When an access point is trying to discover a controller using DNS, it performs a lookup for the domain "CISCO-CAPWAP-CONTROLLER.localdomain". This is because the access point needs to resolve the controller's IP address to establish a connection using the Control and Provisioning of Wireless Access Points (CAPWAP) protocol. The DNS server should have a record that maps the "CISCO-CAPWAP-CONTROLLER" name to the IP addresses of one or more controllers in the network123. References: * Cisco Community: WLC CAPWAP join with DNS name resolution option1. * Cisco Wireless Controller Configuration Guide, Release 8.62. * Cisco Community: IP DNS query3.