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What Is a Port?

A port is a numerical label used by a device’s operating system to direct incoming and outgoing network traffic to the right application or service. While an IP address identifies a device on a network, a port identifies which specific program on that device should handle a given connection. Together, they work like a building address and a suite number. 

Ports are numbered from 0 to 65535. Many are standardized: web browsers, for example, communicate over port 80 for HTTP and port 443 for HTTPS, while email and file transfer services use their own designated numbers. These well-known ports make it possible for software across different systems to reliably find and talk to each other. 

A firewall can control which ports are open or closed on a device, blocking unwanted traffic while allowing legitimate connections through. Port scanning is a technique used to check which ports on a device are active, commonly used by network administrators for security audits and by malicious actors to look for vulnerabilities.