Port, may be an application specific or process specific endpoint to a logical connection. This tells a way a client program specifies a specific server program on a computer in a network. The port acts as a contact port for an application or a process in the host system. Port numbers determine the logical endpoints of a connection.
Based on port numbers, ports are mainly classified as:
Well known port numbers – These are a subset of numbers which are assigned to the application. The server usually provides its service on a well-known port. Used in the range of 1 to 1023 and managed by IANA (Internet Assigned Numbers Authority).
Registered port numbers – These are also used by applications but in the range of 1024 to 65535. These are not managed by IANA.
Reserved port numbers – Port numbers in the range of 1 to 1023 are called reserved port numbers. Applications like Login, SSH etc use the reserved port numbers as a part of authentication between client and server.
Reserved port numbers
Port Number Application
1 TCP Port Service Multiplexer
22 SSH Remote Login Protocol
42 Host Name Server
69 Trivial FTP
118 SQL Services
156 SQL Server
546 DHCP Client
547 DHCP Server