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Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 31 Understanding and Configuring 802.1X Port-Based Authentication
Understanding 802.1X Port-Based Authentication
• Authentication server—Performs the actual authentication of the client. The authentication server
validates the identity of the client and notifies the switch that the client is authorized to access the
LAN and switch services. (The only supported authentication server is the RADIUS authentication
server with EAP extensions; it is available in Cisco Secure Access Control Server version 3.2 and
later.)
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 has changed. 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, which 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 three attempts to start
authentication, the client transmits frames as if the port is in the authorized state. A port in the authorized
state 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 31-2
shows a message exchange that is initiated by the client using the One-Time Password (OTP)
authentication method with an authentication server.
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