If you notice the SERVER code I posted in the previous post,I only specified LocalPort. Since LocalAddr/LocalHost was NOT specified, that socket would bind to all available IP addresses, internal and external. So - it is listening on all interfaces. I have tested it for both cases, and it works fine.

For the CLIENT code, the PeerAddr determines which IP the datagram is sent to. You can send it to a local (127.0.0.1), external (normal IP), or broadcast address.

Hope this helps.