query about determining ingress interface

[Rajesh Talpade]

Hi 

Is there a way for an ISP to determine the ingress router interface at 
its network border that will carry IP traffic _from_ an IP address not 
owned by it?

I don't want to assume the path is the same in both directions, and tools
such as CAIDA's skitter plot paths from specific sources. One approach
might be deriving network paths from CAIDA's data, perhaps someone has
already done this? 


Thanks.
Rajesh.