QOS input priority queue

[Emil Naklicki]

I am reviewing the latest Auto QOS settings and trying to wrap my head around ingress priory queue. So COS 5 is used for voice and according to the configuration below should be placed in queue 2 (Priority queue). However, I am not seeing any mapping for COS5 to any queue in this configuration. Is this a mistake or am I missing an implicit rule?

mls qos srr-queue input bandwidth 70 30
mls qos srr-queue input threshold 1 80 90
mls qos srr-queue input priority-queue 2 bandwidth 30
mls qos srr-queue input cos-map queue 1 threshold 2 3
mls qos srr-queue input cos-map queue 1 threshold 3 6 7
mls qos srr-queue input cos-map queue 2 threshold 1 4  < shouldn't this be 5?
mls qos srr-queue input dscp-map queue 1 threshold 2 24
mls qos srr-queue input dscp-map queue 1 threshold 3 48 49 50 51 52 53 54 55
mls qos srr-queue input dscp-map queue 1 threshold 3 56 57 58 59 60 61 62 63
mls qos srr-queue input dscp-map queue 2 threshold 3 32 33 40 41 42 43 44 45
mls qos srr-queue input dscp-map queue 2 threshold 3 46 47
 

[Francesco Molino]

Hi

What model of switch are you using and which IOS version?
With new version you shouldn't be able to modify the input queuing (for example on 3750, 2960)
Your dscp 46 is assigned to queue 2 but sure cos 5 is missing here.
Here a link that gives you an overview of default values:
https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2019/pdf/BRKCRS-2501.pdf

You can also check on Cisco documentation.

[Emil Naklicki]

I am using a few 3750's running software versions 12.2(55) SE12. I believe I have the ability to modify input queues as I have the following commands in my running configs.

mls qos srr-queue input cos-map queue 1 threshold 2 3
mls qos srr-queue input cos-map queue 1 threshold 3 6 7

However there may be some kind of default values since COS 5 is in fact mapped to queue 2

Sh MLS QOS maps cos-input-q

Cos-inputq-threshold map:
cos: 0 1 2 3 4 5 6 7
------------------------------------
queue-threshold: 1-1 1-1 1-1 1-1 1-1 2-1 1-1 1-1

However this is still confusing. Why is this set automatically to queue 2 threshold 1 while dscp 46 is set to queue 2 threshold 3? Shouldn't these typically belong in the same queue as COS 5 and DSCP 46 are typically mapped together?

This raises more questions. If I didn't have a DSCP 46 mapping to queue 2 threshold 3 then would it default to queue 2 threshold 1 similar to the behavior of COS5? And if so then this brings me back to my original question. Should there have been a COS 5 mapping to queue 2 threshold 3 that Cisco missed for SRND4 auto QOS?