3Com Switch 7750 Configuration Guide

510 CHAPTER 49: AAA & RADIUS & HWTACACS CONFIGURATION
The basic message exchange procedure of RADIUS is as follows:
1 The user enters the user name and password.
2 The RADIUS client receives the user name and password, and then sends an
authentication request (Access-Request) to the RADIUS server.
3 The RADIUS server compares the received user information with that in the Users
database to authenticate the user. If the authentication succeeds, the RADIUS
server sends back an authentication response (Access-Accept), which contains the
information of user’s rights, to the RADIUS client. If the authentication fails, it
returns an Access-Reject response.
4 The RADIUS client accepts or denies the user depending on the received
authentication result. If it accepts the user, the RADIUS client sends a
start-accounting request (Accounting-Request, with the Status-Type filed set to
“start”) to the RADIUS server.
5 The RADIUS server returns a start-accounting response (Accounting-Response).
6 The user starts to access the resources.
7 The RADIUS client sends a stop-accounting request (Accounting-Request, with the
Status-Type field set to “stop”) to the RADIUS server.
8 The RADIUS server returns a stop-accounting response (Accounting-Response).
9 The resource access of the user is ended.
RADIUS packet structure
RADIUS uses UDP to transmit messages. It ensures the correct message exchange
between RADIUS server and client through the following mechanisms: timer
management, retransmission, and backup server. Figure 129 depicts the structure
of the RADIUS packets.