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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
—
Release 8.1
78-15486-01
Chapter 31 Configuring 802.1x Authentication
Understanding How 802.1x Authentication Works
Authentication Initiation and Message Exchange
The switch or the host can initiate authentication. If you enable authentication on a port by using the set
port dot1x mod/port port-control auto command, the switch must initiate authentication when it
determines that the port link state transitions from down to up. The switch sends an EAP-request/identity
frame to the host to request its identity (typically, the switch sends an initial identity/request frame that
is followed by one or more requests for authentication information). When the host receives the frame,
it sends an EAP-response/identity frame.
However, if during bootup, the host does not receive an EAP-request/identity frame from the switch, the
host can initiate authentication by sending an EAPOL-start frame, which prompts the switch to request
the host’s identity.
Note
If 802.1x is not enabled or supported on the network access device, any EAPOL frames from the host
are dropped. If the host does not receive an EAP-request/identity frame after three attempts to start
authentication, the host transmits frames as if the port is in the authorized state. A port that is in the
authorized state means that the host has been successfully authenticated. For more information, see the
“Ports in Authorized and Unauthorized States” section on page 31-4
.
When the host supplies its identity, the switch acts as the intermediary, passing EAP frames between the
host 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 31-4
.
The specific exchange of EAP frames depends on the authentication method that is being used.
Figure 31-2
shows a message exchange that is initiated by the host using the One-Time-Password (OTP)
authentication method with a RADIUS server.
Figure 31-2 Message Exchange
Supplicant
Catalyst switch
Port Authorized
Port Unauthorized
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
EAPOL-Logoff
Authentication
server
(RADIUS)
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