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Catalyst 2928 Switch Software Configuration Guide
OL-23389-01
Chapter 9 Configuring IEEE 802.1x Port-Based Authentication
Understanding IEEE 802.1x Port-Based Authentication
Using IEEE 802.1x Authentication with Guest VLAN
You can configure a guest VLAN for each IEEE 802.1x port on the switch to provide limited services to
clients, such as downloading the IEEE 802.1x client. These clients might be upgrading their system for
IEEE 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 IEEE 802.1x 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 IEEE 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.
To allow network access to clients that failed authentication, configure a restricted VLAN 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 IEEE 802.1x authentication restarts.
Any number of IEEE 802.1x-incapable clients are allowed access when the switch port is moved to the
guest VLAN. If an IEEE 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 IEEE 802.1x ports in single-host or multiple-hosts mode.
You can configure any active VLAN except a voice VLAN as an IEEE 802.1x guest VLAN. The guest
VLAN feature is not supported on trunk ports; it is supported only on access ports.
The switch supports
MAC authentication bypass
. When MAC authentication bypass is enabled on an
IEEE 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
IEEE 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
“Using IEEE 802.1x Authentication with MAC Authentication Bypass” section on page 9-14
.
For more information, see the
“Configuring a Guest VLAN” section on page 9-28
.
