Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 715

Chapter 42 Configuring IEEE 802.1X Port-Based Authentication Understanding 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 42-4. 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 "Ports in Authorized and Unauthorized States" section on page 42-4. The specific exchange of EAP frames depends on the authentication method being used. Figure 42-2 shows a message exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server. Figure 42-2 Client Message Exchange Catalyst switch or Cisco Router Authentication server (RADIUS) EAPOL-Start EAP-Request/Identity EAP-Response/Identity EAP-Request/OTP EAP-Response/OTP EAP-Success RADIUS Access-Request RADIUS Access-Challenge RADIUS Access-Request RADIUS Access-Accept Port Authorized EAPOL-Logoff Port Unauthorized 79551 OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 42-3