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.
If a client that does not support 802.1X is connected to an unauthorized 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 802.1X-enabled client connects to a port that is not running the 802.1X protocol,
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
If the client is successfully authenticated (receives an Accept frame from the authentication server), the
port state changes to authorized, and all frames from the authenticated client are allowed through the
port. If the authentication fails, the port remains in the unauthorized state, but authentication can be
retried. If the authentication server cannot be reached, the switch can retransmit the request. If no
response is received from the server after the specified number of attempts, authentication fails, and
network access is not granted.
When a client logs off, it sends an EAPOL-logoff message, causing the switch port to transition to the
unauthorized state.
If the link state of a port transitions from up to down, or if an EAPOL-logoff frame is received, the port
returns to the unauthorized state.
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