Information About Passive Clients
Passive Clients are wireless devices, such as printers and devices configured using a static IP address. Such clients do no transmit any IP information after associating to an AP. That is why, the controller does not learn their IP address unless they perform the DHCP process.
In the controller, the clients just show up in the Learn IP state and get timed out because of the DHCP policy-timeout.
The Passive Client feature can be enabled on a per WLAN basis. Enabling this feature will change a few default behaviors in order to better accommodate passive clients. These changes include :
No client will ever timeout in the IP_LEARN phase. The controller will keep on waiting to learn their IP address. Note that the idle timeout remains active and will delete the client entry after the timeout period expiry, if the client remains silent all along.
ARP coming from the wired side is broadcasted to all the APs, if the controller does not know the client IP address, to ensure that it reaches the passive client. After this, the controller learns the client IP from the ARP response.
In order to save air time, the controller transforms the ARP broadcast coming from the wired side or from other wireless clients and unicasts them to the wireless client it owns . This is only possible after the controller has learned the MAC-IP binding of its wireless client.
When the controller enables ARP broadcast, the controller does not transform the ARP broadcasts into unicasts but only forwards the broadcast, thereby wasting air time for other clients (with a frame that is not acknowledgeable and therefore less reliable). This pushes the passive client to respond to the ARP request and therefore every other client benefits from learning the MAC-IP binding of the wireless client.