Auto Qos IOS config difference...

Unanswered Question
Jul 29th, 2010

We run auto qos in a few sites aorund the place, mainly on 2960s.

On  IOS version 12.2(25)FX after you enter the auto quos voip trust command, it puts the srr-queue bandwitdh share and srr-queue bandwidth shape commands under each interface.

I recently deployed an new 2960 running 12.2(53)SE2.  after entering the auto qos voip trust command i noticed that the srr-queue bandwidth shape command is missing from the interface config.  Only the bandwidth share command is there.

Also the command show mls qos interface queuing shows that the shaped queue weights is now 25 0 0 0 where in earlier versions it was 10 0 0 0

So, with the new version, is shaping enabled on the interface, even though the command is not specifically applied to the interface.  If not, does it need to be manually typed in?


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Jayakrishna Mada Thu, 07/29/2010 - 22:11


This is expected.

The final 0 0 0 in the shape command means that the other 3 queues do not operate in shaped mode, but are in shared mode.

If Priority queue is enabled queue 1 gets all the bandwidth if there is a packet in that Q. So there is no point in having shape command with priority-queue out command enabled.

if you look again the older version did not have "priority-queue out" enabled when you turn on quto qos. Hence they had share and shape command turn on, now they enable "priority-queue out" with auto qos hence shape is out.

It is always good that queues operate in shared mode. so you do have to enable anything at this point.

Hope that helps.


LucaSalvatore_2 Thu, 07/29/2010 - 23:07


however, isn't one of the purposes of the shape command to keep VoIP traffic smooth?  Without the shape command could voice traffic suffer from jitter?

Jayakrishna Mada Thu, 07/29/2010 - 23:52

When you use the shape command you gurantee the % bandwidth that you mention in the shape command, ideally you give some value to queue 1 which is the priority queue  where your voice-traffic maps (with out the priority-out command its just another queue) this is to make sure that the voice traffic gets the enough bandwidth all the time and share the remaining bandwidth among the other 3 queues.

priority-queue out gives you the best (low) jitter and latency.

Hope that clarifies your question.



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