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9-4
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 9 Configuring IEEE 802.1x Port-Based Authentication
Understanding IEEE 802.1x Port-Based Authentication
Figure 9-2 Message Exchange
Ports in Authorized and Unauthorized States
During IEEE 802.1x authentication, depending on the switch port state, the switch can grant a client
access to the network. The port starts in the unauthorized state. While in this state, the port that is not
configured as a voice VLAN port disallows all ingress and egress traffic except for IEEE 802.1x
authentication, CDP, and STP packets. When a client is successfully authenticated, the port changes to
the authorized state, allowing all traffic for the client to flow normally. If the port is configured as a voice
VLAN port, the port allows VoIP traffic and IEEE 802.1x protocol packets before the client is
successfully authenticated.
If a client that does not support IEEE 802.1x authentication connects to an unauthorized IEEE 802.1x
port, the switch requests the client’s identity. In this situation, the client does not respond to the request,
the port remains in the unauthorized state, and the client is not granted access to the network.
In contrast, when an IEEE 802.1x-enabled client connects to a port that is not running the IEEE 802.1x
standard, the client initiates the authentication process by sending the EAPOL-start frame. When no
response is received, the client sends the request for a fixed number of times. Because no response is
received, the client begins sending frames as if the port is in the authorized state.
You control the port authorization state by using the dot1x port-control interface configuration
command and these keywords:
• force-authorized—disables IEEE 802.1x authentication and causes the port to transition to the
authorized state without any authentication exchange required. The port sends and receives normal
traffic without IEEE 802.1x-based authentication of the client. This is the default setting.
• force-unauthorized—causes the port to remain in the unauthorized state, ignoring all attempts by
the client to authenticate. The switch cannot provide authentication services to the client through the
interface.
101228
Client
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)