TCP Port Checker

TCP Port Checker

The TCP Port Checker is an online port testing tool that checks whether a specified TCP port can establish a connection through a domain name or IP address. It returns the port status, resolved IP address, connection latency and associated service information. It is useful for server configuration checks, network troubleshooting and port connectivity testing.

What Is TCP Port Checking?

TCP ports are important entry points for network services. Different services commonly use different ports. For example, HTTP typically uses port 80, HTTPS uses port 443, SSH uses port 22 and MySQL commonly uses port 3306. TCP port checking attempts to establish a TCP connection to determine whether the target port is accessible.

Main Features

• Supports TCP port checks using a domain name or IPv4 address
• Supports checking one or multiple specified ports
• Displays whether each port is open or closed
• Displays the IP address resolved from a domain name
• Displays the latency required to establish the TCP connection
• Identifies common network services based on port numbers
• Useful for server and network connectivity troubleshooting

Common TCP Ports

Different network services commonly use standard ports. Checking frequently used ports can quickly determine whether the corresponding service can establish a TCP connection.

Port 80

Port 80 is commonly used for HTTP services and is a standard Web port.

Port 443

Port 443 is commonly used for HTTPS services and encrypted TLS connections to websites.

Port 22

Port 22 is commonly used by SSH for remote login and is widely used for Linux server administration.

Port 3306

Port 3306 is the common default TCP port for MySQL and can be used to check network connectivity to a MySQL service.

Port 3389

Port 3389 is commonly used by the Windows Remote Desktop Protocol (RDP) and can be used to check TCP connectivity to a remote desktop service.

How to Use the TCP Port Checker

1. Enter the domain name or IP address you want to check.
2. Enter one or more TCP ports to test.
3. Click the port check button to start the test.
4. Review the open or closed status, IP address, connection latency and service information for each port.

Understanding the Results

• Open: The target port accepts a TCP connection from the current checking node.
• Closed: A TCP connection could not be established. The service may not be running, the port may not be listening or a network policy may be blocking the connection.
• IP Address: The server IP address used for the connection test after domain resolution.
• Latency: The time required to establish the TCP connection, which can help evaluate network connectivity.
• Service: The common network service associated with the port number.

TCP Port Checking vs. Port Scanning

TCP port checking normally tests specified ports to determine whether TCP connections can be established. Port scanning generally probes a larger range of ports to identify potentially available network services. Their testing scope and typical use cases are different.

Common Use Cases

• Check whether Web server ports 80 and 443 are accessible
• Troubleshoot SSH connectivity problems
• Check network connectivity to MySQL and other database ports
• Verify whether firewall rules affect a specified port
• Troubleshoot network connectivity after server deployment
• Test whether a remote service port is accessible externally

Frequently Asked Questions

Does an open port mean the service is working normally?

Not necessarily. An open port means that a TCP connection can be established from the current checking environment, but it does not prove that the application-layer service is functioning correctly. Further testing with HTTP, SSH, database or other application protocols may be required.

Why Is a Port Closed?

A closed port may indicate that the target service is not running, the service is not listening on that port, a firewall is blocking access, a security group is restricting the connection or the target network is unreachable.

Why Can Domain and IP Checks Produce Different Results?

A domain may resolve to multiple IP addresses and may use a CDN, load balancer or DNS-based traffic distribution. Therefore, the actual IP address used for a domain check may differ from the result obtained by directly checking a specific IP address.

Usage Notes

TCP port check results represent network connectivity between the current checking environment and the target server. If a port appears closed, it should not be assumed that the port is inaccessible from every network. Further investigation may need to consider the server firewall, security groups, listening address and network provider policies.