In a typical Cisco router it's possible to ping a host from the router's OS. When the ping packet leaves router (call it R1) through the fa0/0 interface, the source IP of that packet it set to the IP of fa0/0, right?
Is it possible to specify the interface of R1 I want the ping packet to go through? Different interfaces = different source IPs.
I know that usually there's only one way to the destination, but still. I'm not even sure if it's possible, because we would need to somehow make the router ignore its routing table - simply because the routing table gives a router exact information where to send the packet to, there can't be two 'matching' entries with identical priority in the table.