Sockets, which are gateways to applications, are identified by a combination of an IP address and a 16-bit port number. That means

2

16

=

65536

2

16

=65536

port numbers exist. However, they start from port

0

0

so they exist in the range of

0

−

65535

0−65535

.

Sockets have associated port numbers!

Sockets have associated port numbers!

Out of these, the port numbers

0

−

1023

0−1023

are well-known and are reserved for certain standard protocols. Port

80

80

, for instance, is reserved for HTTP whereas port

22

22

is reserved for SSH.

Refer to page 16 of RFC 1700 for more details regarding what port number is assigned to what protocol.