This will force War FTP Daemon to use the IP number you specified, in stead of all IP addresses it find on the machine.
Note: You must have a static IP address. If you are on a dialup connection, or another connection where the IP number change when you connect to the Internet, you can not use this feature! If you don't know what a static IP address is, you need to learn the basics about networks and the Internet before you set up a FTP server! If not, there is a great risk that you expose yourself, your machine and your network for all kind of exploits and network abuse!