First, make sure you've configured Cerberus FTP Server to be visible on the Internet. Assuming you are connecting through the Internet through a router, you will need to use your router IP address. Cerberus will automatically detect it and display it at startup as the 'WAN IP' address in the screen log. It should be the first thing listed when Cerberus FTP Server starts up, assuming you have 'Detect WAN IP at Startup' enabled from the 'General' tab of the Server Manager.