When using N+1 HA make sure the controllers are running V7.4 or later. Pre 7.4 the N+1 HA model requires a permanent AP count license on the backup controller. With Release 7.4 and later, an HA-SKU secondary controller can be used as the backup controller for multiple primary controllers. The overall goal for the addition of N+1 HA with HA-SKU is to reduce the total cost of ownership (TCO) for geographically separate HA deployments across the WAN link.
Keep in mind that Access Point Stateful Switch Over (AP SSO)
functionality is not supported for N+1 HA. The AP Control and Provisioning of
Wireless Access Points (CAPWAP) state machine is restarted when the primary
controller fails. With Release 7.4, the backup
controller for N+1 HA can be an HA-SKU secondary controller. AIR-CT5760-HA-K9
is the HA SKU for the new Cisco 5760 WLC, for example.
an HA WLC, with a different user count to the main controllers, can be used as the HA controller. For example 2 x WISM2 each with 750 AP licenses can be backed up by a WLC5670 which could only support 1000 APs.
The new 5760 WLC
does support N+1 High Availability. If interworking with AireOS
controllers in the same Mobility group, you will
need either a WiSM2 or a CT5508 running 7.3.112.0 release and also in
"Hierarchal Mobility Mode" to form a Mobility group with
IOS-XE based Controllers [3.2.0SE release]. Be aware that in the current
release, when AP's fail between dissimilar WLC Operating Systems (AireOS and
IOS-XE) the AP's do download a new CAPWAP image and reboot; so this failover is
not "sub 45 seconds" but rather 2~3 minutes depending on
download speeds and reboot times of Access Points.
References:
Cisco Catalyst
3850 Series Switches – Q&A
Cisco Catalyst
3850 Switch Deployment Guide
Cisco Unified
Access Technology Overview: Converged Access
Converged
Access Mode for the Cisco 5760 WLC and the Catalyst 3850 Switch
Cisco Wireless
Software Compatibility Matrix - (Converged Access WLC Compatibility Matrix –
Table 6)
Release Notes
for Cisco WLC's and Lightweight Access Points
WLC High
Availability
N+1 High
Availability Deployment Guide
Cisco 5760 WLC
Deployment Guide
Release Notes
for the Cisco 5760 WLC, IOS XE Release 3.2.x SE
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