HP MSR Series Configuration Manual page 18

Basic RADIUS packet exchange process
Figure 3 illustrates the interactions between a user host, the RADIUS client, and the RADIUS server.
Figure 3 Basic RADIUS packet exchange process
RADIUS uses in the following workflow:
1. The host sends a connection request that includes the user's username and password to the
RADIUS client.
2. The RADIUS client sends an authentication request (Access-Request) to the RADIUS server.
The request includes the user's password, which has been processed by the MD5 algorithm
and shared key.
3. The RADIUS server authenticates the username and password. If the authentication succeeds,
the server sends back an Access-Accept packet that contains the user's authorization
information. If the authentication fails, the server returns an Access-Reject packet.
4. The RADIUS client permits or denies the user according to the authentication result. If the result
permits the user, the RADIUS client sends a start-accounting request (Accounting-Request)
packet to the RADIUS server.
5. The RADIUS server returns an acknowledgment (Accounting-Response) packet and starts
accounting.
6. The user accesses the network resources.
7. The host requests the RADIUS client to tear down the connection.
8. The RADIUS client sends a stop-accounting request (Accounting-Request) packet to the
RADIUS server.
9. The RADIUS server returns an acknowledgment (Accounting-Response) and stops accounting
for the user.
10. The RADIUS client notifies the user of the termination.
RADIUS packet format
RADIUS uses UDP to transmit packets. The protocol also uses a series of mechanisms to ensure
smooth packet exchange between the RADIUS server and the client. These mechanisms include the
timer mechanism, the retransmission mechanism, and the backup server mechanism.
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