What is the Port No?

A port number is a 16-bit integer that identifies a specific process or application running on a network-connected device. It's crucial for directing incoming network messages to the correct application. Think of it like a mailbox number for your computer—it tells the network exactly where to deliver data.

How Port Numbers Work

When a network message arrives at a server or device, the port number guides the operating system to the appropriate application. For example, web servers typically use port 80 (HTTP) or 443 (HTTPS). Each application has a designated port number. These ports are standardized, meaning that commonly used applications have established port numbers, while others might use dynamic ports assigned during runtime.

• Example: If you type a website address in your browser, your computer sends a request to the web server's IP address and port 80 (or 443 for secure connections). The server then uses this port number to know which application (the web server software) should process the request.

Finding Your Port Number

The method for finding a specific application's port number depends on the operating system and the application itself. Some common approaches include:

• Using command-line tools: On Windows, netstat -a lists active connections, displaying the local port numbers. Similar commands exist for other operating systems (e.g., netstat -tulnp on Linux/macOS).
• Checking application settings: Many applications explicitly state the port they use in their configuration or settings.
• Consulting documentation: The documentation or support pages for specific applications often list their default or configurable port numbers.

Common Port Numbers

Some well-known port numbers include:

• Port 80: HTTP (Hypertext Transfer Protocol) – used for standard web browsing.
• Port 443: HTTPS (Hypertext Transfer Protocol Secure) – used for secure web browsing (encrypted).
• Port 22: SSH (Secure Shell) – used for secure remote login.
• Port 21: FTP (File Transfer Protocol) – used for file transfers.
• Port 23: Telnet – used for remote terminal access (less secure).

Important Note: Many other port numbers exist for various applications and services. A complete list can be found on websites like Wikipedia's List of TCP and UDP port numbers.