SRCDS Port Forwarding Issues

[elgo2006]

I recently built a new computer and decided to repurpose my old computer as a dedicated game server for me and some friends. I'm fairly new at all of this stuff, so I've run into a problem.

I downloaded the necessary files from SteamCMD to host a couple different game servers and was testing out connection using a dedicated GMod server (ran ./srcds_run -console -game garrysmod +maxplayers 8 +map gm_construct). I was able to connect to it no problem from my computer on the same network (no need for port forwarding), but when I invited my friend, he got the server not responding message.

These are the current ports that I have forwarded:

http://s16.postimg.org/uxk6mb9ut/ports.png

For some reason, those don't work. I set my server into DMZ mode for a couple minutes and he was able to join, leading me to believe that it's an issue with the ports.

Does anyone have a clue what's causing this? Am I missing a port or two? Any and all help is much appreciated.

[thorlax]

What's your srcds or srcds_run launch line look like?