3Com 4200G 12-Port Configuration Manual page 255

Figure 1-6 AAA implementation procedure for a telnet user
The basic message exchange procedure is as follows:
1) A user sends a login request to the switch acting as a TACACS client, which then sends an
authentication start request to the TACACS server.
2) The TACACS server returns an authentication response, asking for the username. Upon receiving
the response, the TACACS client requests the user for the username.
3) After receiving the username from the user, the TACACS client sends an authentication
continuance message carrying the username.
4) The TACACS server returns an authentication response, asking for the password. Upon receiving
the response, the TACACS client requests the user for the login password.
5) After receiving the password, the TACACS client sends an authentication continuance message
carrying the password to the TACACS server.
6) The TACACS server returns an authentication response, indicating that the user has passed the
authentication.
7) The TACACS client sends a user authorization request to the TACACS server.
8) The TACACS server returns an authorization response, indicating that the user has passed the
authorization.
1-8