Port 51820 WIREGUARD
Port 51820 is the community default for WireGuard, using UDP.
What is port 51820 used for?
Port 51820 is widely used by WireGuard (UDP), a community convention rather than an IANA assignment. Conventional WireGuard listener port used by wg-quick and most WireGuard setup guides. It sits above the registered range, where most numbers are transient client ports. A fixed high port is worth documenting precisely because tooling often assumes the default.
Ports are the transport-layer address a service listens on. This entry has no TCP assignment: UDP is connectionless, so a client that gets no reply may be hitting either an idle service or a firewall drop. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 51820 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Because this number is not IANA-assigned, a different application may legitimately use it on a machine you do not control. Always identify the actual listening process before deciding that the port belongs to this technology.
Browse all VPN and tunnelling ports
This port number is not assigned by IANA. The entry documents a widely adopted community convention.
Check and block port 51820
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -ulpn 'sport = :51820'Check on Windows
Get-NetUDPEndpoint -LocalPort 51820 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 51820/udpBlock with iptables
sudo iptables -A INPUT -p udp --dport 51820 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 51820 safe to expose?
WireGuard uses modern cryptography and is designed to be exposed, but its public key still must be protected and peers restricted. Keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Where port 51820 is usually used
Most traffic on port 51820 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Remote workers establishing an encrypted tunnel to the office or cloud network.
- Site-to-site links between networks that must not expose internal services.
- Road-warrior clients roaming between Wi-Fi and mobile networks.
Inspect WireGuard state
Check interface state and the latest handshake rather than probing the UDP port.
wg showCommon problems with port 51820
No reply from the service
Because UDP has no handshake, a missing reply can mean the service is idle, the packet was dropped, or the client sent it to the wrong interface. Check the listener locally before blaming the network.
Port already in use
Find the process holding the port with sudo ss -ulpn 'sport = :51820' or sudo lsof -i :51820. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 51820 at a glance
| Port number | 51820 |
|---|---|
| Service name | WireGuard |
| Transport protocol | UDP |
| Category | VPN and tunnelling |
| Range | High port (10001–65535) |
| Risk level | Standard/Low |
| Reference | Community convention (not IANA-assigned) |
| Registry description | Conventional WireGuard listener port used by wg-quick and most WireGuard setup guides |
| Source | Community convention |
Frequently asked questions
What is port 51820 used for?
Port 51820 (WIREGUARD) uses UDP. Conventional WireGuard listener port used by wg-quick and most WireGuard setup guides (community convention, not an IANA assignment).
How do I check if port 51820 is open?
On Linux run `sudo ss -ulpn 'sport = :51820'`. On Windows run `Get-NetUDPEndpoint -LocalPort 51820 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 51820; empty output usually means nothing is bound to it.
How do I block port 51820?
With UFW run `sudo ufw deny 51820/udp`. With iptables run `sudo iptables -A INPUT -p udp --dport 51820 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 51820 safe to expose?
WireGuard uses modern cryptography and is designed to be exposed, but its public key still must be protected and peers restricted. Nevertheless, keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
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Primary data: IANA Service Name and Transport Protocol Port Number Registry. This number is a community convention, not an IANA assignment.
Last reviewed 2026-10-30 · Methodology · About · Privacy