Controllerless Networks

Frequent Contributor I

AP has a Q Flag - DFS CAC timer running?

Hi All

Was wondering what the Q flag means on an AP105?

I noticed on the dashboard a AP was reported down - checking as to why the AP was down it came back UP again.

Checking its details I saw its Uptime is reported as 47 days with 1 hour less than my other APs (I would expect it have been zero with it being reported as Down.

While checking the details I also noticed the flags - it registreing the Q flag for "DFS CAC timer running".

After a few minutes the Q flag went away and hasn't come back - however I am curious as to what it means?

Aruba Employee

Re: AP has a Q Flag - DFS CAC timer running?

Channel 52-64 and 100-140 are DFS Channels that require the AP to detect radar on the channel and not use the channel if Radar is present.

For it to detect radar, it has to do the following: (simplified procedure)
1. Before operating on the channel, it has to wait for 10 minutes to scan for radar signals on the channel.
2. It has to monitor for Radar signals during the operation on the channel too.
3. If it detects a Radar on the channel it should not be using that channel.

The logs above say, that the AP is doing the initial scan for radar on the DFS channel (as in step 1)

This would mean that AP would initially wait for 10 minutes and would be serving client after the 10 minute period (assuming there are no radar signals)
If there are radar signals on the channel, it would move to another non-radar channel.



Thx to below post

Vinod Kumaar AVM ACMX, ACDX
Principal Network Engineer
Customer Advocacy | Aruba Networks Inc.

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New Contributor

Re: AP has a Q Flag - DFS CAC timer running?

I'm seing alot of DFS CACs running randomly during the day so this explanation probably isn't full.


If I understand the answer, I would expect the AP to run the DFS CAC timer only once when it comes online and not again after. If there was a DFS event on the APs operating channel the AP would vacate that channel and avoid the other affected channels and just continue to operate on a channel that it checked through one of it's previous scans.


However what I'm seing is DFS CACs running randomly during the day and APs just stop operating for 10min on that channel and then switch to another.


May we get a full explanation of the DFS process please?



Guru Elite

Re: AP has a Q Flag - DFS CAC timer running?

All DFS channels are monitored for radar by all APs, all of the time (during their scan cycle), period.  Beyond that, the DFS process above is correct.


You should use the Aruba Utilities app on Android in the Google Play Store to see if you have any DFS channels that have published radar.

*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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