Hey, i guess i had the same problem. You have to set you local machines ip, not your external. For example if you have windows type "ipconfig /all" in your cmd window. There you can see all your network connections. Now you have to find you internetconnection, for example lan 3 or something like this. There you have the prefered ipv4. Try running your server with this ip
Your external ip, the one you can see at "whatismyipaddress.com" for example is your external ip. This one is for you friends who want to join your server
Hope it works