So I set everything up on my old Thinkpad running the newest Ubuntu Server OS and I can play on the server within my own network. Now I want my friends to join, thus i tried to forward the port 25565 via my routers routerlogin.net site (Netgear R6120). I set up a Port forward everything and started the server in the webui, but my friends cant join. When I check the port on Open Port Check Tool - Test Port Forwarding on Your Router it says that the port is closed. How can I fix that?
Additional information: Firmware V126.96.36.199, connectet to a modem