if the servers on your computer, then for now turn on windows firewall (dont know about linux) but make sure ONLY needed ports are open.
21 for ftp (if u need it)
27015 (or wahtever your cs server port is)
and I THINK 80 for internet (i dont rememebr)
if windows firewall is running, if you start up cs or whatever it will give you a very annoying popup asking to unblock the port. if you see that you are good to go
vista - start>control panel>security>windows firewall> turn windows firewall on or off.
xp will be something like it, it should be easy to figure out by the directorys i gave ya for vista
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