Cisco 8821

Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
101
Power Management
Proxy ARP can optimize idle battery life, by answering any ARP requests on behalf of the phone.
To enable Proxy ARP, set Client ARP Caching to Enable.
Also ensure that Forward ARP Requests to Radio Interfaces When Not All Client IP Addresses Are Known is checked.