A network port is a numbered logical endpoint (0-65535) used to route traffic to the correct application on a device. An open port is one where a service is actively listening for incoming connections. Closed ports reject connections; filtered ports are blocked by a firewall.
Port States Explained
| State | Meaning | Security Implication |
|---|---|---|
| Open | A service is listening and accepting connections | Attack surface - must be secured |
| Closed | No service is listening; host responds with RST | Low risk, port is not in use |
| Filtered | Firewall drops packets; no response | Good - attacker cannot even confirm host existence |
What Happens If You Have Open Ports?
Open ports are not inherently dangerous - your web server needs ports 80 and 443 open. The risk comes from:
- Services that are open but not needed (unnecessary attack surface)
- Services running outdated, vulnerable versions
- Services with weak authentication (default passwords, no 2FA)
- Development services accidentally left open (debug ports, databases)
Should Port 80 and 443 Be Open?
Yes, if you are running a web server. These are the standard HTTP and HTTPS ports that browsers use. Closing them would make your website inaccessible. If you are not running a web server, they should be closed.
What Happens If Port 22 Is Open?
Port 22 is SSH (Secure Shell). If it is open and exposed to the internet, your server will receive automated brute-force login attempts within minutes. Mitigate by: using SSH key authentication only (disable password auth), moving SSH to a non-standard port, and using fail2ban or a firewall allowlist.
How to Check Your Open Ports
Use our Port Scanner to scan your own public IP from the outside, as an attacker would see it.
People Also Ask
- What are open ports used for?
- Open ports allow applications to accept incoming network connections. Web servers use 80/443, mail servers use 25/587/993, remote desktop uses 3389, and so on.
Related: Port scanning | Firewalls | Port Scanner