Lan QoS – going insane

I was doing some lan QoS yesterday evening. Specifically i wanted to mark some packets.
As usual, i wanted to create a policy-map, referencing some class-map, and then set the IP precedence value.

I tried to get this working for like 3 hours. I was verifying the behavior using the “sh policy-map interface ” command,
but it kept showing that there was no packets being matched.

As said, after 3 hours of searching the net for information, Doc CD and reading QoS exam guide, i was still nowhere. Finally
I went to #cisco on freenode.net. A clever guy pointed out that with some switch platforms, QoS is done purely in hardware, and it will
NOT set the counters. So, for me, this meant that my solution had worked all along, but my way of verification was wrong. A very valuable lesson
to learn!

  1. True the show “policy-map interface xxx” doesn’t work quite as expected on switches, with the 3550s you can put on an interface you can apply “mls qos monitor dscp 0 8 16 24 32 40 48 56” (if those were dscp values you were interested in monitoring) and using the “show mls qos interface xxx statistics” command and you can see details on packets that get classified, policed and dropped. Unfortunately the 3560 platform doesn’t support it in the same way.

    • Thanks man. Didnt know this, will be good to know in the future, unfortunally the lab is all 3560’s now so oh well. But thanks for the info!!

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