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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter7 Configuring 802.1X Port-Based Authentication
Understanding 802.1X Port-Based Authentication
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 excep t
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 una uthorized 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 ne tw ork .
In contrast, when an 802.1X-enabled client connects to a por t t hat is n ot runn i ng t he 80 2.1X pr otoc ol,
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. Becau se n o re spo nse is r ece ived , 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 802.1X authentication and causes the port to transition to the
authorized state without any authentication exchange required. The port transmits and receives
normal traffic without 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 clien t through the
interface.
•auto—enables 802.1X authentication and causes the port to begin in the unauthorized state,
allowing only EAPOL frames to be sent and received through th e port . T he aut he ntica tio n p roce ss
begins when the link state of the port transitions from dow n to up or when an EAPOL-start frame is
received. The switch requests the identity of the client and begins relaying authentication messages
between the client and the authentication server. Each client attempting to access the network is
uniquely identified by the switch by using the client’s MAC address.
If the client is successfully authenticated (receives an Accept frame from the a uthe nti cation server), the
port state changes to authorized, and all frames from the authenticat ed client are all owed t hrough 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.
Supported Topologies
The 802.1X port-based authentication is supported in two topologies:
•Point-to-point
•Wireless LAN