DNS: If you have configured your DHCP server to provide both option 006 (DNS server address) and option 015 (domain name) information, the AP can obtain WLC addresses from the DNS server. The process works as follows:
1. The AP gets its IP address from DHCP with options 6 and 15 configured.
2. The AP can obtain the IP address of the DNS server from the DHCP option.
3. The AP uses this information to perform a hostname lookup using CISCO-CAPWAP-CONTROLLER.<localdomain>, which resolves to available WLC management interface IP addresses (IPv4 or IPv6, or both).
4. The AP can then perform a directed message to associate to responsive WLCs.
To prevent all APs from joining a single controller based on a DNS name resolution, the domain name may vary; this is what is done to dispatch APs to different controllers across the enterprise network, based on different domain names that are configured in their respective DNS scopes.