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Cat3750 & Priority Queue

From guide:"The strict priority queue is enabled by configuring the fourth queue's weight parameter, as defined in the wrr-queue bandwidth command, to be 0"

Does it mean that after enable on interface #auto qos voip cisco-phone

i didn't enabled strict priority queue?


interface FastEthernet0/13

switchport mode dynamic desirable

mls qos trust device cisco-phone

mls qos trust cos

auto qos voip cisco-phone

wrr-queue bandwidth 10 20 70 1

wrr-queue min-reserve 1 5

wrr-queue min-reserve 2 6

wrr-queue min-reserve 3 7

wrr-queue min-reserve 4 8

wrr-queue cos-map 1 0 1

wrr-queue cos-map 2 2 4

wrr-queue cos-map 3 3 6 7

wrr-queue cos-map 4 5

priority-queue out



Re: Cat3750 & Priority Queue

When you enable auto-qos the strict priority queue is participating in srr. All four queues are used and the fourth (priority-) queue has at least 10% reserved for real-time traffic.

If you configure the priority-queue out command you enable a strict priority queue. The result is that the fourth queue no longer participates in the shaped/shared round robin process.

Re: Cat3750 & Priority Queue

I think you have a documentation cross-wire there.....

The 2950 is the only switch that has the strict priority queue enabled with the global command 'wrr-queue bandwidth' and setting the 4th queues weight to 0.

It looks like you have a 3550 switch there (based on the output). For a 3550 (and a 3750) you enable the ergress expedite queue with the interface command 'priority-queue out'. The 3550 & 3750 are different again though as the strict priority queues are the opposite way around (Q1 on 3750 & Q4 on 3550).

I suggest you check your documentation sources.....




Re: Cat3750 & Priority Queue

It has to be 3550 as Andy pointed out . Reason.

it uses a priority-queue out command ( applicable to (3550 / 3560 / 3750/2970 ) but uses Weighted round robin queues . 3750 / 3560 and 2970 use Shaped round robin queues and there are no wrr commands there.

The weight for the 4th queue has no meaning once you enable priorit-queue out command.

D-C3550-1A#sh mls qos interface fastEthernet 0/1 queueing


Egress expedite queue: ena

wrr bandwidth weights:


1 - 5

2 - 25

3 - 70

4 - 1 when expedite queue is disabled

Cos-queue map:


0 - 2

1 - 1

2 - 3

3 - 3

4 - 3

5 - 4

6 - 3

7 - 3

See how queue 4 mentions that weight only applies when priority queue is disabled. Sinc eyou have priority queue enabled , the weight for queue 4 does not matter and it becomes a "service until empty" queue.


Salman Z.

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