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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 11 Configuring IEEE 802.1x Port-Based Authentication Understanding IEEE 802.1x Port-Based Authentication
802.1x Authentication with Guest VLAN
You can configure a guest VLAN for each 802.1x port on the switch to provide limited services to
clients, such as downloading the 802.1x client. These clients might be upgrading their system for 802.1x
authentication, and some hosts, such as Windows 98 systems, might not be IEEE 802.1x-capable.
When you enable a guest VLAN on an 802.1x802.1x port, the switch assigns clients to a guest VLAN
when the switch does not receive a response to its EAP request/identity frame or when EAPOL packets
are not sent by the client.
The switch maintains the EAPOL packet history. If an EAPOL packet is detected on the interface during
the lifetime of the link, the switch determines that the device connected to that interface is an
IEEE 802.1x-capable supplicant, and the interface does not change to the guest VLAN state. EAPOL
history is cleared if the interface link status goes down. If no EAPOL packet is detected on the interface,
the interface changes to the guest VLAN state.
If the switch is trying to authorize an 802.1x-capable voice device and the AAA server is unavailable,
the authorization attempt fails, but the detection of the EAPOL packet is saved in the EAPOL history.
When the AAA server becomes available, the switch authorizes the voice device. However, the switch
no longer allows other devices access to the guest VLAN. To prevent this situation, use one of these
command sequences:
• Enter the dot1x guest-vlan supplicant global configuration command to allow access to the guest
VLAN.
• Enter the shutdown interface configuration command followed by the no shutdown interface
configuration command to restart the port.
Use a restricted VLAN to allow clients that failed authentication access to the network by entering the
dot1x auth-fail vlan vlan-id interface configuration command.
If devices send EAPOL packets to the switch during the lifetime of the link, the switch no longer allows
clients that fail authentication access to the guest VLAN.
Note If an EAPOL packet is detected after the interface has changed to the guest VLAN, the interface reverts
to an unauthorized state, and 802.1x authentication restarts.
Any number of 802.1x-incapable clients are allowed access when the switch port is moved to the guest
VLAN. If an 802.1x-capable client joins the same port on which the guest VLAN is configured, the port
is put into the unauthorized state in the user-configured access VLAN, and authentication is restarted.
Guest VLANs are supported on 802.1x ports in single-host or multiple-hosts mode.
You can configure any active VLAN except an RSPAN VLAN, a private VLAN, or a voice VLAN as an
802.1x guest VLAN. The guest VLAN feature is not supported on internal VLANs (routed ports) or
trunk ports; it is supported only on access ports.
The switch supports MAC authentication bypass. When MAC authentication bypass is enabled on
an 802.1x port, the switch can authorize clients based on the client MAC address when IEEE 802.1x
authentication times out while waiting for an EAPOL message exchange. After detecting a client on
an 802.1x port, the switch waits for an Ethernet packet from the client. The switch sends the
authentication server a RADIUS-access/request frame with a username and password based on the MAC
address. If authorization succeeds, the switch grants the client access to the network. If authorization
fails, the switch assigns the port to the guest VLAN if one is specified. For more information, see
the“IEEE 802.1x Authentication with MAC Authentication Bypass” section on page 11-25.
For more information, see the “Configuring a Guest VLAN” section on page 11-51.