For years Cisco has had Wireless LAN Controller (WLC) redundancy for their wireless access points (AP). The setup was simple, simply have an extra WLC as the back up, then configure it the same as the primary. Then in the AP under the “High Availability” tab you can enter the name and IP of the primary, secondary, and tertiary controller. When the primary controller becomes unreachable, the AP will reboot and connect to the secondary controller. This redundancy solution is called N+1, meaning you have an extra controller to handle the load if one of the controllers fail.
This solution works very well, I have it deployed like this in many locations. The challenge with this setup is that you have to purchase licensing for all of your controllers. In an active/standby solution, you need licensing for both of your controllers to handle all of the AP’s, this can be very expensive.
Cisco has come up with an N+1 solution that doesn’t require the expense of purchasing licensing for both primary and secondary controller. In version 7.4 you can purchase the HA-SKU wireless controller. The HA-SKU model is the same controller that you would purchase for the primary controller except it doesn’t require any licenses to work. In my case, I have two Cisco 7510′s, one is the HA-SKU model.
The concept here is to save you money on licensing. You pay for the licensing for the primary WLC, then no licensing for the standby. All AP’s need to connect to the Primary WLC and only connect to the standby when the primary fails. After about 60 days, the HA-SKU standby controller will start sending errors that the AP has been on the controller too long.
There is a N+1 configuration guide. I found that the configuration on the controller is not needed. Simply configure your standby controller to match the wireless configuration on your primary, then add the standby information to the AP (Under High Availability). When the primary controller becomes unreachable, the AP moves to the standby.
In my testing, I used a 1602 AP in Flex Connect mode. The AP took less then 1 minute to move to the secondary controller. The AP did not reboot. Then it took about 1 minute for it to move back to the primary controller.
How has your experience been with N+1 redundancy? Are you using the HA-SKU model and how is it working for you?
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