Port Checker

What is Port Checking?

Port checking is the process of testing whether a specific network port on a host is open, closed, or filtered. Ports are numbered endpoints (1-65535) that services use for network communication. Checking ports helps identify which services are running, troubleshoot connectivity issues, and verify firewall configurations.

Our free Port Checker provides information about port checking and common ports. Note that browser JavaScript cannot directly check TCP ports due to security restrictions, so port checking requires server-side tools, command-line utilities, or specialized services.

Why Check Ports?

Port checking is useful for:

• Verifying service availability
• Troubleshooting connectivity issues
• Checking firewall configurations
• Identifying open ports for security
• Testing network configurations

Common Ports

• 80: HTTP (web traffic)
• 443: HTTPS (secure web traffic)
• 22: SSH (secure shell)
• 21: FTP (file transfer)
• 25: SMTP (email)
• 3306: MySQL database
• 5432: PostgreSQL database
• 27017: MongoDB database

Port States

• Open: Port is accepting connections
• Closed: Port is not accepting connections
• Filtered: Port is blocked by firewall

Best Practices

• Use Command Line: Use nc, telnet, or nmap for accurate results
• Check Firewalls: Verify firewall rules allow port access
• Security: Only open necessary ports
• Test Regularly: Periodically check port status

FAQs

Why can't I check ports from the browser?

Browser JavaScript cannot directly check TCP ports due to security restrictions. Use server-side tools, command-line utilities, or port checking services.

How do I check if a port is open?

Use command-line tools like nc (netcat), telnet, or nmap to check port connectivity. Online port checking services are also available.

What is a closed port?

A closed port is not accepting connections. This could mean the service isn't running or the port is blocked.

What is a filtered port?

A filtered port is blocked by a firewall or network filter, preventing connection attempts from reaching the port.

Is port scanning legal?

Port scanning your own systems is legal. Scanning systems you don't own may violate terms of service or laws. Always get permission before scanning.