RADIUS Interface
Remote Authentication Dial-In User Service (RADIUS) is a protocol that manages network access. This protocol provides centralized authentication, authorization, and accounting (AAA) management for users who connect and use a network service.
For authentication and authorization, when a user sends a request to NAS to gain access to a network resource using access credentials, the credentials are passed to the NAS device through the link layer protocol. For example, Point-to-Point Protocol (PPP). Then, the NAS sends a RADIUS Access Request message to the RADIUS server, requesting authorization to grant access through the RADIUS protocol.
For accounting, when NAS grants network access to the user, NAS sends an Accounting Start packet to the RADIUS server to signal the start of the user network access.