Cisco Cisco 5520 Wireless Controller 기술 참조

5500/7500/8500 WLCs have a dedicated Redundancy Port which should be connected back to back 
in order to synchronize the configuration from the Active to the Standby WLC.

Keep-alive packets are sent on the Redundancy Port from the Standby to the Active WLC every 100 
msec (default timer) in order to check the health of the Active WLC.

Both the WLCs in HA setup keep track of gateway reachability. The Active WLC sends an Internet 
Control Message Protocol (ICMP) ping to the gateway using the Management IP address as the 
source, and the Standby WLC sends an ICMP ping to the gateway using the Redundancy 
Management IP address. Both the WLCs send an ICMP ping to the gateway at a one-second interval.

It is highly recommended to have back-to-back direct connectivity between Redundant Ports. 

Here you can see the Redundant Port Connectivity between 5500 WLCs in an HA Setup:

Here you can see the Redundant Port Connectivity between Flex 7500 WLCs in an HA setup:

A direct physical connection between Active and Standby Redundant Ports is highly 
recommended. The distance between the connections can go up to 100 meters at per Ethernet 
cable standards.

WiSM-2 WLCs have a dedicated Redundancy VLAN which is used to synchronize the configuration 
from the Active WLC to the Standby WLC.

A Redundancy VLAN should be a Layer 2 VLAN dedicated for the HA Pairing process. It should 
not be spanned across networks and should not have any Layer 3 SVI interface. No data VLAN 
should be used as a Redundancy VLAN.

Keep-alive packets are sent on Redundancy VLAN from the Standby WLC to the Active WLC every 
100 msec (default timer) in order to check the health of the Active WLC.