posted 11 years ago
Hi Jochem,
the sender IP usually depends on the routing table(s) and network configuration of your OS. The network stack decides which interface to use for sending your packets based on the routing table and the IP address of this interface is automatically used as sender IP. This can be changed though. With Linux for example you can use an iptables postrouting rule to modify the sender IP just before the network packets leave your box. There are surely similar approaches for any modern OS.
Marco