The counterpart of TCP/IP port forwarding is detecting which of them are open.
There are many tools for that.
Locally, you can use netstat to see what processes are listening on what ports.
Remotely you can use the Microsoft PortQry as a basic tool on Windows, or the multi platform the nmap (console) / zenmap (UI) combo to go very advanced.
On Windows, nmap (like wireshark) uses WinPcap for pcap packet capturing.
–jeroen
