Like a set of post office box numbers for the protocol
Each type of application gets a port number
Port number + host address gives it a unique identifier to send and receive
Over 65,000 valid port numbers
OS can support many applications at once
Warcraft : What ports need to be open?
In order to connect to Battle.net, connect to others over a Local Area Network,
and allow others to connect to games you create, the following ports need to
be opened.
Diablo, Warcraft II Battle.net Edition, and StarCraft:
* Ports 6112 through 6119 TCP & UDP