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OPERATIONAL DEFECT DATABASE
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Intermittently, an access point may fail to transmit data frames out its radio interface. With client tracing enabled on the AP, the AP indicates that it thinks that it is transmitting; however, an over-the-air packet capture does not see these frames. For example, DNS may fail - with the AP showing that it thinks it it sending the DNS REPLY packets out the radio: Jul 3 02:11:35 kernel: [*07/03/2020 02:11:35.9609] [1593742295:960956] [AP3C51.0E40.AAEE] [9c:da:3e:91:ba:db] [D:W] DNS REPLY : id 31337 opcode 0 But this packet is not seen in the OTA sniff, and is not received by the client. Similar failures are seen with downstream DHCP OFFER, ARP response, etc. packets being dropped by the AP radio. To determine whether this specific bug is being seen on an access point, issue the following AP-COS command at some intervals, while the symptoms are being seen: terminal monitor show interfaces dot11Radio 1 memory firmware [ wait a while ] show interfaces dot11Radio 1 memory firmware Then search the output for: q_stuck_rc2 If this radio problem is NOT being seen, the counter will remain 00000000: Dec 20 22:43:02 kernel: [*12/20/2021 22:43:02.6711] q_stuck_rc2: 00000000
Seen with 11ac MU-MIMO enabled, on an AP of one of the following models: 2800/3800/4800/1560/6300. This bug does not apply to any other AP model.
Temporary workaround: reboot the AP. Permanent workaround: Disable 11ac MU-MIMO on all WLANs. There is no need to disable 11ax Down Link or Up Link MU-MIMO, as this bug does not affect 11ax APs. In AireOS: for each WLAN: in the CLI: config wlan disable config wlan mu-mimo disable config wlan enable in the GUI: WLANs > > Advanced Uncheck "11ac MU-MIMO" > Apply In 9800/EWC IOS-XE: for each WLAN: In the CLI: config terminal wlan shutdown no mu-mimo no shutdown in the GUI: Configuration > Tags & Profiles > WLANs Uncheck 11ac MU-MIMO Update & Apply to Device
This commit CSCvv78719 does not fix the root cause of the problem, but implements a workaround: once the AP detects that the radio transmission have stalled, it will reset the radio, restoring communications. With this CSCvv78719 workaround, intermittent transmission stalls of 10-20 seconds or so may be experienced. Once running code with the CSCvv78719 commit: to determine whether the workaround resets are occurring, issue the AP commands show controller dot11radio 0 show controller dot11radio 1 and look for the "Radio RC stats" section. If there is a "Failure:" section immediately below, and if it shows 47 and/or 48 as a failure code, then this indicates that the CSCvv78719 workaround has kicked in. To get the fix for the underlying problem with 11ac MU-MIMO, which is causing the transmission stalls in the first place, upgrade to code with the CSCwa73245 fix. If transmission stalls (as seen in the q_stuck_rc2 counter) are being experienced, but 11ac MU-MIMO is not enabled, then CSCwa73245 is not applicable. However, the workaround implemented via this bug CSCvv78719 will still be effective.