Server.Jar crashing

 Please help, I have been having the same issue as my friend and we can't seem to find a way to fix the problem. We've tried to remaking the server multiple times, but it still crashes after 2 seconds of opening. I have played around with the files to see if there's anything wrong, but everything looked alright. The server.jar crashes only when I put my Default Gateway in the server-ip= in the Server Properties. When I put anything else or nothing, it doesn't crash, which is weird but it won't open the server if I don't put my ip.