Authentication Initiation And Message Exchange - Cisco 6500 Series Software Configuration Manual

Chapter 25 Configuring IEEE 802.1X Port-Based Authentication

Authentication Initiation and Message Exchange

The switch or the client can initiate authentication. If you enable authentication on a port by using the
dot1x port-control auto interface configuration command, the switch must initiate authentication when
it determines that the port link state transitions from down to up. The switch then sends an
EAP-request/identity frame to the client to request its identity (typically, the switch sends an initial
identity/request frame followed by one or more requests for authentication information). When the client
receives the frame, it responds with an EAP-response/identity frame.
If the client does not receive an EAP-request/identity frame from the switch during bootup, the client
can initiate authentication by sending an EAPOL-start frame, which prompts the switch to request the
client's identity.
Note If 802.1X is not enabled or supported on the network access device, any EAPOL frames from the client
are dropped. If the client does not receive an EAP-request/identity frame after three attempts to start
authentication, the client transmits frames as if the port is in the authorized state. A port in the authorized
state effectively means that the client has been successfully authenticated. For more information, see the
"Ports in Authorized and Unauthorized States" section on page
When the client supplies its identity, the switch begins its role as the intermediary, passing EAP frames
between the client and the authentication server until authentication succeeds or fails. If the
authentication succeeds, the switch port becomes authorized. For more information, see the
Authorized and Unauthorized States" section on page
The specific exchange of EAP frames depends on the authentication method being used.
shows a message exchange initiated by the client using the One-Time-Password (OTP) authentication
method with a RADIUS server.
Figure 25-2 Message Exchange
Client
78-14099-04
Catalyst switch
Cisco Router
EAPOL-Start
EAP-Request/Identity
EAP-Response/Identity
EAP-Request/OTP
EAP-Response/OTP
EAP-Success
Port Authorized
EAPOL-Logoff
Port Unauthorized
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
Understanding 802.1X Port-Based Authentication
25-4.
or
RADIUS Access-Request
RADIUS Access-Challenge
RADIUS Access-Request
RADIUS Access-Accept
25-4.
Authentication
server
(RADIUS)
"Ports in
Figure 25-2
25-3