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Walkthrough Wednesdays

CSCuy23951 - Priority Packets Randomly Fall Under Class-Default Over *VWIC*

Just to add some notes on the issues we experienced related to this bug - we had one-way voice audio issues (outbound from the site so our users could not hear it) where audio was garbled, missing, or sounded like wind blowing over the audio.  We have a 2911 router running "c2900-universalk9-mz.SPA.153-3.M5.bin" code.  In the bug notice, it states that removing the shaping results in the problem not occurring, but just to clarify what we have seen, it has solved the voice audio issues, but it has also started classifying other traffic (not service-affecting) with our QoS policy where many higher queues have a small number of packets being placed in default - see below the AFXX DSCP values that end up in the default queue.  This should only transmit default these other DSCP categories should be in higher queues - so removing shaping changes the behavior and solves the audio issue, but this bug still affects the QoS policy - our QoS policy is identical on 100+ WAN routers on the same MPLS network, but this behavior only occurs on sites with a single WAN T1:

Class-map: class-default (match-any) 
      41160888 packets, 47835376202 bytes
      30 second offered rate 1682000 bps, drop rate 298000 bps
      Match: any
      queue limit 256 packets
      (queue depth/total drops/no-buffer drops) 69/6590448/0
      (pkts output/bytes output) 38164090/41040856611
      bandwidth remaining 4%
        Exp-weight-constant: 9 (1/512)
        Mean queue depth: 145 packets
        dscp       Transmitted         Random drop      Tail drop          Minimum        Maximum     Mark
                pkts/bytes            pkts/bytes       pkts/bytes          thresh         thresh     prob
        default 38155948/41039729557 443891/625277642 6146404/8682814051        160           192  1/10
        af11         959/236862          0/0              0/0                 32            40  1/10
        af12          32/7363            0/0              0/0                 28            40  1/10
        af13         861/221856          0/0              0/0                 24            40  1/10
        af21        2089/246377          0/0              0/0                 32            40  1/10
        af23         596/73051           0/0              0/0                 24            40  1/10
        af31         225/11512           0/0              0/0                 32            40  1/10
        af32        2817/279740          0/0              0/0                 28            40  1/10
        ef           563/50293           0/0              0/0                 36            40  1/10

Jose Castillo
Cisco Employee

Hi, Brent:

Thank you for sharing your experience, it varies a bit but indeed affects all VWICs, with 1 port, 2 or 4, but it depends on Interface Queues to experience the problem.

I was the one writing the bug, so if any question let me know.

There is a fix already integrating this fix. My suggestion is to upgrade to this version or wait for future releases in different trains.

15.4(3)M6a CCO by 7/29/2016  //

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