How does a WLC achieve stateful switchover for APs and clients?
How does a WLC achieve stateful switchover for APs and clients?
A WLC (Wireless LAN Controller) achieves stateful switchover for APs (Access Points) and clients by the active WLC establishing a CAPWAP (Control and Provisioning of Wireless Access Points) tunnel with the AP. The standby WLC maintains a synchronized copy of the AP and client databases from the active WLC. This ensures that in the event of a failure, the standby WLC has all the necessary information to take over seamlessly without requiring APs to re-establish connections or databases to be rebuilt, minimizing disruption in service.
Confirmed
In HA mode, WLCs use the same AP-manager interface for communication with the APs. This ensures seamless failover and allows the standby controller to use the existing capwap tunnel to communicate with the AP. The AP database info is sync'd over the physical connection between the two devices.
from OCG p.525 Each AP learns of the HA pair during a CAPWAP discovery phase and then builds a CAPWAP tunnel to the active controller. The active unit keeps CAPWAP tunnels, AP states, client states, configurations, and image files all in sync with the hot standby unit. The active controller also synchronizes the state of each associated client that is in the RUN state with the hot standby controller. If the active controller fails, the standby will already have the current state information for each AP and client, making the failover process transparent to the end users.
I'ts B...
I'll go with B
The new High Availability (HA) feature (that is, AP SSO) set within the Cisco Unified Wireless Network software release version 8.0 and above allows the access point (AP) to establish a CAPWAP tunnel with the Active WLC and share a mirror copy of the AP database with the Standby WLC. The APs do not go into the Discovery state when the Active WLC fails and the Standby WLC takes over the network as the Active WLC.
B is correct
B is correct
During stateful switchover, the active and standby WLCs synchronize critical information, such as AP and client databases, to ensure a seamless transition. This synchronization helps in maintaining the established connections during failover events.
Does AP database includes client database?
B allows the access point (AP) to establish a CAPWAP tunnel with the Active WLC and share a mirror copy of the AP database with the Standby WLC https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-7/High_Availability_DG.html#pgfId-202764