When running Ethereal, I can see the receiver making a broadcast looking for my PC. The message says something like, "Who is <PC's IP>? Tell <Receiver's MAC>". Then I see the the PC sending a broadcast, "Who is <Recevier's IP>? Tell <Ethernet cards MAC>". The order may be reversed, but that does occur. Then I see UDP messages coming from my PC on port 18678 to the receiver's port 18678. Then I get the destination unreacheable (code 3 - invalid port) where the source is the receiver 18678 and the destination is the PC 18678.