What is the range of TCP/UDP ports?

TCP and UDP use the same port range: from 0 to 65535. The difference between TCP and UDP is that they have different port spaces.

In short: TCP port 80 and UDP port 80 are different ports.

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#Overall port range

• Minimum: 0
• Maximum: 65535
• Total: 65,536 ports for TCP and the same number for UDP

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#Main port ranges

#1. Well-known ports (0-1023)

Standard, "well-known" ports.

Used by basic network services:

• 80 - HTTP
• 443 - HTTPS
• 22 - SSH
• 25 - SMTP
• 53 - DNS

Usually:

• require administrator privileges
• used by servers

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#2. Registered ports (1024-49151)

Ports assigned to specific applications.

• used by servers and services
• not considered system ports

Examples:

• 3306 - MySQL
• 5432 - PostgreSQL
• 8080 - alternative HTTP

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#3. Dynamic / Ephemeral ports (49152-65535)

Temporary (dynamic) ports.

Used by:

• client applications
• assigned automatically by the OS
• exist only for the duration of the connection

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#Important points for the interview

• the ranges are the same for TCP and UDP

• the port spaces are separate

• a port is part of an end-to-end connection

• a connection is uniquely identified by the set:

  Copy

  source IP + source port + destination IP + destination port + protocol (TCP/UDP)

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#In short, for the interview

The range of TCP and UDP ports is 0 to 65535. It is divided into well-known (0-1023), registered (1024-49151), and dynamic/ephemeral (49152-65535); TCP and UDP have independent port spaces.