Okay.. So i was looking around, many people didn't know how. It's simple: Port Forwarding/Open Host.
So first.. go to your router options.. Open webbrowser, and type in your IP/DNS server ( mine = 192.168.2.1 ). Log in.
If you need a password, it should be admin or just leave it blank.
When you're in, go (advanced) Settings > Internet > Adress Translation NAT > Port forwarding.
At least, thats how it goes on my router. It's a Siemens Gigaset thingy.
Then open up the ports: TCP 27014 + 27050 , UDP 1500, 3005, 3101, 27000-27030, 28960 .
Safe it, restart router. then it should work. If it doesnt and your router has Exposed host: Just click that, enter the IP Adress of exposed host. Than it will automaticly have open NAT for everything.
I hope it will work! (Port forwarding does not work on my router, only exposed host)
Good luck! And thank me if it works