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New Member

Auto QoS on Cat 3750


when i turned on auto qos, on a FE interface of a catalyst 3750 as follows:

interface FastEthernet1/0/1

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

mls qos trust device cisco-phone

mls qos trust cos

auto qos voip cisco-phone

however, i realised that egress priority queuing is not enabled. See output below

Switch#sh mls qos interface fa1/0/1 queueing


Egress Priority Queue : disabled

Shaped queue weights (absolute) : 10 0 0 0

Shared queue weights : 10 10 60 20

The port bandwidth limit : 100

The port is mapped to qset : 1

i believe we need to turn on egress priority queuing using "priority out" interface command. Pls correct me if i am wrong..


Re: Auto QoS on Cat 3750


That is correct - you enable the expedite queue by using the 'priority-queue out' interface configuration command. By default, AutoQoS on the 3750 sets up queue 1 as a shaped queue, not a priority queue.

When you enter in the 'priority-queue out' command, the weight associated with the srr-queue is ignored.

Hope that helps - pls rate the post if it does.


New Member

Re: Auto QoS on Cat 3750

Hi Paresh,

Thanks for the reply. I was wondering why the "priority-queue out" command wasn't entered in automatically as it is required in VoIP sceneario..


Eng Wee


Re: Auto QoS on Cat 3750

Hi Eng Wee,

I believe the reason for not doing so is due to the inherent danger of having a priority-queue. If you are not using admission control mechanisms, there is always a danger that your priority queue traffic starves out the low-priority traffic.

If you are using appropriate admission control, you always have the option of tweaking the autoqos-generated config.

Hope that helps - pls rate the post if it does.


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