Cisco Wireless LAN Controller Concepts

That output is a Rosetta stone for WLC concepts. Every WLC has a set of logical interfaces, each with a role. Understanding them is the difference between a WLC you can configure and one you just stare at.

#The WLC Interface Types#link

#How an AP Joins a WLC#link

Discovery is layered. First the AP gets an IP via DHCP. Then it resolves a special DNS name (`CISCO-CAPWAP-CONTROLLER` + domain name) or uses DHCP option 43 to learn the WLC's IP. Then it sends a CAPWAP Discovery Request — UDP 5246 — and if the WLC responds, they negotiate a join.

If DNS lookup and DHCP option 43 both fail, the AP falls back to broadcasting on the local subnet and trying several other methods (cached WLC addresses, prior join info). This is why an AP shipped to a branch office can be plug-and-play if the DHCP scope includes the WLC IP in option 43.

#Client Roaming#link

Roaming is where WLCs earn their keep. A client walking between APs doesn't want to re-authenticate or re-associate at every step. The WLC maintains a mobility database of clients and coordinates the handoff between APs.

• ▪Layer 2 roaming — client stays on the same subnet, AP-to-AP handoff, fast
• ▪Layer 3 roaming — client moves to a different subnet, WLC tunnels traffic back to the original for continuity
• ▪Intra-controller roaming — same WLC, easy
• ▪Inter-controller roaming — different WLCs, requires mobility tunnel between controllers

#Check Your Understanding#link