Cisco Wireless Architectures and Deployment Models
The architecture spectrum
Cisco wireless spans autonomous APs (self-contained, configured individually), the unified/CUWN model (lightweight APs joined to a WLC), FlexConnect (unified control with local data switching), Catalyst 9800 controllers on IOS-XE (including embedded wireless controllers on Catalyst 9000 switches), cloud-managed (Meraki), and SD-Access wireless where the fabric handles client mobility. Know which plane each model splits: in local mode, both control and client data are tunneled to the controller; in FlexConnect, control stays with the WLC while data is switched locally at the AP.
CAPWAP and discovery
Lightweight APs build a CAPWAP tunnel using UDP 5246 for control (secured with DTLS) and UDP 5247 for data. APs discover controllers through DHCP option 43 (Cisco sub-option 241), DNS (CISCO-LWAPP-CONTROLLER.localdomain), local subnet broadcast, or a previously primed controller.
AP modes
Local, FlexConnect, monitor, sniffer, rogue detector, SE-connect (spectrum analysis), and bridge/mesh. Monitor mode is receive-only and used for rogue detection and CleanAir; sniffer mode forwards captured frames to a server.
Traps: DHCP option 43 must carry the correct hex-encoded controller address and the AP must be able to reach it; FlexConnect APs lose local data service if the WLC is unreachable unless the WLAN is configured for local authentication and switching; mesh and bridge modes appear as distractors when the question is really about monitor mode.
Rule of thumb: if the question mentions tunneling client traffic to the controller, the answer is local mode; if it mentions WAN survivability at a branch, the answer is FlexConnect.