Port-Based Authentication Initiation and Message Exchange
During 802.1x authentication, the switch or the client can initiate authentication. If you enable authentication
on a port by using the authentication port-control auto interface configuration command, the switch initiates
authentication when the link state changes from down to up or periodically as long as the port remains up and
unauthenticated. The switch sends an EAP-request/identity frame to the client to request its identity. 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 authentication 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 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.
Note
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. If the authentication fails, authentication can be retried, the port might
be assigned to a VLAN that provides limited services, or network access is not granted.
The specific exchange of EAP frames depends on the authentication method being used.
This figure shows a message exchange initiated by the client when the client uses the One-Time-Password
(OTP) authentication method with a RADIUS server.
Figure 92: Message Exchange
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
1322
Information About 802.1x Port-Based Authentication
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