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Hierarchical Queueing Framework: queue limits and output drops

The QoS behavior in Cisco IOS has changed significantly with the introduction of the Hierarchical QoS Framework (HQF) in IOS release 12.4(20)T. Cisco is slowly producing in-depth articles describing the changes; the first one I’ve found documents the old and new output queue limits and output drops.

I’ve also added the link to this article to the Further reading section of my Queuing principles in Cisco IOS article.


  1. Oh, finally they started posting "something" detailed on CBWFQ (Be it HQF or pre-HQF) :) I remember i had to spend hours on simulation scenarios to find just how exactly CBWFQ works (which eventually appeared to be just WFQ with some steroids - ah well, they all come from GPS anyways :)

    However, I still cannot find any good explanation of pre-HQF: fair-queue + random-detect in class-default behavior in this article!

    Plus, I particularly enjoy this one: "In pre-HQF IOS images, generally speaking, any class with a bandwidth command will generally be prioritized against classes without bandwidth or priority based on the classes’ Weight". There are so many details hidden behind this generally sound sentence ;)

    However, the good news is the slow progress towards unified queuing solution and configuration syntax for all platforms/link technologies. Wish one day this could be true for hardware-optimized systems ;)
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