What is a network port?

A network port is a number that identifies which service on a device a connection is meant for, so that one computer can run a web server, an e-mail server and remote access at the same time. Common examples: port 443 for secure websites, 22 for SSH remote administration, 3389 for remote desktop and 445 for file sharing. A port is called open when a service is listening on it. Open ports exposed to the internet are a common entry point for attackers, which is why you should know which ones you have. A port scan is someone checking many ports to find open ones.

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