A. For most vendors, the controller-based APs maintain data and control tunnels with at least two controllers for immediate failover and redundancy.

B. All vendors use the same protocol so that APs will interoperate with WLAN controllers from other vendors.

C. All vendors support at least one L2 or L3 broadcast protocol for controller discovery by controller-based APs.

D. All vendors recommend using L2 (instead of L3) controller discovery and tunneling protocols in large enterprises.

E. Some vendors use proprietary protocols, and some vendors use protocols based on public standards like RFCs.