You can configure  AP to maintain an ARP cache for associated client devices. Maintaining an ARP cache on AP reduces the traffic load on WLAN by stopping ARP requests for client devices at the AP. Instead of forwarding ARP request to client devices, the AP responds to request on behalf of associated client devices.

When ARP caching is disabled (by default it is) the AP forwards all ARP requests through the radio port to associated clients and the client to which the ARP request is directed responds.When ARP caching is enabled, the AP responds to ARP request for associated clients and does not forward request to clients. When the AP receives an ARP request for an IP address not in the cache, the AP drops the request and does not forward it. In its beacon, AP includes an Information Element (IE) to alert client devices that they can safely ignore broadcast messages to increase battery life.

When a non-cisco device is connected to an AP and is not passing data, the AP may not know the client IP address.In this situation you can enable optional ARP caching. When ARP caching is optional , the AP responds on behalf of the clients with IP address known to the AP, but forwards out its radio port any ARP requests address to unknown clients.When AP learns the IP addresses for all associated clients, it drops ARP requests not directed to its associated clients.

You can enable this by using “dot11 arp-cache [optional] ” CLI command. Use the keyword “optional” if you want to enable this feature optionally.