Authentication Initiation And Message Exchange - Cisco Catalyst 3750 Software Configuration Manual

Chapter 8 Configuring 802.1x Port-Based Authentication

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
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.
Note 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 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. For more information, see the
"Ports in Authorized and Unauthorized States" section on page
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. For more information, see the
Authorized and Unauthorized States" section on page
The specific exchange of EAP frames depends on the authentication method being used.
shows a message exchange initiated by the client using the One-Time-Password (OTP) authentication
method with a RADIUS server.
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support EAP within the native frame format. When the switch receives frames from the
authentication server, the server's frame header is removed, leaving the EAP frame, which is then
encapsulated for Ethernet and sent to the client.
The devices that can act as intermediaries include the Catalyst 3750, Catalyst 3550, Catalyst 2970,
Catalyst 2955, Catalyst 2950, Catalyst 2940 switches, or a wireless access point. These devices must
be running software that supports the RADIUS client and 802.1x.
Understanding 802.1x Port-Based Authentication
8-4.
8-4.
Catalyst 3750 Metro Switch Software Configuration Guide
"Ports in
Figure 8-2
8-3