What is a port in networking?
A port is a numbered service endpoint on an IP address. It lets many applications share one host while still directing traffic to the right service.
- Why ports exist.
- Why HTTPS uses 443 and HTTP uses 80.
- How port state affects diagnostics and troubleshooting.
How ports work
An IP address identifies the host or network endpoint. The port identifies the service on that host.
That is why 203.0.113.10:443 and 203.0.113.10:22 can mean completely different applications.
Common examples
80 is commonly HTTP.
443 is commonly HTTPS.
22 is commonly SSH.
What a scan tells you
Open means a listener accepted the connection.
Closed means the host rejected it because nothing answered there.
Filtered means the result was obscured by a firewall or timeout.
Why it matters
Correct interpretation helps you distinguish between service state, firewall policy, and routing problems.
A port scan by itself does not prove a service is healthy or safe.
Is an open port bad?
Not by itself. It depends on whether the service should be reachable and whether it is secured.
Can one host have many open ports?
Yes. A single host can expose multiple services at the same time.
Last updated: March 29, 2026