Controllerless Networks

Hi,

I have a 203H which does not honor the manual channel setting. It is set to 116E, but has been on 36E, 52E and 100E this morning. Rebooting it causes it to go to 116E but it then starts jumping to other channels. Currently it's back on 116E, but the transmission power is 4 dB (see screenshot) which effectively means that no clients will attach to it. The RF settings are 12 min and 18 max.

The 203H is part of a small residential virtual controller network consisting of two IAP-205s, one 203R, and the troublesome 203H, all running 6.5.4.8. All APs except the 203R are connected by ethernet to a "dumb" switch, while the 203R is connected by mesh to one of the 205s. The 5GHz spectrum is fairly clean, with only a handful of interfering APs mostly in the lower frequencies (36, 52 and 104).

I have set the channels of all APs manually because I wanted to direct the 203R to mesh with the nearest IAP-205 only. Because the 203R doesn't support channels over 140, I set the more distant IAP-205 to 149E to "hide" it from the 203R. The mesh portal IAP-205 can then be on any channel that is supported by the 203R, up to and including 116E. I have also taken the 203H out of the mesh by setting its flexible radio to 5 GHz only.

Under what circumstances can an AP override the manual channel setting? And what would cause it to go down to 4 dB power?

BR,

--Martin

SSH into that specific access point and type "show ap arm history".  That will tell you the reason why the channels are changing:  https://www.arubanetworks.com/techdocs/Instant_83_WebHelp/Web_Help_Index.htm#Instant_CLI/show_ap_arm_%20bandwidth_management.htm?Highlight=arm%20history

Thank you for the tip! Here's what I get:

203h-lvrm# show ap arm history

Interface :wifi0

ARM History

-----------

Time of Change       Old Channel  New Channel  Old Power  New Power  Reason  Result

--------------       -----------  -----------  ---------  ---------  ------  ------

2018-08-16 12:38:55  116E         36E          15         15         R       Configured

2018-08-16 12:38:06  116E         100E         15         15         R       Configured

2018-08-16 12:32:29  116E         36E          0          0          R       Configured

Interface :wifi1

I: Interference, R: Radar detection, N: Noise exceeded, Q: Bad Channel Quality E: Error threshold exceeded, INV: Invalid Channel, G: Rogue AP Containment, M: Empty Channel, P+: Increase Power, P-: Decrease Power, 40INT: 40MHZ intol detected on 2.4G, NO40INT: 40MHz intol cleared on 2.4G, OFF: Turn off Radio, ON: Turn on Radio, D: Dynamic Bandwidth Switch, I*: CCA Interference

203h-lvrm#

So... radar detection? Really? On multiple channels? Radar interference is not supposed to be a problem here and I've never seen this error before. Also, running the same command on the other APs shows nothing of interest. The APs involved in the mesh report P+ and P- events, the remaining IAP-205 reports nothing at all.

I am beginning to lean towards the idea that the 203H is flaky. That would also explain some previous behavior.

Cheers,

--Martin

Oh, I could add that I got the 203H to go from 4 dB to 15 dB by manually changing the transmit power level. Initially I only set the channel and left the power level at 0. In the other APs, this results in ARM managing the power level.

I now went and changed the transmit power level manually on the 203H to 15 dB for a moment (see attached screen shot), and the clients now think it has a decent enough RSSI to connect to. The channel is still randomly selected.

Cheers,

--Martin

The radar detection could be false, as to pass regulatory, radar detection on DFS channels typically needs to be very sensitive.  False positives are generally less on 40 and 20mhz channels.

Setting the transmit power  at the lowest power would end up setting it at the lowest EIRP, which could be 4 for that access point on that channel.

I've let the APs sit for the day. The 203H has received a couple more radar events that cause it to change channel. The APs that are in the wireless mesh report occasional P+ and P- events while the non-meshed IAP-205 reports nothing. I understand that the radar detection needs to be sensitive, but this is already affecting the stability of the AP. I'll change it to a non-DFS channel like 36E and keep tracking the situation over the weekend.

