Anchor WLC redundancy is achieved through the mobility groups. For redundancy, we can increase the mobility group size, including additional controllers for redundancy.
Does N+1 redundancy works across different mobility groups (Anchor WLCs in different DMZ zones for different internet breakout points for Guest access)?
Does it supports pre-empt (preferred) action when the failed primary Anchor WLC recovers?
For WLC 4.1 version or later, mpings are used for keepalive packets between the foreign and anchor controllers. However, there is no setting to set the order of preferred Anchor controllers.