Cisco 3750 Auto-QoS Egress Discards

james.doukas · ‎12-19-2011

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 · ‎12-19-2011

Please post the output from typing:

show mls qos interface fa1/0/18 statistics

and

show mls qos maps

Joseph W. Doherty · ‎12-19-2011

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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 · ‎12-21-2011

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 · ‎12-22-2011

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 · ‎12-22-2011

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.