What is a network port?
A port is a numbered endpoint that lets one server run many services on one IP. Learn common ports and check if one is open free.
A network port is a number (0–65535) that identifies a specific service on a machine. An IP address gets you to the computer; the port gets you to the right program running on it — web, email, SSH, and so on.
Why ports exist
A single server hosts many services at once. Ports let them share one IP address without collision: the operating system routes an incoming connection to whichever program is listening on that port. Ports 0–1023 are "well-known" and reserved for standard services.
Common port numbers
80 is HTTP, 443 is HTTPS, 22 is SSH, 25/587 are SMTP (email), 53 is DNS, 3306 is MySQL, 5432 is PostgreSQL. Knowing these helps when you check whether a service is reachable — if 443 is closed, the site’s HTTPS is not accepting connections.
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