10-24
Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter10 Configuring IEEE 802.1x Port-Based Authentication
Understanding IEEE 802.1x Port-Based Authentication
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 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 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.
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.
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 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 “802.1x
Authentication with MAC Authentication Bypass” section on page10-29.
For more information, see the “Configuring a Guest VLAN” section on page10-54.
802.1x Authentication with Restricted VLAN
You can configure a restricted VLAN (also referred to as an authentication failed VLAN) for each802.1x
port on a switch stack or a switch to provide limited services to clients that cannot access the guest
VLAN. These clients are 802.1x-compliant and cannot access another VLAN because they fail the
authentication process. A restricted VLAN allows users without valid credentials in an authentication
server (typically, visitors to an enterprise) to access a limited set of services. The administrator can
control the services available to the restricted VLAN.