About the transmit power: all APs have it set to zero, but the 203H is acting differently from the rest. The other APs go to the minimum power setting when they boot, and then ARM manages the power between min and max. The 203H on the other hand goes to 4 dB when it boots, and stays there. I think what happens is that ARM has no reason to increase the power because there are no clients, but no client is interested in connecting because the RSSI is so low and there are better APs nearby. If I go and change the power manually on the 203H to something else e.g. 15 dB, it sticks there, and if I then change it back to zero it stays at 15 dB. I don't see ARM stepping in to handle the transmit power.

I haven't seen this transmit power behavior before 6.5.4.8, could it be a firmware bug?

Cheers,

--Martin

Setting the per-AP power will fix the power.  Setting the Per-AP channel will fix the channel.  If the AP is on a DFS channel and senses radar, it will attempt to go to another channel that is fixed.  Fixing the channel or power for an AP specifically overrides that parameter with regards to ARM.

You might want to look at the regulatory agency based on your regulatory domain to see if there might be fixed radar (maybe weather) that is in your location, and avoid those channels.

I'll have to defer the radar interference question for now, as there have been no R entries in the log since I changed the channel to 36E. I'll experiment with different DFs and non-DFS channels over the next week or so and see what happens. I also tried to find information about local radars but found nothing of interest yet.

I investigated the power issue further and my hypothesis is that it's a reporting discrepancy for the 5 GHz band only. Observing the AP signal strength from my laptop, upon boot the AP quickly starts giving a decent signal that is comparable to a manual setting of 12 or 15 dB. The AP also starts picking up clients after a while. The Instant UI however says 4 dB if the flexible radio is set to 5 GHz only, and 5 dB if dual band. It consistently displays this value throughout the UI until I go and change the power manually, and I suspect that an ARM P+/P- event would also cause the value to be updated in the UI. The 2.4 GHz band transmission power seems to be reported OK in all cases, or at least I haven't seen any issues there.

For now, the workaround is to select a non-DFS radio channel, set the power to zero, and try to ignore the 4 dB stated in the access point list.

Correction:

Setting the transmit power to 0 just maintains the last transmit power of that access point:

https://www.arubanetworks.com/techdocs/Instant_83_WebHelp/Web_Help_Index.htm#Instant_UG/CustomizeIAPParams/Configuring%20RadioProfiles.htm?Highlight=radio

I understand what you say, but that's not the behavior I see in practice.

All access points are configured to 0 dB, the minimum is 12 dB and the maximum 18 dB. The 203H reports 4 dB on reboot and sticks there (except clients report a signal strength that is comparable to the other APs, i.e. 12-18 dB). The other three APs go to 12 dB on reboot and often see a couple of ARM power events over the next 10-15 minutes. They have now settled on 18, 15 and 14 dB respectively.

The 203H is still picking up radar events many times a day on the DFS channels. It's stable only on non-DFS channels like 36E and 149E.

If things seem strange to you, please open a TAC case.

http://www.arubanetworks.com/support-services/support-program/contact-support

Hi,

I'm facing exactly same issue with IAP-315. I've 22 APs running 6.5.4.8 firmware. As mvonweis mentioned, access points are stable only on non-DFS channels. Nearest weather radars are using channels 124 and 128.

Please open a TAC case so that you concerns can be investigated.

Morjens @villehai, where did you find those radar frequencies? I'm based in Helsinki and just wanted to check if you have any more information of interest. :-)

Moro! I found this page https://metis.fi/en/2017/01/weather-radars/

and also this datasheet for one radar used in Finland, https://www.vaisala.com/sites/default/files/documents/WEA-MET-WRM200-Datasheet-B210698EN-E-LOW.pdf

Greetings from Tampere!

Thanks, that was a good find. Lots of other interesting information on that site too. :-)

I see the radar events on multiple channels and it may be that the Helsinki-Vantaa airport and the various sea ports (Vuosaari etc.) also cause problems. The 203H is the only AP that detects radar events however, the other APs don't report anything.

Thanks, I'll do that.