I have two 2504 wireless LAN controller that are plugged into the LAN. One as primary and the other as backup.
When I disconnect the primary, the backup must take control of the WIFI access points but no one devices can connect to them.
I waited a few minutes but nothing changed.
Primary controller (before unplugging) :
Backup controller (after unplunning the primary):
When I reconnect the primary, it takes control of the WIFI access points and all devices can connect to them.
Both are connected in trunk, are on the same authorized VLAN and connected in gigabit ethernet.
Here are the configurations I made on the primary controller :
For the last screen I made the same for the secondary controller.
Also both are the same software version.
If you want more precision, i am listening.