[Gllug] Advanced routing

[tet at accucard.com]

I've got a bit of a routing problem. Does anyone know if I can NAT/PAT
selectively depending on route? I have two routes to a given destination.
A primary (with a preferential metric) and a backup. The problem is that
the backup route won't accept traffic for a given IP address, but *does*
provide the same service on a different address.

So if the primary route is available, then I'd send the request straight
through. But if the route is down, I'd want to NAT to the backup route
to use the alternative IP address. Thus the change of routes is transparent
to the originating application.

Routing is currently done using Cisco IOS, but if a way to do this was
found, putting in an additional router running OpenBSD with ipf/pf or
Linux with iptables wouldn't be a problem. Of course, if anyone knows
how to do this natively in IOS, so much the better.

Tet

PS.  Yes, I know the obvious solution is to allow both routes to accept
     a single IP address, but they're managed by a third party, and we
     don't have control over them. To make it worse, they currently
     provide 6 services to us over the two leased lines. For 4 of
     those, we can use a single IP address, no matter which route
     we're taking. For the other two, we can't :-( So we know they
     *can* do it, they're just *not* doing it for those two...

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