TCP Lookup

TCP Lookup & Port Checker - Test TCP Connection and Open Ports

Our TCP Lookup tool helps you check TCP connectivity, test open ports, and verify server availability instantly. Whether you’re troubleshooting network issues, testing port forwarding, or ensuring your web and email services are reachable, this online TCP Port Checker makes it quick and accurate.

What Is TCP Lookup or Port Checker?

A TCP Lookup (also called a TCP Port Test) is a simple way to verify whether a specific port on a remote server or IP address is open and accepting connections. It helps determine if your system or service is accessible and working as expected.

For example, you can test:

• Port 80 for web servers (HTTP)
• Port 443 for secure web servers (HTTPS)
• Port 25 for email servers (SMTP)
• Port 22 for SSH access

This tool is perfect for network administrators, developers, and security engineers who need to confirm that TCP connections are functioning properly.

How Our TCP Lookup Tool Works

1. Enter the IP address or hostname of your target server.
2. Specify the port number you want to check (e.g., 80, 443, 25).
3. Click “Test TCP” to start the connection test.
4. The tool will perform a TCP handshake and report whether the connection succeeds or fails.

Example Inputs:

8.8.8.8:53

https://example.com:443

smtp.gmail.com:25

Understanding the TCP Handshake

TCP uses a three-step handshake to establish reliable communication between two devices:

1. SYN: The client sends a connection request to the server.
2. SYN-ACK: The server acknowledges the request.
3. ACK: The client confirms the acknowledgment, connection established!

If any step fails, the connection can’t be completed, usually due to firewalls, routing issues, or misconfigured services.

Why Use a TCP Port Checker?

Our TCP Lookup tool provides a fast, reliable way to test ports and connections. Here’s what you can do with it:

• Check Port Availability: Instantly see if a specific port is open or closed.
• Verify Service Status: Confirm your website, email, or FTP services are reachable.
• Test Port Forwarding: Ensure your router or firewall rules are configured correctly.
• Troubleshoot Connectivity Issues: Identify blocked or timed-out ports.
• Improve Network Security: Detect unnecessary or exposed ports that may pose risks.

Common TCP Ports You Can Test

Troubleshooting TCP Connection Errors

If your TCP test fails, try the following steps:

• Make sure the target server is online and reachable.
• Check for firewall or router rules blocking the port.
• Confirm that your service is listening on the specified port.
• Use Ping or Traceroute tools to detect network-level problems.
• Verify that the port isn’t already in use by another application.

TCP vs. UDP: What’s the Difference?

While TCP ensures reliable, ordered data transfer through its handshake process, UDP (User Datagram Protocol) is faster but doesn’t guarantee delivery.

• Use TCP for applications like web, email, or file transfers.
• Use UDP for streaming, gaming, or DNS queries.

Start Testing Your TCP Ports Today

TCP testing is essential for maintaining network reliability, diagnosing connection problems, and keeping your systems secure.

Use our TCP Lookup & Port Checker now to test your connection, find open ports, and ensure your network is running smoothly.