topic Background scans not running in Aerohive Migrated Content

Background scans not running

itmanager2 — Tue, 14 Jan 2020 09:24:51 GMT

Hi,

I have my background scans configured to run every 10 minutes without exception (everything unticked under "skip background when...).

When I do a "show acsp channel-info detail" the WAP still hasn't completed scanning of all channels - particularly on wifi1, but sometimes on both wifi0 and wifi1.

I'm running AP245X and AP250 on 8.4r10 and 8.4r11.

Any ideas ?

Cheers

Ian

Re: Background scans not running

bpowers — Tue, 14 Jan 2020 21:16:54 GMT

What channel is the AP on? If an APs 5 GHz radio is on a DFS channel cannot leave said channel to do background scans as it would be in violation if it were to leave and miss a radar hit.

Also if you're on legacy HM, and you have the boxes "unticked" you've disabled background scanning during those three options. Note the language of the checkbox "Enable background scanning when there is traffic with voice priority". So when the box is checked, the AP will do background scans even if voice priority traffic is present.

Re: Background scans not running

w1f1n00b — Wed, 15 Jan 2020 01:29:34 GMT

Any more info on the DFS issue? It's my understanding that background scanning is an integral part of the APs operation. Does this mean that they will never perform background scans when using DFS channels?

Re: Background scans not running

bpowers — Wed, 15 Jan 2020 03:24:54 GMT

I feel like I had a good document detailing this out but cannot seem to locate it. Here is a snippet from the Cisco RRM Guide about how they handle it.

NDP and DFS

NDP is transmitted on all regulatory channels selected under monitor channels list. However DFS channels represent a special case as in order to transmit on a DFSchannel a station must either be a Master, or in the case of the client - associated directly to a legal Master. In order to become a Master, an AP must monitor the channel for 60 seconds to verify that no Radar is present before transmitting on that channel. A client hearing a beacon on a DFS channel can infer that the channel is owned by a master and transmit to that Master. In order for us to transmit NDP on a channel in the DFS bands that we are not the Master of, we need to first hear either a Beacon or a directed Probe from a client in order to mark that channel as clear, then we can follow up with a transmitted NDP packet within 5 seconds. If there are no other AP's, and there are no clients on other DFS channels, we will never send an NDP on any DFS channel except the one on which we are the Master.

So I may have misspoke on the background scanning. I'll update this again if I find the file/doc I'm looking for...

But either way, DFS and background scanning are a bit different than the non-DFS channels. Regardless of vendor.

Re: Background scans not running

itmanager2 — Wed, 15 Jan 2020 07:46:00 GMT

Hi Brian,

Various channels, as I see it on numerous WAPs including I am sure on ones with non-DFS channels.

The one I am working on at the moment is on channel 100 which is listed in Australia as being Indoors / TPC. Not DFS - but that assumes Aerohive is using the same table I am looking at.

Do you know if there is a command which shows whether a channel in use is "considered" a DFS channel ?

In the original post I did say the wording was "skip background when..." which hinted at but I didn't specifically state - we are on Hivemanager (NG) Virtual Appliance (On Premise) 19.5.1.7-NGVA. I know what you mean about carefully reading the wording. 🙂

Be interested to see what your search finds.

Cheers

Ian