[Cake] dual-src/dsthost unfairness, only with bi-directional traffic

[Jonathan Morton]

> On 3 Jan, 2019, at 6:15 am, Georgios Amanakis <gamanakis at gmail.com> wrote:
> 
> It seems if both clients are having bidirectional traffic, dual-
> {dst,src}host has the same effect as triple-isolate (on both lan and
> wan interfaces) on their bandwidth.

> This shouldn't happen though, or am I wrong?

If both clients are communicating with the same single server IP, then there *should* be a difference between triple-isolate and the dual modes.  In that case triple-isolate would behave like plain flow isolation, because it takes the maximum flow-load of the src and dst hosts to determine which dual mode it should behave most like.

Conversely, if the clients are communicating with a different server IP for each flow, or are each sending all their flows to one server IP that's unique to them, then triple-isolate should behave the same as the appropriate dual modes.  This is the use-case that triple-isolate assumes in its design.

It's also possible for triple-isolation to behave differently from either of the dual modes, if there's a sufficiently complex pattern of traffic flows.  I think those cases would be relatively unusual in practice, but they certainly can occur.

I'm left wondering whether the sense of src and dst has got accidentally reversed at some point, or if the dual modes are being misinterpreted as triple-isolate.  To figure that out, I'd need to look carefully at several related parts of the code.  Can anyone reproduce it from the latest kernels' upstream code, or is it only in the module?  And precisely which version of iproute2 is everyone using?

 - Jonathan Morton