The largest port number is an unsigned short 2^16-1: 65535
A registered port is one assigned by the Internet Corporation for Assigned Names and Numbers (ICANN) to a certain use. Each registered port is in the range 1024–49151.
Since 21 March 2001 the registry agency is ICANN; before that time it was IANA.
Ports with numbers lower than those of the registered ports are called well known ports; port with numbers greater than those of the registered ports are called dynamic and/or private ports.