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| 9.8 |  | 802.1X Port-based Authentication |
| 9.8.2 |  | Authentication initiation and message exchange |

The switch or the client can initiate authentication. If authentication is enabled 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. It 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). Upon receipt of the frame, the client responds with an EAP-response/identity frame.

However, if during bootup the client does not receive an EAP-request/identity frame from the switch, the client can initiate authentication by sending an EAPOL-start frame. This prompts the switch to request the client’s identity.

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 a defined number of attempts to start authentication, the client sends 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.

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.

The specific exchange of EAP frames depends on the authentication method being used. Figure shows a message exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server.