Single carrier multi-circuit asynchronous routing issue

Wed Jan 7 19:53:25 UTC 2009

I am curious to know if anyone has else has hit a problem like the one I 
am running into right now.

I have two DS3 DIA's in my router, terminating on two separate routers 
at Sprint. We peer with BGP and I am prepending certain of my prefixes 
to balance the traffic load.

src			 __________		   dst
1.1.1.0 |----|- ds3 #1 -| sprint 1 |--(          ) 2.2.2.0
------- |me  |                        ( internet ) -------
         |    |                        (          )
	|    |		 __________   (		 )
         |----|- ds3 #2 -| sprint 2 |--(          )

If I were to prepend the network 1.1.1.0 to come in on 'sprint 1', but 
have a route to 2.2.2.0 via 'sprint 2' so that traffic comes in on one 
circuit but returns on the other, routing is broken. If I change my 
route so that packets directed to 2.2.2.0 return on the same circuit 
that the traffic is received on, everything works fine.

Has anyone else run into an issue like this before?

-- am