Hello,
Cisco Wireless LAN Controller Failover
During installation, we recommend that you connect all lightweight access points to a dedicated controller, and configure each lightweight access point for final operation. This step configures each lightweight access point for a primary, secondary, and tertiary controller and allows it to store the configured mobility group information.
During failover recovery, the following tasks are performed:
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The configured access point attempts to contact the primary, secondary, and tertiary controllers, and then attempts to contact the IP addresses of the other controllers in the mobility group.
•DNS is resolved with controller IP address.
•DHCP servers get the controller IP Addresses (vendor specific option 43 in DHCP offer).
In multiple-controller deployments, if one controller fails, the access points perform the following tasks:
•If the lightweight access point has a primary, secondary, and tertiary controller assigned, it attempts to associate with that controller.
•If the access point has no primary, secondary, or tertiary controllers assigned or if its primary, secondary, or tertiary controllers are unavailable, it attempts to associate with a master controller.
•If the access point finds no master controller, it attempts to contact stored mobility group members by the IP address.
•If the mobility group members are available, and if the lightweight access point has no primary, secondary, and tertiary controllers assigned and there is no master controller active, it attempts to associate with the least-loaded controller to respond to its discovery messages.
When sufficient controllers are deployed, if one controller fails, active access point client sessions are momentarily dropped while the dropped access point associates with another controller, allowing the client device to immediately reassociate and reauthenticate.
To know more about high availability, see http://www.cisco.com/en/US/products/ps6366/products_tech_note09186a00809a3f5d.shtml
