[Cake] de-natting & host fairness

moeller0 moeller0 at gmx.de
Mon Sep 26 04:54:09 EDT 2016

Hi Kevin,

this is like the missing puzzle piece, if you solved this, most home users might end up deep in your debt (without them realizing it of course).
Question, if I enable this on my link how will it deal with the typical differences between IPv4 and IPv6? I believe that the situation I have at home, NAT for IPv4 but no NAT for IPv6 (or if NAT, at least NAT with identifying last 64 bits of the IPv6 addresses, no port remapping games) is quite common now a days. I assume it will do the right thing for IPv4 but will it still do the right thing for IPv6 flows as well? And what if for $DEITY’s sake someone would insist on using a port-remapping NAT on IPv6?
If, what I assume it will do the right thing by default, I would vote for enabling this by default and introduce keywords to disable this if required (in what I assume to be one of cake’s main ideas use reasonable defaults that in general do the right thing, but also allow crazy stuff if need be).
Do you have any idea how expensive this is computationally? I realize that this is a tad hard to measure as cake will not simply reduce the available bandwidth when running out of CPU cycles but first will allow the latency to increase.

Best Regards

> On Sep 26, 2016, at 05:20 , Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:
> Greetings!
> A while back I started on a quest to make cake 'nat' aware as the lack of host fairness in a typical home router environment was the only thing that prevented cake from being the ultimate qdisc in my opinion.  This involves dealing with conntrack which on egress is easy (the kernel fills in a data structure for us), ingress is less clear.  I hacked something together but wasn't really happy with it.
> Another github user 'tegularius' presented some beautifully crafted code that did the lookups in a much neater way.  Originally it too had an 'ingress' lookup problem.  This was worked on and I hacked some conditional 'denat' options into cake & tc.
> For your 'delight' a denat cake https://github.com/kdarbyshirebryant/sch_cake/tree/natoptions along with a matching tc https://github.com/kdarbyshirebryant/tc-adv/tree/denat
> Typically I use 'dual-srchost srcnat' options on the egress interface, with 'dual-dsthost dstnat' in the ingress ifb interface.  In *brief* testing, bandwidth is shared fairly between hosts, and fairly by flow within each host.  And it's not crashed yet.
> Kevin
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