Port 1812 (RADIUS authentication)

RADIUS authentication for Wi-Fi (WPA2/3-Enterprise), VPNs and network devices (FreeRADIUS, NPS).

Registered (user) port, 1024-49151 UDP Directory and authentication Do not expose to the internet

Port 1812 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

What port 1812 is used for

RADIUS authentication for Wi-Fi (WPA2/3-Enterprise), VPNs and network devices (FreeRADIUS, NPS).

Security: should port 1812 be open?

Do not expose to the internet. Allow only your NAS devices, use long shared secrets, and mind the Blast-RADIUS MD5 weakness (2024): require Message-Authenticator or use RADIUS over TLS (RadSec, 2083).

IANA assignment

Service nameProtoDescriptionAssigneeReference

radius TCP RADIUS - RFC 2865

radius UDP RADIUS - RFC 2865

Check what is listening on port 1812

Linux: UDP 1812

sudo ss -ulnp 'sport = :1812'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1812

Windows (Command Prompt)

netstat -ano | findstr :1812

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 1812

Test it from outside

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 1812

Block port 1812 in the firewall

ufw

sudo ufw deny 1812/udp

iptables

sudo iptables -A INPUT -p udp --dport 1812 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1812 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1812' -Direction Inbound -Protocol UDP -LocalPort 1812 -Action Block

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.