Common Ports: What Runs Where
This reference explains what runs on each TCP and UDP port and whether it belongs on the public internet. Search by port number or service name to identify what you found in a scan, a firewall log, or a netstat listing.
Port scanning is essential for network administrators, security professionals, and system operators. It helps identify exposed services, verify that only necessary ports are accessible, and test firewall rules.
Understanding Port States
Open: A service is listening and accepting connections.
Closed: The port is accessible but no service is listening. Connection was refused.
Filtered: A firewall or filter is blocking access. No response was received within the timeout.
Common Ports & Services
Port 22 (SSH): Secure shell for remote server access.
Port 80 (HTTP): Standard unencrypted web traffic.
Port 443 (HTTPS): Encrypted web traffic (SSL/TLS).
Port 25 (SMTP): Email sending protocol.
Port 3306 (MySQL): MySQL database connections.
Port 3389 (RDP): Windows Remote Desktop.
Security Best Practices
• Close all unnecessary open ports
• Use a firewall to restrict access to essential services
• Keep all services updated with security patches
• Use fail2ban or similar to prevent brute force attacks
• Monitor port access logs for suspicious activity
FAQ
Is port scanning legal?
Port scanning your own systems is legal. Scanning third-party systems without permission may violate computer crime laws in many jurisdictions. Only scan hosts you own or have explicit permission to test.
Why are my ports showing as filtered?
Filtered ports indicate a firewall is dropping packets without response. This is often the default behavior for ports that are blocked—more secure than actively refusing connections.