Well-Known Port Numbers: FTP, TELNET, HTTP, and More

This document describes well-known port numbers as defined in RFC 1700. It specifically covers port numbers for FTP, TELNET, HTTP, SMTP, POP3, IMAP, BIOS, SSH, and DHCP, all used within TCP, UDP, and IP protocols.

Port Numbers: The Basics

The endpoint of a logical network connection is known as a port. It’s essentially a 16-bit number, giving us a range from 0 to 65536.

The port numbers ranging from 0 to 1024 are designated as well-known ports. These are reserved for specialized or privileged services. For instance, as detailed in the table below, port 80 is commonly used for HTTP, while FTP typically uses port 21.

Table of Port Numbers for Common Protocols

Port numbers are pre-assigned by the Internet Assigned Numbers Authority (IANA). Their specifications are documented in RFC 1700.

The following table lists port numbers commonly used for FTP, TELNET, HTTP, SMTP, POP3, IMAP, BIOS, SSH, and DHCP. These protocols are fundamental to TCP or UDP connections within computer networks.