I'm trying to understand the behaviour of class based weighted fair queue (CBWFQ) under particular conditions.
Say have 2 queues.
Queue 1 - bandwidth 50%
queue 2 - is the default queue bandwidth 10%
There is no LLQ
Policy is applied outbound.
For simplicity the interface bandwidth is 1mb.
What happens when both queues are full? How is the traffic split?
For arguments sake let's say that the other interface on the router is 100mb and its receiving both classes of traffic at rate of 20mb.
Now I understand that Queue 1 will have a reservation of 50% (500k). But how is the remaining 500k split?
In a 5:1 ratio or 50\50 split?
My understanding is excess available bandwidth is assigned in the same ratios, i.e. 5:1 in your example. This assumes all the other classes have explicitly defined bandwidths and they all would use 100%. I think I came across a Cisco reference that excess would be split equally across classes, i.e. 50/50 in your example, but believe the former, ratios, is correct. Reason being for this belief, CBWFQ seems to use the bandwidth setting to assign a "weight" to the class-queue (WFQ between classes), and as far as I can tell, this weight isn't adjusted when the class rate exceeds its bandwidth assignment.