My fibre modem, is also a router. But since it only allows me to add 1 port not a port range to port forwarding and a total of around 30 port forwarding slots it wasnt enough for me. So i had to set the server to DMZ, fully exposed to the internet(i tought). This did not work, so i set the modem/router to bridge mode, and got a second router Netgear RX500, then added the port forwarding using the new router. Then it worked.