What is the role of a secondary wireless LAN controller?

A secondary wireless LAN controller (WLC) acts as a backup in a high-availability setup. Its primary role is to take over and register Lightweight Access Points (LAPs) if the primary WLC becomes unavailable due to a failure. This ensures continued wireless service without significant downtime. The other options are incorrect: While WLCs facilitate roaming, a secondary WLC's specific role isn't to enable roaming between itself and the primary but to provide redundancy for the primary's functions. WLCs typically operate in an active/standby or N+1 redundancy model. The secondary WLC doesn't share the LAP registration load concurrently with the primary; it only takes over if the primary fails. Similarly, the secondary WLC doesn't share the LAPs' traffic load with the primary in an active/standby configuration. The active WLC handles the traffic, and the secondary only assumes this role upon failover.