Port Checker - Free Online Tool

A port checker is an online tool that tests whether specific network ports are open, closed, or filtered on a given IP address or domain name. It works by attempting to establish a TCP connection from an external server to the target port, simulating how external users would connect to your network services.

Port checkers help you verify if web servers, databases, remote access services, or other network applications are accessible from the internet. They are essential tools for network administrators, developers, and IT professionals who need to diagnose connectivity issues, audit security configurations, and ensure services are properly exposed.

TCP (Transmission Control Protocol): TCP is a connection-oriented protocol that ensures reliable, ordered delivery of data. It establishes a connection before transmitting data and includes error checking and retransmission of lost packets. TCP ports are used for applications that require guaranteed delivery, such as web browsing (HTTP/HTTPS), email (SMTP), file transfer (FTP), and remote access (SSH, RDP). Most port checkers, including ours, test TCP ports.

UDP (User Datagram Protocol): UDP is a connectionless protocol that sends data without establishing a connection first. It's faster but doesn't guarantee delivery or order. UDP ports are used for real-time applications where speed is more important than reliability, such as DNS queries, video streaming, online gaming, and VoIP services. UDP port checking is more complex because UDP doesn't send acknowledgment responses like TCP.

The main difference is reliability: TCP ensures data arrives correctly, while UDP prioritizes speed. Most common network services use TCP ports, which is why port checkers primarily focus on TCP port testing.

Port checking serves several critical purposes for network management and troubleshooting:

Security Auditing: Identify open ports that could expose your network to unauthorized access. Regular port checking helps detect unexpected services, verify firewall configurations, and ensure only necessary ports are accessible, reducing your attack surface.

Troubleshooting Connectivity: Diagnose connection problems by verifying port accessibility. When services aren't working, port checking helps determine if issues stem from firewall blocks, service failures, or network misconfigurations.

Service Verification: Confirm that web servers, databases, APIs, and remote access services are properly configured and reachable from external networks. This is essential during deployment and maintenance to ensure services are live and functioning.

Network Configuration: Verify router port forwarding rules, test ISP port blocking, and validate network setup for hosting services. Port checking guides proper firewall and router configuration.

Compliance and Monitoring: Maintain audit trails of port status changes, ensure compliance with security policies, and monitor network accessibility over time.

Port checkers provide highly accurate results when testing TCP ports, as they use the same connection methods that real applications would use. However, several factors can affect accuracy:

Network Conditions: Temporary network issues, high latency, or packet loss can cause false negatives (showing a port as closed when it's actually open). Running multiple checks can help confirm results.

Firewall Behavior: Some firewalls may respond differently to connection attempts, potentially showing ports as filtered when they're actually open to specific IP addresses or after authentication.

Service Status: Port checkers test port accessibility, not whether a service is running correctly. A port may be open but the service might be down or misconfigured.

Timing: Services that are starting up or shutting down may show inconsistent results. For critical decisions, verify results with multiple checks and consult your network administrator.

Our port checker uses reliable TCP connection testing methods and provides accurate results in most scenarios. For enterprise network decisions, we recommend combining port check results with internal network monitoring tools.

To open or close a port, you need to configure your firewall, router, and the service itself. Here's how:

To Open a Port:

• Start the service: Ensure the application or service that uses the port is running and listening on that port.
• Configure firewall: Add a firewall rule to allow incoming connections on the port. On Windows, use Windows Firewall; on Linux, use iptables, ufw, or firewalld; on routers, access the admin panel.
• Set up port forwarding: If behind a router, configure port forwarding to route external traffic on that port to your internal device.
• Check ISP restrictions: Some ISPs block certain ports. Contact your ISP if standard ports are blocked.

To Close a Port:

• Stop the service: Shut down the application or service listening on the port.
• Block with firewall: Add a firewall rule to deny incoming connections on the port, or remove existing allow rules.
• Disable port forwarding: Remove port forwarding rules on your router if they exist.
• Network isolation: Move the service to a network segment that isn't accessible from external networks.

Important: Only open ports that are necessary for your services. Each open port is a potential entry point for attackers. Regularly audit open ports and close any that aren't needed.