User Manual

216
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. 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
I
f 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 authentica
tion, 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.
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 4-11-2” shows a message
exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server.
Figure 4-11-2: EAP Message Exchange
 Ports in Authorized and Unauthorized States
The switch port state determines whether or not the client is granted access to the network. The port starts in the unauthorized
state. While in this state, the port disallows all ingress and egress traffic except for 802.1X protocol packets. When a client is
successfully authenticated, the port transitions to the authorized state, allowing all traffic for the client to flow normally.