U-Star IP

Port Open Check Tool

You set up Remote Desktop, a game server, or home NAS but friends cannot connect — often because the port is closed. Run this port test to see whether your port is truly open.

Common port presets:

3-Line Summary

  • 1Enter an IP and port (80, 443, 3389, etc.) to test reachability in real time.
  • 2Verify port forwarding rules from the external internet's perspective.
  • 3Diagnose inbound firewall blocks with one click.

Ports and Communication Channels

If an IP is a building address, a port is an extension number inside. One computer runs many programs at once; ports from 0 to 65535 tell incoming traffic which service to reach. Web servers usually listen on 80 or 443; Remote Desktop uses 3389.

How Port Forwarding Works

Even if your PC listens on 3389 inside the LAN, external traffic to your public IP:3389 hits the router, which drops the packet unless you map: when public port 3389 arrives, forward to 192.168.0.5:3389. Without that rule, outsiders cannot reach your server.

Common Well-Known Ports

- **21 (FTP):** File transfer - **22 (SSH):** Secure remote shell - **25 (SMTP):** Outbound email - **80 (HTTP):** Unencrypted web - **443 (HTTPS):** Encrypted web (essential) - **1433 (MSSQL) / 3306 (MySQL):** Databases - **3389 (RDP):** Windows Remote Desktop

GOOGLE ADSENSE

Frequently Asked Questions (FAQ)

Windows Defender Firewall or other OS firewalls may block inbound traffic. Add an inbound rule allowing your port and program under Windows Firewall advanced settings.
Mass scanning someone else's server without permission may trigger blacklists. Checking your own specific port occasionally for debugging is legitimate network troubleshooting.

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