking using IP SLAs.

Multi-VRF sounds like it would do virtualized routing, but it's only
listed as supported on the NetIron. I can find nothing like object
tracking in the Foundry world.

Any one have ideas based either on our problem, or regarding things we've tried?

Many thanks,


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