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AP detects radar on a 5Ghz DFS channel when there is no radar source nearby

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TitleAP detects radar on a 5Ghz DFS channel when there is no radar source nearby
Symptoms
AP detects radar on a 5Ghz DFS channel when there is no radar source nearby
Environment
  • ExtremeWireless
  • DFS
  • Radar
Cause
Radar detection methods are probabilistic, not deterministic, therefore radar signals are very short bursts that are a challenge to detect and are prone to false positive.  Some areas of a building might exhibit no radar detection events, other areas may be plagued with them.  Possible causes are:
  • AP(s) on other channels close to the detecting AP causing unintentional interference that might be detected as radar on another AP.
  • Clients or other valid wireless (non-802.11) devices emit signals that might appear to an AP as radar 
  • Bad 802.11 client drivers emitting signals that look like radar
  • Dense user environments that create transient noise that might be detected as radar where in idle user times, no radar is detected (weekends/nighttime.)
Resolution
Some possible resolutions:
  • Adjust channel plan to avoid interference from nearby channels
  • Bad client drivers should be updated
  • Check for any non 802.11 devices and avoid where possible any frequencies they are known to use.
  • Remove channels known to have false positives from the channel plan
  • Use non-DFS channel if the problem cannot be eliminated.
Additional notes

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