Question about High Availability - 4400

[clybumat1]

We have two old Cisco 4400 WLCs that are due to be retired.  They are setup in high availability mode with the APs configured for a Primary and Secondary controller.

Last night the Primary controller went down so all APs moved to the Secondary.  I'm unable to console into the failed Primary so my first step will be to power cycle it.

Question - If the power cycle fixes the Primary and brings it back online, will the APs leave the Secondary and re-join the Primary? I don't think they will, but I just want to make sure before I do the reboot so there is no disruption of service. 

[Alexey Belousov · Accepted solution]

Hello!

By default on WLC "AP Fallback" is enabled (CONTROLLER->General). In this case, if "Primary controller" is configured on AP, AP will leave Secondary and rejoin to Primary. Check "AP Fallback" configuration on Secondary, I think, it is the same on Primary. 

You can disable or enabe "AP Fallback" on primary via console: config network ap-fallback [disable/enable]. If you disable this configuration then AP will not leave secondary controller. 

[clybumat1]

Thank you.  Upon further research on AP Fallback, I found this.  So since the APs are on the configured secondary controller, they will not leave it if/when the Primary is functional again. 

It is important to note that the AP only performs AP fallback from an unconfigured controller to a configured controller (Primary/Secondary/Tertiary). The AP does not fall back from a secondary controller to the primary controller if it is currently joined to the secondary controller. This is because the secondary controller is a configured controller.

[Alexey Belousov]

Yes, right, I forgot about this important nuance.