Skip to main content
IMMUNITYSEC

Port 51820: WireGuard VPN

Port 51820 is in the Dynamic Ports range (49152 to 65535), which IANA does not assign. It is the listen port used in WireGuard's quick start and in the configuration example in the wg(8) manual, which has made it the conventional WireGuard port. All WireGuard packets are sent over UDP.

51820
UDP

Port Details

Port
51820
Transport
UDP
Service
WireGuard
IANA service name
unassigned
Range
Dynamic port (49152-65535)

Security Exposure

The WireGuard protocol is designed so that a server remains silent unless it receives a valid packet, so a scan of 51820 normally shows nothing. Access to the tunnel depends on peer keys and on each peer's AllowedIPs, which wg(8) defines as the addresses from which incoming traffic for that peer is allowed. Under load, WireGuard answers handshakes with cookie replies to fend off CPU exhaustion.

Hardening

  • +Protect private keys with strict file permissions and rotate keys for peers that leave.
  • +Keep AllowedIPs for each peer as narrow as possible.
  • +Allow UDP 51820 only on the VPN gateway, and filter traffic leaving the tunnel interface by destination.
  • +Keep the kernel or WireGuard implementation updated.

Monitoring

Track the latest handshake time per peer and alert on handshakes from peers that should be inactive. Log traffic leaving the tunnel interface toward internal networks.

Tools for Auditing and Monitoring WireGuard

Tailscale

Free / Commercial
Network Security Tools

Identity-based WireGuard mesh network for teams, with managed coordination and open source clients.

LicenseBSD-3-Clause
PlatformLinux, macOS, Windows, iOS, Android

NetBird

Free / Commercial
Network Security Tools

Open source WireGuard zero trust overlay with SSO, MFA, and a self-hostable management plane.

LicenseBSD-3-Clause AND AGPL-3.0-only
PlatformLinux, macOS, Windows, iOS, Android

Firezone

Free / Commercial
Network Security Tools

WireGuard-based zero trust access platform with policy-based routing and SSO integration.

LicenseApache-2.0 AND Elastic-2.0
PlatformLinux, macOS, Windows, iOS, Android

Related Tool Categories

Network Security Tools→

Zero trust access, secure web gateways, firewalls, and perimeter enforcement platforms.

Frequently Asked Questions

Is WireGuard port 51820 TCP or UDP?→

UDP. The WireGuard protocol sends all packets over UDP.

Do I have to use port 51820 for WireGuard?→

No. ListenPort is optional in the configuration and is chosen randomly if not set; 51820 is the value used in WireGuard's examples.

Why does a port scan show 51820 as closed or filtered?→

WireGuard is designed to stay silent unless it receives a valid packet, so the port looks silent to scanners.

Sources

Port assignments from the IANA Service Name and Transport Protocol Port Number Registry. Services can be configured to run on any port, so traffic on port 51820 is not guaranteed to be WireGuard. Exploited-in-the-wild data from the CISA KEV catalog (CC0).