[c-nsp] Sending traffic over different paths

[Kristofer Sigurdsson]

Hi,

I was wondering if anyone on the list had any suggestions on how to
implement the following:

Let's say I've got two routers.  Both 7606, Sup720-3BXL, IOS
12.2(18)SXD advanced IP services.

Now, those two routers have two direct links between them.  One of
them is the upstream router for the other one, to our backbone, like
this:
                                            _______
           ___Link B____           /             \
          /                      \        /               RTR_C
RTR_A                      RTR_B              RTR_D
          \____________/         \_______/
                Link A

Now, what I want is:

Traffic to and from peers via RTR_D (identified by source IP addresses or BGP
communities) use Link A to go to and from RTR_A.

Traffic to and from peers via RTR_C (identified by a default route or
BGP communities) use Link B for traffic to and from RTR_A.

Should either Link A or Link B go down, all traffic goes through the other one.

Now, manipulating traffic *from* RTR_A is easy.  I'll just announce a
default route on both sides, with a higher metric on Link A, and the
more specific prefixes just on Link A, so they will disappear if Link
A goes down, and if Link B goes down, the higher metric default route
on Link A gets used.

The traffic from RTR_B to RTR_A is a tougher case.  Maybe policy
routing, but is that flexible enough to allow me to "break" the
policies in case of link failures?

Thanks in advance for any input,
Kristo