VRRP N:1 Redundancy Concepts
With N:1 redundancy, you can add one redundant controller for up to three controllers, that is, a redundancy group can consist of four controllers, one of which is a redundant controller.
In an N:1 redundancy group with three primary controllers and one redundant controller, you could consider the redundant controller to consist of three virtual controllers, each of which has a redundancy relationship with a primary controller. You need a unique VRRP ID for each relationship.
Each controller in the redundancy group has a unique controller IP address and a unique local IP address. Local addresses remain constant so a controller can always be identified before and after a failover. If the primary controller fails or is disconnected from the network, an automatic failover to the redundant controller occurs. The redundant controller then takes ownership of the controller IP address of the primary controller and takes over all functions of the primary controller.
After a failover has occurred, there is no longer any redundancy available for the other primary controllers in the redundancy group.
When the primary controller that went down and for which the redundant controller took over comes back up and is stable, a switchback occurs automatically, in which case ownership of the controller IP address is returned to the primary controller that came back up. The redundant controller reassumes its passive position, and redundancy is once again available for all primary controllers in the redundancy group.
Note:When a redundancy failover occurs, wireless clients might experience a service interruption of a few seconds.
Requirements and Restrictions for N:1 Redundancy
These are the requirements and restrictions for N:1 redundancy to function correctly:
- All controllers in a redundancy group must be in the same management VLAN and IP subnet.
- The primary controllers must be stacked.
- If three or four controllers are in the same redundancy group, you must configure one controller as the redundant controller and all other controllers as primary controllers.
- All controllers in the redundancy group must run the same firmware version. If the firmware versions do not match, redundancy does not work.
- The licenses on the redundant controller must match those on the primary controller that has the largest number of licenses. For example, in a redundancy group with two primary controllers, if one primary controller has a license for 10 access points and the other primary controller has a license for 50 access point, the redundant controller must have a license for 50 access points. If the licenses do not match, redundancy does not work.
- For the relationship of each primary controller with the redundant controller, you must configure a unique VRRP ID, also in relation to any other VRRP IDs that might be used for other purposes in the network. You also must configure a unique local controller IP address for each controller in the redundancy group.
- When a failover occurs and the redundant controller takes over for a primary controller, redundancy is no longer available for the other primary controllers in the redundancy group.
Example of an N:1 Redundancy Configuration
The following figure shows an N:1 configuration with three stacked controllers and one redundant controller before a failover has occurred. 
The following figure shows the N:1 settings on the Stacking/Redundancy screen before a failover has occurred. 
The following figure shows an N:1 configuration with three primary controllers and one redundant controller after a failover has occurred: .png)