Port forwarding is must for an "online" game server. You can read more about port forwarding at PortForward.com (link).
Because port forwarding is mostly done via web browsers, GUI makes things much easier for the user.
To forward ports, you must first know what your Default Gateway is. To find out this, open a command prompt from programs under Windows OS and type ipconfig and press Enter, it's there under the "Ethernet adapter".
Now that you know what it is, type your Default Gateway in the browser and press Enter.
It'll then, ask you for the login details. Provide those and proceed to the next step.
Note: You must know your router's username and password, without these you won't be able to access the admin panel.
Pro-tip: By default, username and password can be admin for both in most cases.
In there, search for NAT -> Virtual Servers under Advanced Setup, and Add following details:
Note1: Your order albeit may differ, but it should be more or less the same.
Note2: Sometimes port range can be like 27000-27020 or 27000:27020.
Reference picture:
It'll then, look like this (unless there's something else on the page already):
Note: You MUST click Save/Apply to changes take effect; it should be somewhere there.
Pro-tip: If you've trouble finding said location, you can always use DMZ host, it only requires CS 1.6 server IP address (not recommended).
To find out whether or not your port was forwarded properly, restart your router and computer (if possible) then launch your CS 1.6 server. Go to GameTracker, sign up for a free account and add your server IP there. If it says "We have added the server "SERVER_NAME" to your favorites servers for your convenience.", it means your server was added successfully.
That's all.
Because port forwarding is mostly done via web browsers, GUI makes things much easier for the user.
To forward ports, you must first know what your Default Gateway is. To find out this, open a command prompt from programs under Windows OS and type ipconfig and press Enter, it's there under the "Ethernet adapter".
Now that you know what it is, type your Default Gateway in the browser and press Enter.
It'll then, ask you for the login details. Provide those and proceed to the next step.
Note: You must know your router's username and password, without these you won't be able to access the admin panel.
Pro-tip: By default, username and password can be admin for both in most cases.
In there, search for NAT -> Virtual Servers under Advanced Setup, and Add following details:
- Custom Server: - name it so that you can easily recognise these ports if need be
Server IP Address: - the IP address on which the CS 1.6 server is hosted
External Port Start: - port range
External Port End: - port range
Note1: Your order albeit may differ, but it should be more or less the same.
Note2: Sometimes port range can be like 27000-27020 or 27000:27020.
Reference picture:
It'll then, look like this (unless there's something else on the page already):
Note: You MUST click Save/Apply to changes take effect; it should be somewhere there.
Pro-tip: If you've trouble finding said location, you can always use DMZ host, it only requires CS 1.6 server IP address (not recommended).
To find out whether or not your port was forwarded properly, restart your router and computer (if possible) then launch your CS 1.6 server. Go to GameTracker, sign up for a free account and add your server IP there. If it says "We have added the server "SERVER_NAME" to your favorites servers for your convenience.", it means your server was added successfully.
That's all.
I have my own CS server for the first time in 11+ years 
