TechDudeTF2 servers are only accessible on one port.
This is typically 27015 (but can be changed for a given server). The dedicated only listens for connections on this port.
Now if you are interested in what ports are being used during gameplay you can use wireshark and inspect the packets being sent to the tf2 server: http://www.wireshark.org/
It's also possible that the server listens on 27015 but actually communicates to each client on a different port. Wireshark would show you this.
Literally a tech dude