[Cake] Thinking about ingress shaping & cake

Jonathan Morton chromatix99 at gmail.com
Fri Apr 10 10:14:51 EDT 2020

> On 10 Apr, 2020, at 4:16 pm, Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:
> I have a 80/20mbit FTTC line into the house.  Egress shaping/control with cake is simple, easy, beautiful and it works.  Tell it to use 19900Kbit, set some min packet size, a bit of overhead and off you go.  Ingress has more problems:
> Assuming I do actually get 80Mbit incoming then the naive bandwidth setting for CAKE would be 80Mbit.  Cake internally dequeues at that 80Mbit rate and therefore the only way any flows can accumulate backlog is when they’re competing with each other in terms of fairness(Tin/Host) and quantums become involved…I think.

No.  If the dequeue rate is never less than the enqueue rate, then the backlog remains at zero pretty much all the time.  There are some short-term effects which can result in transient queuing of a small number of packets, but these will all drain out promptly.

For Cake to actually gain control of the bottleneck queue, it needs to *become* the bottleneck - which, when downstream of the nominal bottleneck, can only be achieved by shaping to a slower rate.  I would try 79Mbit for your case.

 - Jonathan Morton

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