Verifying QOS on Catalyst3750

Unanswered Question
Feb 7th, 2007

I have configured qos on a Cat3750 and my intention is to prioritize Voice(dscp=46) traffic on a specific interface(Fa1/0/44) . I have issued some "show mls qos ..." commands(are attached) . Can anyone explain me the output of the command "show mls qos interface Fa1/0/44 statistics" command . In short I am wondering if this QOS-setup is really working . Any other interesting verification commands for Cat3750's ?

Thanks in advance.

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jkeeffe Thu, 02/08/2007 - 07:27

The counters are showing you what the switch port sees as regards to DSCP and COS markings on packets incoming and outgoing on that port. For instance the 'dscp:incoming' list shows 20550467 dscp'0' packets and 522603316 dscp '1' packets. The row description '0 - 4' tells you what the five columns to the right are, ie. 1st column = dscp 0, 2nd column = dscp 1, last colume = dscp 4.

Continue this down and you will see 108470084 packets that were recognized as dscp 46 (your voice packets. Read the cos incoming and outgoing counters the same.

Your 'priority-queue out' statement overrides the srr-queue bandwidth commands and insures that any/all dscp 46 or cos 5 packets (the voice packets) will get serviced first if there is congestion on that port.

Hope this helps.

lldemeyer Thu, 02/08/2007 - 08:33

Thanks for the explanation , now I understand how to interpret the colums !

One more question ,if you don't mind? On interface Fa1/0/44 I have 2 srr-queue bandwidth commands one with keyword 'share' and one with keyword 'shape' . Reading the manual it states that the srr-queue bandwith shape takes precedence over the 'share' one .

So in my example Q1(prior) takes 1/3 of the bandwidth and the rest is shared by the 3 other Queues. Is the rest evenly shared or per 'share' command value ( Q2=70, Q3=25 , Q4=5) ?

jkeeffe Fri, 02/16/2007 - 06:51

You're into areas that I'm not that familiar with and so I can't comment. I do know that it is confusing when reading the manual concerning how the numbers in the SRR config work. I seem to remember that one of the numbers is actually an inverse ratio, like a 2 is 50%, a 3 is 30%.

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