Remote Authentication Dial-In User Service (RADIUS) is a system of distributed security that secures remote access to networks and network resources against unauthorized access by using the User Datagram Protocol (UDP).
RADIUS authentication includes two components: an authentication server and client protocols. The server is installed on a machine at the customers site. All user authentication and network service access information is located on the RADIUS server. RADIUS allows for multiple formats that can be suited to an individual customer's requirements. A RADIUS server authenticates users against a UNIX password file, Sun Microsystems Network Information Service (NIS), or in a separately maintained RADIUS database. The RADIUS model works on the client sending authentication requests to the RADIUS server, and acts on acknowledgements sent back by the server.
RADIUS authenticates users through a series of communications between the client and the server.
RADIUS service is not limited to dial-up service. Many firewall vendors support the use of a RADIUS server. Dial-in and VPN users could authenticate using the RADIUS server.
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