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Hard to come back to DFS channel

  • 1 June 2020
  • 6 replies
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I have an AP122 allowed to work on DFS channels.

Usually AP selects channel 136 because it is the only one transmitting on that channel (0 interferences from other APs nearby).

However, after detecting radar signals AP does not come back to that DFS channel after several days or even weeks. Logs keep saying this: “ah_dcd: wifi: [DFS-dcost] wifi1: Invalid channel 136” after radar signal disappears.

I thought that once radar signals are not detected anymore, AP would come back in a matter of minuter/hours.

 

Any hint?

Regards

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Best answer by john_kern 4 November 2020, 17:06

Coming back to this thread, I’ve since stopped using DFS channels, as I’ve been told by GTAC that APs do not perform background scans while on a DFS channel. This means no radio auto power adjustments, or rrm channel changes.

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Userlevel 2

Until the next scheduled ACSP scan happens, it's the expected design that the AP will not switch back to the original DFS channel after the radar signal is detected.  But if you enable "Dynamic Frequency Selection > Enable manual channel selection return" in the radio profile (CLI:  radio profile <string> dfs static-channel) and configure a static DFS channel, the AP will try to switch back to the original DFS channel after waiting for 30 minutes following the last channel change caused by the radar signal detection. 

Userlevel 2

@Paul Wang, but unless they’ve changed the default, background scans (acsp) are set for every 10 minutes.

 

@sergi.dupeyou can confirm background scans via cli with “sh int wifi0” or “sh int wifi1” and look for backround scans details (or use “sh int wifi0 | inc bgscan” to filter just the relevant info

 

Following as I’m just starting to use DFS channels and am curious what to look out for.

Userlevel 2

@john_kern - 30 minutes is the NOP (Non occupancy period). If a radar signal is detected on a channel, that channel will not be used for at least 30 minutes.

Userlevel 2

I guess the question would be, is the channel the AP is changing to and staying on acceptable? It won’t specifically go back to the DFS channel it was on unless it was set manually and you check the box for “Enable manual channel selection return”. Otherwise my understanding is after the DFS event (and the 30 minute NOP) the AP will then resume normal ACSP (based on background scans).

I remember using DFS channels in a big area. tons of issues with IoT devices, a lot of manufactures don't support it. eg. roku and fire tv

Userlevel 2

Coming back to this thread, I’ve since stopped using DFS channels, as I’ve been told by GTAC that APs do not perform background scans while on a DFS channel. This means no radio auto power adjustments, or rrm channel changes.

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