Cisco Cisco 5520 Wireless Controller 기술 참조

With the new WLC coming up, HA SKU at the time of paring will get the AP Count:

If the new WLC has a higher AP count than the previous, the 90-day counter is reset.

If the new WLC has a lower AP count than the previous, the 90-day counter is not reset.

After switchover to a lower AP count, the WLC offset timer will continue and nagging messages 
will be displayed after time expiry.

The device with HA SKU becomes the Standby WLC the first time it pairs up with an existing Active 
WLC running Evaluation License. Or, any WLC running a permanent license count can be 
configured as the Secondary unit using the CLI configuration provided if it satisfies the requirement 
of minimum permanent license count. This condition is only valid for the 5500 WLC, where a 
minimum of 50 AP Permanent licenses are needed to be converted to Standby. There is no restriction 
for other WLCs such as the WiSM2, 7500, and 8500.

AP-count license information will be pushed from Active to Standby.

In the event of a switchover, the new Active WLC will operate with the license count of the previous 
Active WLC and start the 90-day countdown.

After 90-days, it starts nagging messages. It will not disconnect connected APs.

With new the WLC coming up, HA SKU at the time of paring will get the AP Count:

If the new WLC has a higher AP count than the previous, the 90-day counter is reset.

If the new WLC has a lower AP count than the previous, the 90-day counter is not reset.

After switchover to a lower AP count, the WLC offset timer will continue and nagging messages 
will be displayed after time expiry.

To support High Availability without impacting service, there needs to be support for seamless transition 
of clients and APs from the active controller to the standby controller. Release 7.5 supports Client 
Stateful Switch Over (Client SSO) in Wireless LAN controllers. Client SSO will be supported for clients 
which have already completed the authentication and DHCP phase and have started passing traffic. With 
Client SSO, a client's information is synced to the Standby WLC when the client associates to the WLC 
or the client’s parameters change. Fully authenticated clients, i.e. the ones in Run state, are synced to the 
Standby and thus, client re-association is avoided on switchover making the failover seamless for the 
APs as well as for the clients, resulting in zero client service downtime and no SSID outage.

In controller release 7.3 and 7.4, back-to-back connectivity through redundancy port restrains the 
active and standby controllers to be in different locations. There are two mandatory interfaces for 
redundancy, redundancy port and redundancy management interface. Redundancy port uses 
dedicated physical port eth1 (similar to service port). It is used for all redundancy communication