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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 9 Configuring IEEE 802.1x Port-Based Authentication
Understanding IEEE 802.1x Port-Based Authentication
• auto—enables IEEE 802.1x authentication and causes the port to begin in the unauthorized state,
allowing only EAPOL frames to be sent and received through the port. The authentication process
begins when the link state of the port transitions from down 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 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 resend 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.
IEEE 802.1x Host Mode
You can configure an IEEE 802.1x port for single-host or for multiple-hosts mode. In single-host mode
(see Figure 9-1 on page 9-2), only one client can be connected to the IEEE 802.1x-enabled switch port.
The switch detects the client by sending an EAPOL frame when the port link state changes to the up
state. If a client leaves or is replaced with another client, the switch changes the port link state to down,
and the port returns to the unauthorized state.
In multiple-hosts mode, you can attach multiple hosts to a single IEEE 802.1x-enabled port. Figure 9-3
on page 9-5 shows IEEE 802.1x port-based authentication in a wireless LAN. In this mode, only one of
the attached clients must be authorized for all clients to be granted network access. If the port becomes
unauthorized (re-authentication fails or an EAPOL-logoff message is received), the switch denies
network access to all of the attached clients. In this topology, the wireless access point is responsible for
authenticating the clients attached to it, and it also acts as a client to the switch.
With the multiple-hosts mode enabled, you can use IEEE 802.1x authentication to authenticate the port
and port security to manage network access for all MAC addresses, including that of the client.
Figure 9-3 Multiple Host Mode Example
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Wireless clients
Access point
Authentication
server
(RADIUS)