Hi, Ryan.
The UDP capabilities in PingPlotter are similar to the unix Traceroute command. The unix traceroute command uses a moving target port (starting at 33434) and changes the target port to be able to distinguish between packets. We rely on the fact that the targeted server will respond with a "Port Unreachable" command as well.
This means we cannot target a single port, or one that answers with a response other than "Port unreachable". These same limitations apply to most other UDP traceroute applications as well.
Our TCP implementation, though, can target a specific port - but only with the TCP packet type.
We're investigating adding some additional UDP capabilities in the future, but haven't done so yet.
Thanks for the question.
- Pete