Qos - mls qos

[Jerome C.]

Hi,

On my different switches (c2960s, c2960x, c3750x), I have this Qos : 

policy-map PM_QOS_MARKING_ACCESS
class CM_CIMPA_REALTIME_VOICE_TOIP
set dscp af31
class CM_CIMPA_REALTIME_VOICE_SKYPE
set dscp af31
class CM_CIMPA_PREMIUM_VIDEO_SKYPE
set dscp af31
class CM_CIMPA_PREMIUM_VIDEOCONFERENCE
set dscp af31
class CM_CIMPA_PREMIUM_D1INP
set dscp af31
class CM_CIMPA_DSCP-IN-D2INP
set dscp af21
class CM_CIMPA_DSCP-IN-D3INP
set dscp af11
class class-default
set dscp default

I have also this configuration about queue :

mls qos srr-queue output cos-map queue 1 threshold 3 5
mls qos srr-queue output cos-map queue 2 threshold 1 2 4
mls qos srr-queue output cos-map queue 2 threshold 2 3
mls qos srr-queue output cos-map queue 2 threshold 3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3 0
mls qos srr-queue output cos-map queue 4 threshold 3 1
mls qos srr-queue output dscp-map queue 1 threshold 3 46
mls qos srr-queue output dscp-map queue 2 threshold 1 16 18 20 22 25 32 38
mls qos srr-queue output dscp-map queue 2 threshold 2 24 26
mls qos srr-queue output dscp-map queue 2 threshold 3 48 56
mls qos srr-queue output dscp-map queue 3 threshold 3 0
mls qos srr-queue output dscp-map queue 4 threshold 1 8
mls qos srr-queue output dscp-map queue 4 threshold 3 10 12 14
mls qos queue-set output 1 threshold 2 70 80 100 100
mls qos queue-set output 1 threshold 4 40 100 100 100
mls qos

My question is : is-it mandatory to define these mls qos srr-queue output based on Cos and dscp-map ? What is the risk if I remove these line and keep only my policy-map to mark the traffic ? 

For example, on an equipment connected on one interface, when I try to download a file from our internal web server, I have a very poor performance and when I remove these lines, the performance to download the file is better..

BR

[Georg Pauwen]

Hello,

looking at the values used, it doesn't look like they were generated by Auto-Qos. So probably somebody, at some point, calculated these values manually. What does the rest of your configurtaion look like ?

Either way, the lines are not mandatory. If performance improves when you remove them, the values used are apparently not accurate anymore...

[paul driver]

Hello
If these QOS values are being honored within your qos for the estate then if you start changing them and you’re not sure why you are doing so then its possible you could incur issues at times of congestion in your network because changes at the qos edge then wont map to the upstream qos policy’s that would be expecting certain traffic marked with certain cos/dhcp values.

So if you make changes beaware of them and make sure those changes reflect anyother qos policys in your estate, I have been burnt many times with such changes not been recorded and having to T/S the issue