When a new AP is connected to the network it need a way to find a Wireless LAN Controller. It all very well documented but here are some fast hints.
The two useful options are to use DHCP og DNS. What’s best depends…
DHCP is the most flexible option. You might, sometime in the life time of the network need to have some AP to join one controller setup and some to another. It could be because separate solutions exist on the same network. I.E. one WLC setup in Asia and another in Europe. Or that old APs need one WLC and new AP’s another.
Multi type support
The “default” way of setting up DHCP for the access point is to use option 43 with a vendor specific setting. In short it enables the DHCP server to give different options 43 setting to different types of equipment. This can be handy if there something like IP phones in the same subnet or if different models of AP should use different Wireless LAN Controllers. The caveat is that if a new AP model is added the vendor string from that model need to be added to the DHCP server
All type support
If there is no need for assigning different WLC a more simple approach can be made. Simply encoding the IP address(es) of the WLC(s) in HEX and use for options 43 for all DHCP clients in the scope.
Provide the WLC IP address to the AP by registering a DNS A-record with the fixed name CISCO-CAPWAP-CONTROLLER in the DNS domain that is used for the APs. In most common enteprise setup this is very easy to implement. The only what to support multiple WLC setups is to provide different DNS domains for each location. If this is not already done in the enterprise it can be complex to implement.
What to choose
Choose what ever is the most easy for you to manage. If setting DHCP option requires someone else to do it and you can manage DNS your self – Choose DNS and verse versa. The selection is not final. Changing method along the way is no problem
Good to know
The pointer is only used for new APs. Once join a WLC the AP will be informed about all WLC’s in the mobility group. This also means that the pointer can be broke without anyone noticeing in daly use. Only when adding new APs this will show.