Computers communicating with each other use port numbers to select different applications. On the destination computer running the application the ports are assigned as follows:-
  • Well Known Ports - from 0 through 1023
  • Registered Ports - from 1024 through 49151
  • Dynamic and/or Private Ports - from 49152 through 65535
The source computer, requesting the application, dynamically assigns its own port numbers usually using numbers greater than 1023.
The Well Known Ports, in the range of 0-1023, are considered public port numbers and are controlled by the Internet Assigned Numbers Authority (IANA). The table in the next section lists the port numbers for some of the most common applications.

Common Well-Known Port Numbers

Port Number Assignment Explanation
20 FTP - Data File Transfer Protocol
21 FTP - Control File Transfer Protocol
22 SSH Secure Shell
23 Telnet Terminal emulation protocol
25 SMTP Simple Mail Transfer Protocol
42 DNS Name Servers
53 DNS Domain Name Protocol
69 TFTP Trivial File Transfer Protocol
80 HTTP Hypertext Transfer Protocol, Web pages
110 POP3 Post Office Protocol
161 SNMP Simple Network Management Protocol
443 HTTPS Secure HTTP, secure Web pages
520 RIP Routing Information Protocol
6667 IRC Internet Relay Chat

For further information see Port Numbers assigned by IANA

RFC 1700. Index

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(c) Compiled by B V Wood.

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