Having problems with your Network Connectivity caused by ArmA then read this!
Problems that may be fixed:
Nothing showing up on server list
Inability to load webpages after hosting or server browsing
Windows telling you that "Your computer is experiencing connectivity issues" or something similar
After GameSpy was removed from ARMA 3, a steam browser was implemented. There is nothing really wrong with it and it is a CLIENTSIDE setting that causes all the problems. Your system is pinging the steam gamebrowser sometimes up to 5000 times per minute, even if you have a super-buff internet connection- it can still cause issues.
Go to your Steam Settings via the top left link on your main steam page
Select "Ingame Settings" and change the server max pings per minute to 500 or lower.