natboxOpen port checker
Your public IP address: checking…
The check connects from our server in Germany to your own IP address only, one port at a time, so it cannot be used to scan anyone else. It tests TCP, not UDP. Your IP address is used for the check and then forgotten: it is not logged or stored.
What the results mean
| Result | Meaning | What to do |
|---|---|---|
| Open | Something on your network accepted the connection. | Nothing, if you meant to open it. If not, find the service and close it. |
| Closed | Your address answered, but nothing listens on that port. | Start the service, or forward the port to the right device. |
| Not reachable | No answer within 3 seconds. | A firewall, your router or your internet provider is dropping it. See below. |
Why your port forwarding does not work
- The service is not running, or it listens only on 127.0.0.1. Check with
ss -ltnon Linux ornetstat -anon Windows. - A firewall blocks it on the device itself: ufw, nftables, Windows Defender Firewall.
- The router forwards to the wrong device, often because the device's local IP changed. Give it a fixed address.
- Your provider uses CGNAT. Many home and mobile connections share one public IPv4 address between customers, so no port forward can ever work. If the address above is not the one your router shows, this is why.
- Your provider blocks the port. Ports 25, 80 and 445 are often blocked on home connections.
Behind CGNAT? Get a public endpoint
If your home connection cannot accept incoming connections, a small server can do it for you. Run a WireGuard tunnel from home to a natbox server and forward its ports to your home, or host the service on the server directly. natbox servers come with their own forwarded IPv4 ports and a routed /80 of IPv6, from $1.00 a month. See what a NAT VPS is.
Port checker questions
How do I check if a port is open?
Start the service that should listen on it, then enter the port above and press Check port. The checker tries to connect to your public IP address from the internet, the same way a visitor would.
Can I check UDP ports, such as WireGuard on 51820?
No. A UDP port that works often sends no answer at all, so an outside check cannot tell it apart from a blocked one. Test UDP services by connecting with their own client.
Can I check another IP address or website?
No. To keep the tool from being used to scan other people, it only checks the address you visit from.
Why does it show the wrong IP address?
If you use a VPN or a proxy, the check sees that address instead of your home connection. Turn the VPN off to test your own line.
More free tools: all tools, WireGuard config generator, IPv6 subnet calculator.