From TM Wiki

You will need to find out your IP address using a site such as http://www.whatismyip.org/

You can add this to your advanced network options screen. (Configure > Advanced > Network > Force Server Address.

If you have a Static IP this will not change but most Internet service providers use Dynamic IP addresses which change over time. It is best to keep checking to see if the IP you have entered is still correct.

Check you have Port Forwarding set up correctly.

To do ...