How to configure the same SSID for multiple VLANs on WLCs
Unlike a distributed architecture with autonomous APs, a centralized architecture with the Lightweight Access Point Protocol (LWAPP) does not allow the wireless LAN (WLAN) service set identifier (SSID) to be mapped to multiple virtual LANs (VLANs). This is because the configuration in the WLAN controller (WLC) applies to all the access points (APs) that are registered to it. But, if there is another controller, the WLAN can be mapped to a different VLAN.
When there are two controllers, both of the controllers cannot be the primary. Only one controller can be the primary, and the other must be the secondary. As far as the AP that registers to the controller is concerned, it is recommended to set the switchport that the AP connects to as the access port, because the client VLAN is not related to the VLAN on which the AP sits.
When the primary controller changes on the AP, the AP automatically reboots and joins that controller, given these configurations:
The mobility domain is configured identically on both of the controllers.
The mobility peers are configured on each of the controllers.
The virtual interface IP is identical on both of the controllers.
With the mobility configured, each controller is aware of the controllers that are available for the AP to join. The controllers communicate this information amongst themselves, even before the AP decides to change controllers. The specification of the name on the AP merely triggers that movement to a new controller.