Access points stop braodcasting SSIDs

[TrickTrick]

Hi everyone,

I noticed in new deployment 9800-L deployment, that a lot of Access points stop randomly broadcasting SSIDs.

I analyzed the config by using the Wireless Config Analyzer tool, and noticed : 

RF: WLC has 84.6% of APs with failed Interference Profile for 2.4GHz Band

RF: WLC has 25.0% of APs with high channel utilization for 2.4GHz Band

When I reboot those APs (because not all of them are affected), they work normally for about 2 days (more or less than that) and stop broadcasting again.

I'm suspecting the RF interferences as per the warnings displayed in the analyzer tool. Took a look on DCA parameters in the 2.4Ghz band, and changed the "DCA Channel Sensitivity" to high, it was medium by default. The APs are probably too close to each other, I'm trying to understand first if this is the reason why the SSIDs are not broadcasted.

Any suggestions beside of that ? should I enable more channels within the channels list ?

Thank you in advance

[marce1000]

 - You can also specify a syslog server for the APs in the AP Join Profile. This may help to get extra insights.

 Go for a recent release , 17.12.3 is recommended.

 Look at this document : https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9800-series-wireless-controllers/217738-monitor-catalyst-9800-kpis-key-performa.html

Use the links for AP kpis and RF stats for further analysis,

 M.

[TrickTrick]

Strange enough, a lot of APs appear in monitor mode:

AP Name Mac Address Slot Admin State Oper State Width Txpwr Channel Mode

AP100_Basement 70bc.55h7.45cf 0 Enabled Up N/A N/A N/A Monitor

What is more strange, is that some of those are working properly, while those which appear to be normal, are not broadcasting SSIDs

[RxTx]

This is because you have active FRA - check Flexible Radio Assignment Configuration and disable Flexible Radio Assignment and switch back every AP as you want.

[TrickTrick]

Hi,

I'm trying to understand why this is happening ( a lot in monitor mode)
I did btw disable that for 2.4Ghz but still in Monitor Mode

[marce1000]

                   -  FYI  : https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwi74744

  M.

[RxTx]

Probably WLC sw decided ( when FRA was enabled ) that 2.4Ghz it is not usable because of RF interference or another reason from configuration parameters and changed the AP's to ignore 2.4Ghz/monitor mode.

If FRA it is disabled now, every AP that was switched to Monitor or have RF 2.4Ghz disabled will remain in that state until it is manual changed to a desired state - enabled.

[Flavio Miranda]

@TrickTrick 

 No, WLC does not stop advertising SSID because interference. That´s for sure. The problem is something else. It can be bug, most probably it is.

 One situation I can imagine and I went through this in the past is, someone have a wireless network near by and is attacking you. This cause the SSID to desapear from the machines from time to time because the other WLC is sending deauthentication to your clients.

Usually Meraki does that very often depending on how it is configured.  On my case, it was a Meraki gear. But, other vendors, cisco inclusive, have this feature.

One more situation I can come up with is, authentication issue. If the client fail to authanticate too often, the operational system can black list the SSID causing it to desapear from the SSID list.  Keep this also in mind.

[Leo Laohoo]

What models of APs is this behaviour evident?  Are they 2800/3800/4800/1560 or Catalyst 9k APs?

[TrickTrick]

9K APs, 9162

[Leo Laohoo]

Reboot the APs and see if this improves.

If this improves, make it a point to regularly reboot the APs.  

If the switches are Cisco, I have an EnergyWise config that can shut/unshut PoE in a schedule.

[Rich R]

You've not once mentioned what version of software you're using @TrickTrick ?
Refer to TAC recommended link below.

As RxTx and others have said FRA will change AP mode but disabling FRA will not change back the APs which were changed by FRA - you need to change them back manually.

And as Flavio pointed out even if channel utilisation is high the AP should not stop broadcasting the SSID if it is enabled - that is always going to be a software bug.  There have recently been a number of bugs relating to APs incorrectly reporting high channel utilisation too so it is very important to make sure your software is up to date.   Even a containment attack (eg from neighbouring Meraki network) will not stop the APs broadcasting - it will just stop clients from associating.