Port forwarding means you have to forward some ports on your modem or router to your pc's internal ip address. so that you can contact to outside internet with those ports.
in order to know how to do this you need to know which modem or router you are using. because every modem or router has its own way to forward ports,
click here to get help with port forward on your modem / router.
in order to host any gaming server you need to forward specific ports, you can see the chart for ports for every game, and then forward relative ports on your router.
CS 1.6 Server Ports
which ports to forward in cs 1.6 server?
For CS 1.6, the ports you need to forward are:
Start: End: Protocol
1200 - 1200 UDP
27000-27015 UDP
27030-27039 TCP
How can you check if you port is forwarded or not?
click here to check now :)
Learn how to make a cs 1.6 server and get Pro in Gaming
