I used to host a listen server with a NETGEAR router with the ports 27015 & 27005 (if I remember correctly) both UDP/TDP.
Now, since the NETGEAR router’s ability to provide wireless signal went out, I can no longer use it. Thus, I got a new one. I searched the ocean of Google for answers before, during, and after the process of [trying] making a listen server work again.
My current router is a DLINK DIR-165 — Firmware Version : 9.00NA , 25, Nov, 2011 —
This is what the control panel for port forwarding looks like with my current settings. I DID use the following: 27015 & 27015 , 27015 & 27005.