Port Number - Basics

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

7                                                                     ECHO

20                                                                 FTP—Data

21                                                                 FTP—Control

22                                                                 SSH Remote Login Protocol

23                                                                 Telnet

24                                                                 SMTP

42                                                                 Host Name Server

49                                                                 Login

53                                                                 DNS

69                                                                 Trivial FTP

80                                                                 HTTP

109                                                              POP2

110                                                              POP3

118                                                              SQL Services

156                                                              SQL Server

161                                                              SNMP

389                                                              LDAP

443                                                              HTTPS

546                                                              DHCP Client

547                                                              DHCP Server