RADIUS Authentication
What is Port 1812?
Port 1812 is the standard port for RADIUS (Remote Authentication Dial-In User Service) authentication, defined in RFC 2865. RADIUS is a networking protocol that provides centralized authentication, authorization, and accounting (AAA) for users who connect to network services. RADIUS is used by ISPs for subscriber authentication, enterprises for Wi-Fi (802.1X/WPA-Enterprise), VPN authentication, and network device management access. When a user tries to connect to a RADIUS-protected service, the network access server (NAS) forwards the credentials to the RADIUS server on port 1812. The RADIUS server validates the credentials against its backend (LDAP, SQL, local) and returns an Accept, Reject, or Challenge response. FreeRADIUS is the most widely deployed open-source RADIUS server.
Common Uses
- Wi-Fi WPA-Enterprise (802.1X) authentication
- VPN user authentication
- ISP subscriber access control
- Network device (switch/router) admin authentication
Technical Details
Copy-paste commands to check port 1812 (RADIUS Authentication) from your terminal
Test connectivity
nmap -p 1812 -sU -sV example.com
(echo > /dev/tcp/example.com/1812) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 1812/udp
sudo iptables -A INPUT -p udp --dport 1812 -j ACCEPT
sudo firewall-cmd --permanent --add-port=1812/udp && sudo firewall-cmd --reload
Security Considerations
RADIUS uses shared secrets and MD5 hashing, which have known weaknesses. Use long, random shared secrets and IPSec or TLS to encrypt RADIUS traffic. Consider migrating to RadSec (RADIUS over TLS/DTLS) for modern deployments. Protect the RADIUS server as a critical authentication infrastructure component. Implement logging and monitor for brute force attacks.
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