Cisco 3750 queue question

Unanswered Question
Jun 24th, 2007

Hi, I am looking at a 3750's configs and have a question. Below the two ingress queues and their WTD thresholds are defined:


mls qos srr-queue input threshold 1 8 16

mls qos srr-queue input threshold 2 34 66


Then, a little further down the configuration I see that queue 1 threshold 3 is being used:


mls qos srr-queue input dscp-map queue 1 threshold 3 32


What is confusing me is that I cannot see how/where threshold 3 is specified and according to the Cisco documentation I have read there are only two WTD thresholds anyway so how/why is this config referencing a 3rd threshold?

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Edison Ortiz Sun, 06/24/2007 - 18:23

There are 2 ingress queues and each queue has 3 thresholds.


http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/scg/swqos.htm


WTD Thresholds


The queues use WTD to support distinct drop percentages for different traffic classes. Each queue has three drop thresholds: two configurable (explicit) WTD thresholds and one nonconfigurable (implicit) threshold preset to the queue-full state. You assign the two explicit WTD threshold percentages for threshold ID 1 and ID 2 to the ingress queues by using the mls qos srr-queue input threshold queue-id threshold-percentage1 threshold-percentage2 global configuration command. Each threshold value is a percentage of the total number of allocated buffers for the queue. The drop threshold for threshold ID 3 is preset to the queue-full state, and you cannot modify it. For more information about how WTD works, see the "Weighted Tail Drop" section.

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