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Wireless & Mobility · Intermediate

Dynamic Frequency Selection (DFS)

A requirement that 5 GHz devices detect radar and vacate the channel when radar is present.

Definition

DFS applies to U-NII-2A and U-NII-2C channels where weather and military radar operate. A device must perform a 60-second channel availability check before using a DFS channel, leave within the channel move time when radar is detected, and avoid the channel for 30 minutes (non-occupancy period). DFS events can disrupt clients.

Example

An AP near an airport moves off channel 120 after detecting radar.

Exam tip

Some clients do not support DFS channels; check client capabilities in design.

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