What is port 51820 used for?

Port 51820 is the standard UDP port used for WireGuard VPN. It is commonly used by WireGuard, Tailscale, Pivpn, OPNsense, pfSense. Modern, fast, cryptographically audited virtual private network protocol utilizing state-of-the-art cryptography.

How do I check if port 51820 is open?

Enter your public IP or hostname into the scanner tool and click Check. A sub-second raw TCP socket handshake will be initiated from our edge server to port 51820 on your target. If the 3-way handshake finishes with SYN-ACK, the port is OPEN. If an RST packet is returned, the host is reachable but the port is CLOSED. If packets time out without response, the port is FILTERED by an ISP or firewall.

Is port 51820 safe to expose to the public internet?

Port 51820 is generally safe to expose when running standard, patched services with strong authentication. However, always ensure your software is updated and access control policies are strictly enforced.

Why does port 51820 show as closed or filtered?

If port 51820 reports CLOSED or FILTERED, confirm that: 1) Your service is actively running and bound to 0.0.0.0 (not just localhost/127.0.0.1); 2) Your router has a port forwarding rule directing external port 51820 to your machine's local IP; 3) Your operating system firewall (Windows Defender Firewall, ufw, or iptables) allows incoming connections on port 51820.

PORT 51820 UDP Remote Access Low Risk

Port 51820 (WireGuard VPN) Open Check

Modern, fast, cryptographically audited virtual private network protocol utilizing state-of-the-art cryptography.

Live Socket Reachability Probe

Pre-configured for Port 51820

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Port Specifications & Network Behavior

Standard Port Number 51820

Primary Service WireGuard VPN

Transport Protocol UDP

Traffic Classification Remote Access

Residential ISP Status Typically unrestricted by consumer ISPs

Security Exposure Low Suitable for public internet hosting with authentication

Security Advisory: WireGuard VPN (Port 51820)

Silent by design: WireGuard drops unauthenticated packets without any ICMP or response headers, protecting against port scanning.

Port Forwarding & Troubleshooting Checklist

If port 51820 returns CLOSED or FILTERED, work through this verified diagnostic checklist:

1 WireGuard uses UDP, not TCP. Note that raw TCP SYN checks will show filtered because WireGuard only replies to valid cryptographic handshakes over UDP.
2 Verify 'ListenPort = 51820' in /etc/wireguard/wg0.conf.
3 Check router forwards UDP 51820 to the VPN server's static LAN IP.

Verify Host Is Listening Locally

Windows (PowerShell) netstat -ano | findstr :51820

Linux / macOS (Bash) ss -tulpn | grep :51820