RADIUS (Remote Authentication Dial-In User Service) is a networking protocol used for centralized authentication, authorization, and accounting (AAA) in network access control. It enables secure user authentication for devices like routers, switches, VPNs, and wireless access points by verifying credentials against a centralized RADIUS server. Once authenticated, the server grants appropriate access and tracks user activity for auditing. Commonly used in enterprise networks, ISPs, and Wi-Fi authentication, RADIUS operates over UDP (ports 1812 for authentication and 1813 for accounting) and supports EAP (Extensible Authentication Protocol) for enhanced security in environments like 802.1X authentication. Learn more: https://en.wikipedia.org/wiki/RADIUS