Campus lan and Wireless lan solution Design Guide

High availability stateful switchover (HA SSO) 
Cisco wireless LAN controllers support AP stateful switchover and client stateful switchover. These two features 
are collectively referred to as HA SSO. For both simplicity and efficacy, HA SSO is the preferred option for 
providing high availability. Cisco wireless deployments can improve the availability of the wireless network with 
controller recovery times in the sub-second range during a WLAN controller disruption.
The configuration and software upgrades of the primary WLAN controller are automatically synchronized to the 
resilient standby WLAN controller.
N+1 high availability 
You can use the N+1 HA architecture in order to provide redundancy for WLAN controllers within a single site or 
across geographically separate sites with lower overall cost of deployment. It is often deployed along with the 
Cisco FlexConnect architecture in order to provide high availability across data centers for remote branches.
You can use a single backup WLAN controller in order to provide backup for multiple primary WLAN controllers. 
HA SSO functionality is not supported for N+1 HA. When the primary controller fails, the AP CAPWAP state 
machine is restarted. 
With N+1 HA, WLAN controllers are independent of each other and do not share configuration or IP addresses 
on any of their interfaces. Each WLC must be managed separately, can run different hardware, and can be 
deployed in different datacenters across the WAN link.
It is recommended (but not required) that you run the same software version across WLCs used for N+1 HA, in 
order to reduce downtime as the APs establish CAPWAP sessions to the backup controllers. You can configure 
APs with a priority using N+1 HA. APs with high priority on the primary controller always connect first to the 
backup controller, even if they must push out low priority APs. When a primary WLC resumes operation, the APs 
fall back from the backup WLC to the primary WLC automatically, if the AP fallback option is enabled. 

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