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PCM reports erroneous WLAN errors

J Vesterdahl
Regular Advisor

PCM reports erroneous WLAN errors

Hi all.

Sorry if this is the wrong forum, but I believe the error is in PCM.

I have some AP530s attached to my network, which is monitored by PCM+ with Mobility Manager.
PCM frequently reports excessive Rx errors on several of these APs although the wireless statistics in the APs web agent reports 0 errors and PCMs own wireless Rx/Tx error report also reports 0 errors.

Does anyone else see this?

PCM+ 2.322 update 7 and 8
Mobility Manager 2.0 update 1
There is always one more bug ...
7 REPLIES
Steve Britt
Respected Contributor

Re: PCM reports erroneous WLAN errors

Hi,

Just to clarify, are you saying that the excessive Rx errors are reported in PCM's Traffic tab or on the Wireless Metrics tab? The numbers on the Traffic tab come from the ifMIB, while those on the Wireless Metrics tab are coming from MIBs that are more wireless-specific.

Regards,

SVB
J Vesterdahl
Regular Advisor

Re: PCM reports erroneous WLAN errors

The errors are reported in the traffic tab and nowhere else.
The wireless metrics report no errors.
There is always one more bug ...
Steve Britt
Respected Contributor

Re: PCM reports erroneous WLAN errors

Hi,

The error counts being reported by traffic are coming from your MIB II ifTable for the ifIndex corresponding to the AP's interfaces. Specifically, the OIDs being referenced are 1.3.6.1.2.1.2.2.1.14 for Rx errors and 1.3.6.1.2.1.2.2.1.20 for Tx errors. If you're monitoring in statistics polling mode PCM is pulling these counts once per minute from the device, and if you're using sFlow these counters are being sent every 20 seconds by the device to PCM (without a request being sent by PCM). So that's where the numbers are coming from.

Unfortunately I will have to defer to someone more knowledgeable about wireless regarding the disparity between errors indicated in the ifTable and the wireless-specific error statistics you're referring to ... but at least now you know where the values are coming from if not why they're being incremented.

Regards,

SVB
J Vesterdahl
Regular Advisor

Re: PCM reports erroneous WLAN errors

Thanks, Steve.

For the record, I get these excessive errors regardless if there are any users connected to the AP or not.

AP firmware WA.02.19

Best regards,
Jens
There is always one more bug ...
J Vesterdahl
Regular Advisor

Re: PCM reports erroneous WLAN errors

Ahem ... looking back in the forum, I see (and remember) that I've asked this before (See thread "Lots of RX errors on AP530" from april '08).

Since then I've added more APs to the network, and I had not changed the traffic parameters on those.


There is always one more bug ...
Steve Britt
Respected Contributor

Re: PCM reports erroneous WLAN errors

Hi,

I consulted with one of our wireless engineers regarding this issue, and here is his multi-part response on the topic. It doesn't really provide any solution to the issue but might give you some peace of mind as to the reasons for the discrepancies.

Regards,

SVB

-----

The PCM Traffic tab (sFlow counters and MIB polling) gets the error count for the physical radio interface whereas the AP530's WebUI and CLI get the error count for the virtual WLAN interface. The WLANs are higher level, so they report different types of errors (and generally much fewer errors) than the physical radios.

The Mobility Manager plugin application for PCM is getting the error count for the radios, but for some reason the radio error table is blank for the Wireless Metrics tab. So there appears to be a bug in MM 2.0 with displaying the proper error count.

In the upcoming release of PCM 3.0 and the MM plugin an error count is being displayed. Unfortunately the numbers still don't match the Traffic numbers because there are only Tx Errors reported through SNMP (which MM displays correctly on the Wireless tab). The sFlow agent on the AP530 is getting some additional internal radio error counters; for Rx it is adding the "miscellaneous" receive error count and the "frame" receive error count into the generic Rx error counter. This results in a much higher Rx error count, but I am not sure what in the driver is causing these other error counters to be so high.

The excessive error count reported by the customer could be happening because there is a lot of interference in the customer's environment. The AP530 at my desk always reports a lot of errors on its radios due to interference in the building. There is a lot of stuff in the 2.4 GHz range like cordless phones, Bluetooth, etc. I have seen a lot less errors reported by WESM radios though, so it may be that the AP530 is just overly sensitive to some types of errors. Even if there are no clients connected, the AP is still receiving all the packets within receive range on that channel. It is one big broadcast domain and there are beacons from other APs, probe requests from other clients, traffic from other clients, etc.
J Vesterdahl
Regular Advisor

Re: PCM reports erroneous WLAN errors

Thanks for the effort, Steve.
Looks like my setup is healthy enough.
There is always one more bug ...