MLS QOS on 2960S

[b-ulrich1]

Enabling MLS QOS on 2960S seems to "throttle" bandwidth when using a specific Mitel 5320 phone.  I have a PC behind the Mitel and the performance is way slower.  Validated via a speed test.  Once I remove the MLS QOS globally, the performance is greatly improved, about doubled.  This is causing some issues as users with this particular phone attached with a PC behind the phone are starting to complain.  What could be causing this or what settings to overcome this?

[Ashwani Mantoo]

What license you are using on 2960S switch ?

can you share the outputs of:

1. show version

2. show mls qos 

3. show run int <int-id> --- where the mitel phone is connected to

4. show ip int br | ex unass

5. show int <int-id> --- where the phone is connected to

6. show mls qos int <int-id> statistics

This should help us to isolate the issue.

BR,

Ashwani

[b-ulrich1]

Attached are some of the outputs.  What I am looking for is that one or two interface settings that will modify this behavior.  If not, I will just remove the mls qos globally.

[Ashwani Mantoo]

1. You are not using Cisco IP phones, so remove the statement from the port config:

mls qos trust device cisco-phone

2. Try to disable DSCP rewrite option by:

conf t 

no mls qos rewrite ip dscp

end

3. clear the counters and check if we are dropping packets. if yes, we need to tweak the QoS settings to get it working without any issues.

4. Once you clear the counters, please send the outputs after 10 minutes and after testing the scenario again:

a. show int <int-id>

b. show mls qos queue-set

c. show mls qos int <int-id> statistics

BR,

Ashwani

[Joseph W. Doherty]

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Posting

Enabling QoS on a 2960/3560/3750, using defaults, often results in slow transfer performance.  This because the default buffer settings often increase drop rates in the newly enabled egress queues.  Manual buffer tuning might mitigate.