Cisco Cisco 5520 Wireless Controller 기술 참조

In AP SSO deployment controller running higher permanent count licenses 
should be configured as primary unit. Primary Unit is the WLC, which will take 
the role of Active WLC first time it forms HA pair. Primary Unit sends the lic 
count information to its peer via redundant port.

While booting, standby WLC waits for peer search timer (default 2 minutes) to 
discover the peer. If WLC cannot discover its peer within this time it will 
transition its state to maintenance mode.

Physical Port on 5500/7500/8500 WLC for HA role negotiation, configuration 
sync and redundancy messages between Active and Standby WLC.

Vlan created on Cat6500 Sup for WiSM-2 Redundancy Port that is connected to 
Cat6k backplane to exchange configuration and redundancy messages including 
HA role negotiation between Active and Standby WLC.

A parallel interface to management interface on both the WLC in HA setup. 
Should be in same subnet as management interface. This interface let standby 
WLC interact with infra network and also exchange some redundancy messages 
over infra network between Active and Standby WLC.

This is the WLC that is monitoring active controller in HA pair and ready to take 
over the wireless network in event of Active WLC failure.

In AP SSO deployment controller running lower or equal permanent count lic 
should be configured as secondary unit OR controller with HA SKU UDI (zero 
AP count lic) is shipped default as secondary unit. Secondary Unit is the WLC, 
which will take the role of Standby WLC first time it forms HA pair. Secondary 
unit inherit the lic count information from its peer i.e. Active WLC via redundant 
port.