When you’re tunneling ports behind NAT, it’s useful to know what ports you have open, and wether or not it’s working. Short of having a system outside of your firewall, there are relatively few safe ways of testing.

There are at least a few sites which offer similar utilities, however, they are usually capable of only testing a single port at a time, which is nearly impossible to use when testing a dynamic range of ports.

For this purpose, I’ve created my TCP port test utility.

Note that I’ve created a few safeguards so this system will not be abused:

• Only ports between 1024 and 65535 are allowed to be tested.
• A range of only 50 sequential ports are allowed to be tested at a time.
• You are only able to test the IP that the server sees you coming from.
• It uses a simple cookie system; if you block cookies, you won’t be able to use it.