Refer to the exhibit.

The Device Management (View by Device) page lists all devices and lets you manage the devices' access to the network. For each device, you can allow or deny network access.

When you select the Deny option, a message advises you that any certificates associated with it will be revoked. The device cannot be re-enrolled as long as access is denied. To re-enroll the device, you must use this field to allow access again.

References: http://www.arubanetworks.com/techdocs/ClearPass/6.6/Guest/Content/Onboard/DeviceManagement.htm