Cisco 8821 Manual page 92

Wireless Domain Services (WDS)
Wireless Domain Services should be utilized in the Cisco Autonomous Access Point environment, which is also required for
fast secure roaming.
Select one access point to be the primary WDS server and another to be the backup WDS server.
Configure the primary WDS server with the highest priority (e.g. 255) and the backup WDS server with a lower priority (e.g.
254).
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
92