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Open Port Checker

Enter a host and port to see whether it would show open from the public internet. Includes presets for Minecraft, Rust, SSH and web ports, and an explanation of why a port often shows closed even when the server itself is running fine.

Target

Host and port

Works for game servers, SSH, web servers — anything listening on a TCP or UDP port.

One port, or a list like 25565, 28015-28016.

Common ports

Result

Enter a host and port, then run the check.

Verify it yourself

Run this from any machine outside your network (a VPS, a phone on mobile data) — running it from the same network as the target proves nothing about internet reachability.

Linux / macOS (nc)

nc -zv play.wespner.eu 25565

Windows (PowerShell)

Test-NetConnection -ComputerName 'play.wespner.eu' -Port 25565

Why ports show closed

The usual suspects

The server process being up doesn't mean the port is reachable from the internet. In rough order of likelihood:

  • Firewall rule blocking it. The OS firewall (ufw, firewalld, iptables/nftables) may not have a rule allowing the port at all. The firewall rule generator builds the exact command to open it.
  • Router NAT / port forwarding. If the server sits behind a home router, the router needs an explicit port-forward rule pointing the external port at the machine's internal IP — otherwise inbound traffic never reaches it.
  • ISP-side CGNAT. Many residential and some mobile ISPs put connections behind Carrier-Grade NAT, so there's no public IP to forward to at all — no router setting fixes this, you'd need a different connection type or a proxy/tunnel.
  • The process isn't actually listening on it, or is bound to 127.0.0.1. A service bound to localhost only accepts connections from the same machine, never from outside — check the bind address in its config, not just that it is "running".
  • Wrong protocol. A game server expecting UDP will never answer a TCP probe (and vice versa). Minecraft Java is TCP; Bedrock, Rust and most other game-server ports are UDP.

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