How to configure two WLCs to load balance the Lightweight Access Point
Information on the current AP load, which is defined as the number of APs that are joined to the WLC at the time
The AP capacity
The number of wireless clients that are connected to the WLC
The AP then attempts to join the least-loaded WLC, which is the WLC with the greatest available AP capacity. After an AP joins a WLC, the AP learns the IP addresses of the other WLCs in the mobility group from its joined WLC.
Subsequently, the AP sends LWAPP primary discovery requests to each of the WLCs in the mobility group. The WLCs respond with a primary discovery response to the AP. The primary discovery response includes information about the WLC type, total capacity, and current AP load. As long as the WLC has the AP Fallback parameter enabled, the AP can decide to change over to a less-loaded WLC.
Once an AP joins a controller, it only leaves the currently joined controller for a limited number of reasons. For that reason, this load balancing algorithm is only an approximate load balancing algorithm unless you manually define a primary controller for each AP.
Note: Once an access point joins a controller you can assign Primary , Secondary , Tertiary controller . Though it is a manual process it is the best way to Load balance Access Points.
From the GUI, click the Wireless tab in the menu at the top of the window, select the AP from the list of AP's that are registered to the WLC, and click Detail beside the AP.
The All AP's > Details window appears.
In this window, define the primary, secondary, and tertiary controllers.
Note: Define only system names under the primary, secondary, and tertiary controller name fields. Do not enter the IP address or the MAC address of the controller in these fields.
Note: This example does not add a tertiary controller name because there are only two controllers.
Configure the Fallback Feature on WLC
The last step is to configure the Fallback feature on the controller. This feature ensures that the AP switches return to the first WLC when the WLC that comes back on line. Complete these steps:
From the GUI, choose Controller > General.A list of options appears on the General screen.
For the AP Fallback option, choose Enabled from the drop-down menu.
Click Apply.Note: It is sufficient to enable the Fallback feature on the secondary controller alone. But it is recommended to configure it on the primary WLC as well because it can be configured as a secondary controller for other access points.
After you complete these steps, the setup is configured for WLC failover. When the primary controller (WLC-1, in this case) goes down, the APs automatically get registered with the secondary controller (WLC-2). The APs register back to the primary controller when the primary controller comes back on line. AP switching between the primary and secondary controllers also affects the wireless clients associated with these APs.
In controller software release 184.108.40.206, you can configure the wireless network so that the backup controller recognizes a join request from a higher-priority access point and, if necessary, disassociates a lower-priority access point as a means to provide an available port. In order to configure this feature, failover priority must be enabled on the network and assign priorities to the individual access points. By default, all access points are set to priority level 1, which is the lowest priority level.
Note: Be aware that Failover priority takes effect only if there are more association requests after a controller failure than there are available backup controller ports.