Very annoying. What happens is, every now and then when i enter into left4dead 2, the connection resets. Particularly when i'm loading or searching for servers.

I've tried:

Open ports for Steam and Left 4 Dead 2
Set launch option: +mm_server_search_inet_ping_window 0

The second has made the game somewhat playable, but i still wish to make this a rare occurence. I can't tell if the first has made things better.