WLAN High Availability and WLAN AC Deployment
Domain 6 covers AC high availability: how to keep APs and clients served when an AC or link fails, and how VRRP, dual-link backup and AC virtualization differ.
VRRP hot standby
Two ACs share a VRRP virtual IP. APs discover the VIP, so the master AC handles CAPWAP while the backup monitors it. VRRP alone moves the gateway; WLAN state such as AP sessions and client entries needs HSB synchronization. Without HSB, APs reconnect and clients may reauthenticate.
Dual-link backup
An AP can be configured with a primary and backup AC, giving it an alternative CAPWAP endpoint. The backup must have compatible configuration, licenses and software. Failover can be faster than pure VRRP rediscovery, but it still depends on reachability and consistent service settings.
AC virtualization
Virtualization pools AC resources behind a unified management/control view, improving scale and simplifying configuration. It does not remove the need for network redundancy or license planning.
Worked example: AC1 is 10.1.1.1, AC2 is 10.1.1.2, and the VRRP VIP is 10.1.1.254. DHCP option 43 points APs at the VIP. AC1 fails; AC2 becomes master. If HSB was synchronized, AP and client state are preserved; if not, APs rebuild CAPWAP sessions and clients repeat 802.1X.
Traps: assuming VRRP synchronizes WLAN state; mismatched AC versions or licenses; split-brain when the VRRP link fails; advertising a VIP that APs cannot route to.