you need to open the ports for steam multiplayer and only for the one hosting the server. This is directly from steampowered.com
Required Ports for Steam
Question
Which ports do I need to open on my router or firewall for Steam?
Answer
Your network must be configured to allow Steam access to the following ports (in order from highest to lowest priority for QoS users):
Steam Client
UDP 27000 to 27015 inclusive (Game client traffic)
UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
TCP 27014 to 27050 inclusive (Steam downloads)
UDP 4380
Dedicated or Listen Servers
TCP 27015 (SRCDS Rcon port)
Steamworks P2P Networking and Steam Voice Chat
UDP 3478 (Outbound)
UDP 4379 (Outbound)
UDP 4380 (Outbound)
Additional Ports for Call of Duty: Modern Warfare 2 Multiplayer
UDP 1500 (outbound)
UDP 3005 (outbound)
UDP 3101 (outbound)
UDP 28960
UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
those are the ones i think you have to open. My router doesn't open ports correctly so I end up disconnecting my router and connecting only with my modem if i want to host a server. because theres no ports to worry about on the modem it works fine.
GL!:yes:
Edit: BTW! Kick ass Ed GIF Lol!