3Com 2928 User Guide - Page 399

Security and Authentication Mechanisms Information exchanged between a RADIUS client and the RADIUS server is authenticated with a shared key, which is never transmitted over the network. This enhances the information exchange security. In addition, to prevent user passwords from being intercepted on insecure networks, RADIUS encrypts passwords before transmitting them. A RADIUS server supports multiple user authentication methods. Moreover, a RADIUS server can act as the client of another AAA server to provide authentication proxy services. Basic Message Exchange Process of RADIUS Figure 1-2 illustrates the interaction of the host, the RADIUS client, and the RADIUS server. Figure 1-2 Basic message exchange process of RADIUS Host RADIUS client RADIUS server 1) Username and password 2) Access-Request 3) Access-Accept/Reject 4) Accounting-Request (start) 5) Accounting-Response 6) The host accesses the resources 7) Accounting-Request (stop) 8) Accounting-Response 9) Notification of access termination The following is how RADIUS operates: 1) The host initiates a connection request carrying the username and password to the RADIUS client. 2) Having received the username and password, the RADIUS client sends an authentication request (Access-Request) to the RADIUS server, with the user password encrypted by using the Message-Digest 5 (MD5) algorithm and the shared key. 3) The RADIUS server authenticates the username and password. If the authentication succeeds, it sends back an Access-Accept message containing the user's authorization information. If the authentication fails, it returns an Access-Reject message. 4) The RADIUS client permits or denies the user according to the returned authentication result. If it permits the user, it sends a start-accounting request (Accounting-Request) to the RADIUS server. 5) The RADIUS server returns a start-accounting response (Accounting-Response) and starts accounting. 6) The user accesses the network resources. 7) The host requests the RADIUS client to tear down the connection and the RADIUS client sends a stop-accounting request (Accounting-Request) to the RADIUS server. 1-2