If you experience connectivity issues - such as disconnects, problems with connection to the game server or problems while accessing certain game modes, it is worth checking whether you have all ports used by the game open.

TCP 80, 8085, 5222
UDP Ports 64100 through 64299

Also, here is a list of server addresses, in case you wish to self-diagnose some situation with a particular server via command prompt commands (pathping, ping, tracert, etc.), or just measure your latency values to any of them: