Quote:A port scan is a bit like jiggling a bunch of doorknobs to see which doors are locked. The scanner learns which ports on a router or firewall are open, and can use this information to find a computer system’s potential weaknesses.

What’s a Port?

When a device connects to another device over a network, it specifies a TCP or UDP port number from 0 to 65535. Some ports are used more frequently, however. TCP ports 0 through 1023 are “well-known ports” that provide system services. For example, port 20 is FTP file transfers, port 22 is Secure Shell (SSH) terminal connections, port 80 is standard HTTP web traffic, and port 443 is encrypted HTTPS. So, when you connect to a secure website, your web browser is talking to the web server that’s listening on port 443 of that server.

Services don’t always have to run on these specific ports. For example, you could run an HTTPS web server on port 32342 or a Secure Shell server on port 65001, if you liked. These are just the standard defaults.