check 51820 port open

To check if port 51820 (commonly used by WireGuard VPN) is open, you must test it using UDP, not TCP, as standard port scanners often fail on UDP. Use nmap -sU -p 51820 <IP_ADDRESS in Terminal or specialized online UDP port checkers while your VPN service is running. 

Considerations for Port 51820:

Protocol: WireGuard operates on UDP. Online tools that only scan TCP will show this port as closed or filtered."Silent" Status: If the server is running, it may not respond to scanner packets, often appearing closed even when open (stealth mode).Testing: Test for "UDP open" or "open|filtered" status.Firewall/Router: Ensure port forwarding (51820 UDP) is configured on your router pointing to the internal IP of the WireGuard server, and that firewall rules allow this traffic.Local Check: Run netstat -aon | findstr 51820 (Windows) or ss -luptn | grep 51820 (Linux) to verify if the software is actually