Cisco 3750 Auto-QoS Egress Discards

[james.doukas]

Hello all,

I have an issue where I'm seeing output discards on pretty much all my ports configured for QoS. The switches are cisco WS-C3750V2-48PS running 12.2(50)SE1. There are four switches stacked using stack cables. The QoS implemeted was auto-qos with no modifications to the standard config. All ports are in queue-set 1. The phones connected are Cisco 7942's. Already did the standard check for speed duplex mismatch, crc's, runts, giants, etc...No discards before the QoS was applied. No bug ID's I could find regarding these switches and this IOS version. The one thing noticed is that 99% of all the drops are from queue's 2 and 4 or 1 and 3 doing the below command. Looking for any ideas.

**I've limited the cut and paste as to not clutter the discussion until someone requests something else**

Thanks,

James

show platform port-asic stats drop

Port 18 TxQueue Drop Statistics

  Queue 0

    Weight 0 Frames 0

    Weight 1 Frames 0

    Weight 2 Frames 0

  Queue 1

    Weight 0 Frames 0

    Weight 1 Frames 0

    Weight 2 Frames 1852

  Queue 2

    Weight 0 Frames 0

    Weight 1 Frames 0

    Weight 2 Frames 0

  Queue 3

    Weight 0 Frames 0

    Weight 1 Frames 0

    Weight 2 Frames 57788

interface FastEthernet1/0/18

switchport access vlan 100

switchport voice vlan 101

speed 100

duplex full

srr-queue bandwidth share 10 10 60 20

priority-queue out

mls qos trust device cisco-phone

mls qos trust dscp

auto qos voip cisco-phone

[Edison Ortiz]

Please post the output from typing:

show mls qos interface fa1/0/18 statistics

and

show mls qos maps

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Enabling QoS on a 3750 splits buffer resources across 4 queues instead of just 1 queue.  Likely the default buffer re-allocations doesn't well support your traffic in the 4 queues.  You may be able to mitigate the problem by re-assigning buffer resources, but that's not guaranteed.

[Richard Bradfield]

James,

I am also running 122(50) SE1 on some of my switches, I notice in your interface configuration there is not

"service-policy input AutoQoS-Police-CiscoPhone" which is one of the things generated by the Auto Qos command.

with the  sh platform port-asic stats drop

I get the following; BTW the switch has been up 33 weeks, so really not that many drops, most of the Ip phones are 7962s

I am just wondering if it is working as it should, what sort of PC traffic do you have on your interfaces, does anybody complain about slowness etc?

Port-asic Port Drop Statistics - Summary
========================================
  RxQueue 0 Drop Stats: 0
  RxQueue 1 Drop Stats: 0
  RxQueue 2 Drop Stats: 0
  RxQueue 3 Drop Stats: 0

  Port  0 TxQueue Drop Stats: 0
  Port  1 TxQueue Drop Stats: 0
  Port  2 TxQueue Drop Stats: 535404
  Port  3 TxQueue Drop Stats: 7149
  Port  4 TxQueue Drop Stats: 8572
  Port  5 TxQueue Drop Stats: 3011
  Port  6 TxQueue Drop Stats: 0
  Port  7 TxQueue Drop Stats: 66760
  Port  8 TxQueue Drop Stats: 0
  Port  9 TxQueue Drop Stats: 5983
  Port 10 TxQueue Drop Stats: 5867
  Port 11 TxQueue Drop Stats: 0
  Port 12 TxQueue Drop Stats: 7102
  Port 13 TxQueue Drop Stats: 0
  Port 14 TxQueue Drop Stats: 0
  Port 15 TxQueue Drop Stats: 2083
  Port 16 TxQueue Drop Stats: 419
  Port 17 TxQueue Drop Stats: 44784
  Port 18 TxQueue Drop Stats: 2300
  Port 19 TxQueue Drop Stats: 10876
  Port 20 TxQueue Drop Stats: 2271
  Port 21 TxQueue Drop Stats: 57697
  Port 22 TxQueue Drop Stats: 52418
  Port 23 TxQueue Drop Stats: 24695
  Port 24 TxQueue Drop Stats: 1729
  Port 25 TxQueue Drop Stats: 3720

[james.doukas]

Here are the stats after changing the SRR settings yesterday from 10.10.60.20

interface FastEthernet1/0/24

switchport access vlan 100

switchport voice vlan 101

srr-queue bandwidth share 10 20 10 60

priority-queue out

mls qos trust device cisco-phone

mls qos trust dscp

auto qos voip cisco-phone

spanning-tree portfast

YOW02-SWM-001#show platform port-asic stats drop fastEthernet 1/0/24

  Interface Fa1/0/24 TxQueue Drop Statistics
    Queue 0
      Weight 0 Frames 0
      Weight 1 Frames 0
      Weight 2 Frames 0
    Queue 1
      Weight 0 Frames 31512
      Weight 1 Frames 0
      Weight 2 Frames 1853
    Queue 2
      Weight 0 Frames 0
      Weight 1 Frames 0
      Weight 2 Frames 0
    Queue 3
      Weight 0 Frames 0
      Weight 1 Frames 0
      Weight 2 Frames 66351

[james.doukas]

Wait a minute. These may be old stats as I don't think you can clear the show platform counters like you can the show mls counters.