Designing High Availability
Once an AP has discovered, selected, and joined a controller, it must stay joined to that controller to remain functional. Now consider that a single controller might support as many as 1000 or even 6000 APs—enough to cover a very large building or an entire enterprise. If something ever causes the controller to fail, a large number of APs would also fail. In the worst case, where a single controller carries the enterprise, the entire wireless network would become unavailable. That might be catastrophic.
Fortunately, Cisco APs can discover multiple controllers—not just the one that it chooses to join. Figure 11-2 shows this scenario. If the joined controller becomes unavailable, the AP can simply select the next least-loaded ...
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