In a Cisco Unified Wireless network, the LAPs must first discover and join a WLC before they can service wireless clients. However, this presents a question: how did the LAPs find the management IP address of the controller when it is on a different subnet? If you do not tell the LAP where the controller is via DHCP option 43, DNS resolution of "Cisco- capwap-controller.local_domain", or statically configure it, the LAP does not know where in the network to find the management interface of the controller. Reference: https://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless- controllers/119286-lap-notjoin-wlc-tshoot.html