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llq with cbwfq question

Hi Experts,

I just need to verify the below.

I have llq with cbwfq set up and applied to my wan interface, if the llq bucket is empty, no llq traffic passing through, but high cbwfq traffic, will the cbwfq traffic consume the llq bucket?

I was just thinking if the answer is no and i have no voice traffic but a lot of data traffic. And say i have allotted 30% to llq.  Then does that mean that my link is already congested at 70%?  Wouldn't it make sense for the excess data traffic to consume some of the llq space if there are no llq traffic?

I can't seem to find any formal document by Cisco on this particular interaction between llq and cbwfq.  I can't find a cisco doc stating categorically that cbwfq will never use the llq bucket even if it is empty.

Thanks in advance.

Cisco Employee

llq with cbwfq question


During non-congestion periods each class can use unused bandwidth from other queues  - even from priorities:


Which Traffic Classes Can Use Excess Bandwidth?

Although the bandwidth guarantees provided by the bandwidth and priority commands have been described with words like "reserved" and "bandwidth to be set aside", neither command implements a true reservation. In other words, if a traffic class is not using its configured bandwidth, any unused bandwidth is shared among the other classes.


This is taken from this document:

It seems to be explaining LLQ and CBWFQ in fairly good details.

Hope this helps,