qos lan clarification

nizarjafri · ‎04-15-2011

Hi,

From this link http://www.cisco.com/en/US/products/hw/switches/ps5023/products_tech_note09186a0080883f9e.shtml

I found this exemple for Scheduler Configuration:

Rack1SW3(config-if)#srr-queue bandwidth share 1 75 25 5 Rack1SW3(config-if)#srr-queue bandwidth shape 3 0 0 0 Cisco Catalyst 3750 egress queue does not support Low Latency Queueing (LLQ). It supports priority queueing. When you configure priority-queue out, queue 1 is always serviced when it has a packet.

Rack1SW3(config-if)#srr-queue bandwidth share 1 75 25 5 Rack1SW3(config-if)#srr-queue bandwidth shape 3 0 0 0 Rack1SW3(config-if)#priority-queue out When you configure this command, the SRR weight and queue size ratios are affected because there is one fewer queue participating in SRR. This means that weight1 in the srr-queue bandwidth shape or the srr-queue bandwidth share command is ignored (not used in the ratio calculation).

Question:

It means that once we apply priority-queue out, 33% that we guarantee for the queue 1 and the shared bandwidth for the other queues are ignored srr- queue bandwidth share 1 75 25 5 srr-queue bandwidth shape 3 0 0 0, and the queue 1 (priority queue) will get the total of bandwidth and not only 33%.

So to guarantee the share and the shape we cannot apply the priority queue??

Best regards

Nizar

mlund · ‎04-18-2011

Hi Nizar

You are correct, when You configure priority queue , queue 1 will be served first as long there are packets in the queue.

That meens that theorethicaly, if there are enough packets matching the priority queue, it can take all available bandwidth.

However, the bandwidth share 1 75 25 5, it's only first queue number that is ignored. The other three queue numbers are valid, if the priority queue is not eating up all memory ;-)

/Mikael