TCP Connections & Port Numbers

To uniquely identify a TCP connection, you need 4 things: Destination IP Address, destination Port Number, source IP Address, and source Port Number.

Port numbers are 16 bit integers, 0 through 65535 (2 to the 16 minus 1, like a byte is 255, can't represent 256) You can represent 256 unique values: 1 through 255 and 0.