As you may already know, one of the requirements to use all the available wifi US 5GHz channels is supporting DFS on the Access Point; when DFS is enabled, it scans active and inactive 5Ghz channels for a minute at a time to ensure that there is no conflict with any radar signals which may also operate in this spectrum. If radar pulses are detected, that channel is black-holed for at least 30 minutes.

DFS detects radar operating close to our site; however, I'm curious whether there is a list of DFS black-holed channels in the WLC... so far, I've been turning up a big zero... all I can find are SNMP traps from the controller...

Channel changed for Base Radio MAC: de:ad:be:ef:00:00 on 802.11a radio. 
Old Channel: 56. New Channel: 161. Why: Radar. Energy before/after
change: 0/0. Noise before/after change: 0/0. Interference before/after change: 0/0.

Is there a way to find the current list of DFS-blackholed channels via the console or GUI? If so, how?

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Commented Aug 11, 2017 at 1:38
  • OK. I'm just check on all the questions with answers that have not accepted any. There have been dozens that have now accepted, and I believe you have been the recipient of some of those.
    – Ron Maupin
    Commented Aug 11, 2017 at 13:55
  • I have a WLC and his answer only works with autonomous mode APs. That's why I never accepted the answer Commented Aug 11, 2017 at 23:03

1 Answer 1


Although this seems to be an AP-based rather than WLC-based command, it would appear you can get the info you want from the AP CLI through

show controller dot11radio1

The output includes a section called "DFS Blocked Frequencies" which should be what you're looking for.

See: http://www.cisco.com/c/en/us/td/docs/wireless/access_point/12-4-25d-JA/Configuration/guide/cg_12_4_25d_JA/scg12-4-25d-JA-chap6-radio.html

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