I have been testing with PRO on both ends and trying to convert the remote end to Agent. As you said, all I need in response is "port unreachable". I used 53/UDP because it was one of your standard configs. I was able to override your packet size by using the custom setting. I just need to use a single user-defined UDP port instead of a range of UDP ports to make my firewall team happy. I can change off of 53/UDP if I have to but it will require more change control/reviews.

Can you explain PacketType=ExternalCom? All the other parameters make perfect sense.