1-3Figure 1-2 RADIUS server componentsz Users: Stores user information such as the usernames, passwords, applied protocols, and IPaddresses.z Clients: Stores information about RADIUS clients, such as the shared keys and IP addresses.z Dictionary: Stores information about the meanings of RADIUS protocol attributes and their values.Security and Authentication MechanismsInformation exchanged between a RADIUS client and the RADIUS server is authenticated with ashared key, which is never transmitted over the network. This enhances the information exchangesecurity. In addition, to prevent user passwords from being intercepted in non-secure networks,RADIUS encrypts passwords before transmitting them.A RADIUS server supports multiple user authentication methods. Moreover, a RADIUS server can actas the client of another AAA server to provide authentication proxy services.Basic Message Exchange Process of RADIUSFigure 1-3 illustrates the interaction of the host, the RADIUS client, and the RADIUS server.Figure 1-3 Basic message exchange process of RADIUSRADIUS client RADIUS server1) Username and password3) Access-Accept/Reject2) Access-Request4) Accounting-Request (start)5) Accounting-Response7) Accounting-Request (stop)8) Accounting-Response9) Notification of access terminationHost6) The host accesses the resourcesThe following is how RADIUS operates:
