Mobility Controller Deployment and High Availability
Deployment fundamentals
Candidates must know controller bring-up order: management IP, licensing, cluster/HA configuration, then AP licensing and VLANs. Understand VRRP-based active-standby HA, cluster deployments with stateful failover, and how APs and clients survive a failover. Know the difference between controller clustering (multiple controllers sharing state) and legacy master/local or primary/backup LMS failover.
HA mechanics to master
In active-standby HA, the standby synchronizes state so APs and clients reconnect quickly; failover time depends on heartbeat and AP fast-failover settings. Cluster deployments distribute APs across members and support hitless failover for APs homed to the failed member. Understand license pooling in clusters and the requirement for consistent software versions.
Traps
Questions often assume HA protects against all failures - it does not protect against split-brain misconfiguration or version mismatch. Another trap: confusing AP fast failover (AP-level) with controller-level HA. Also watch for licensing: standby controllers may need licenses, and cluster licensing behaves differently than standalone.
Worked example
Two controllers in active-standby HA with 200 APs: if the active fails, APs re-home to standby using synchronized state; verify heartbeat VLAN reachability and matching firmware. If firmware differs, failover is blocked - a classic exam distractor.
Operational checks
Validate HA state, sync status, and AP failover behavior during maintenance windows.