Catalyst QoS, priority -queue value, percentage of bandwidth or memory

Unanswered Question
May 22nd, 2009

I'm working on a 6500 with sup 720 running 12.2.33SXI code. What is the value specified by the priority-queue queue-limit command. The switch states its a weight, and the documentation states its a percentage, but of what?

I think its a percentage of the buffer memory allocated to the port, but am not 100% sure, and I cannot find a definitive answer on CCO.

Andy

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Anonymous (not verified) Thu, 05/28/2009 - 08:01

Ratio of priority queue weight: valid values are from 1 and 100 percent. The percentage of priority traffic on the network. Use the estimated percentages as queue weights

nate-miller Mon, 06/01/2009 - 13:27

Given that wrr-queue bandwidth ALSO exists, I've always thought of the bandwidth command as the ratio of time servicing a particular queue, and the queue-limit as the depth of the buffer dedicated to that particular queue.

That "weight" is a confusing term to me- I'm sure it means something in context, but I haven't figured that context out yet.

aacole Tue, 06/02/2009 - 03:14

After reading through different documents my understanding of these commands is:

On a card that supports 1p7q4t.

wrr-queue queue-limit 25 15 15 10 10 10 10

priority-queue queue-limit 5

All these values add up to 100% of the TX buffer size. As there are 8 queues, consisting of 1 priority and 7 standard, these 2 commands allocate the buffer space between each queue.

wrr-queue bandwidth 10 20 30 40 40 70 70

This command instructs the switch to send the specified number of packets in each of the standard queues in order of priority. So, any packet in the priority queue gets tramsmitted first, then 10 packets from the first standard queue, 20 from the second and so on.

Depending on which documents or books you refer to gives different explanations for the use of these commands, the Cisco documentaion refers to weights, not packet counts.

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