C3850 High Output Drops After Auto QOS

[DJX995]

Cisco IOS XE Software, Version 16.09.04

After enabling auto QOS on my 3850, I'm showing high output drops and experiencing dropped packets streaming data from servers attached to a LACP group.

The only QOS setting on the interfaces is auto qos trust dscp.

From some quick research on the Internet, some people said I should apply this command: qos queue-softmax-multiplier 1200. I have with slightly worse results.

I had a similar issue on my 3750X and was able to work around it by adding this command to each interface: queue-set 2

I'm open to any and all suggestions.

Thanks!

[jalejand]

Catalyst 3k and 9k trust DSCP by default, no qos needed.
From the queue config stat I see that the buffer assignment on the ports increased. To allow the class-default to take advantage of most hardware buffers, just disable qos, dscp markings won't change.

interface GigabitEthernet1/0/3
 no switchport
 ip address 10.1.1.18 255.255.255.252 ------------ No QoS configured
 ip pim sparse-mode
 ip router isis
end

Border-CP-05-3850-02#show pla sof fed sw active qos qs int gi 1/0/3
QoS subblock information:
  Name:GigabitEthernet1/0/3 iif_id:0x00000000000038 iif_type:ETHER(146)
  qsb ptr:0xffdca863c8
  Port type = Wired port
  is_uplink:false init_done:1
  FRU events: Active-0, Inactive-0
  trust_enabled:true trust_type:TRUST_DSCP ifm_trust_type:3 ----------- Default state is TRUST_DSCP
  LE priority:13 LE tablemap handle(in, out): (0,0)
  Stats (plc,q) export counters (in/out): 0/29
  Policy Info:
    Ingress Policy:nil
    Egress Policy:nil
    TCG(in,out):((nil), (nil))
  Policer Info: Aggregate
    Ingress policer block: Not allocated
    Egress policer block: Not allocated
    Instance Handle: Not allocated
  Policer Info: Microflow
    Ingress policer block: Not allocated
    Egress policer block: Not allocated
    Instance Handle: Not allocated
  Queueing Info:
    def_queuing = 0, shape_rate:0 interface_rate_kbps:1000000
    Port shaper:false
    lbl_to_qmap_index:0

[DJX995]

I would really like to take advantage of QOS but only if the link is saturated. It would be really nice to have voice or other tagged traffic take priority over SMB (unclassified) traffic but I don't see a reason to drop SMB traffic (like it is now) if there is more than enough bandwidth on the link.

Did the buffer assignment increase after I rebooted with: "qos queue-softmax-multiplier 1200"?

[paul driver]

Hello

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@DJX995 wrote:

Last clearing of "show interface" counters never

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Clear the interface counters and check again it maybe its historical dropping of packets you may not have an issue?

[DJX995]

Oh, I most definitely have an issue. Not just going by stats here. Can't stream audio or video files from an SMB share without buffering.