[Cake] Trouble with CAKE

Thibaut hacks at slashdirt.org
Fri Dec 13 09:13:34 EST 2019

Hi Jonathan,

Thanks for the quick reply.

December 13, 2019 3:02 PM, "Jonathan Morton" <chromatix99 at gmail.com> wrote:

>> On 13 Dec, 2019, at 3:43 pm, Thibaut <hacks at slashdirt.org> wrote:
>> I've been using CAKE on my DSL-connected Linux router for the last few years, and it worked well
>> until very recently. Two things happened:
>> 1) My ISP (French "Free") switched my DSLAM to native IPv6, which for the time being means that I
>> had to revert to using their set-top-box (Freebox) instead of the VDSL2 model I was using in bridge
>> mode until then (CAKE in "bridged-ptm ether-vlan" mode)
>> 2) I upgraded my router from 3.16 (Devuan Jessie) to 4.9 (Devuan ASCII)
>> Since then, no matter which setup I use, I cannot get CAKE to work as intended. Specifically, any
>> long-standing best effort stream (such as a remote rsync) will be throttled to a near grinding halt
>> even though there is no other significant traffic going on. Some random bursts can be seen (with
>> iftop) but nothing ever gets close to half the maximum bandwidth. This is notably affecting the
>> OpenWRT buildbots I'm hosting on this link.
> Old kernels, including 4.9 series, tend to be more problematic than the latest ones. If you can, I
> would recommend updating to a 5.x series kernel, in which Cake is an upstream feature. I won't
> presume to guess how best to achieve that with your distro.

Indeed. Given this is a relatively "security-sensitive" setup, I'd rather not diverge from distro (or run "unstable" for that matter).
Still, CAKE was previously working Just Fine(TM) on an even older kernel: 3.16...
> The good news is that Free.fr is among the relatively few ISPs who have actively tackled
> bufferbloat themselves. As a workaround while you sort this out, you should get reasonable
> performance just from using the Freebox directly.

Well, probably not with the antiquated Freebox model I have: a v5. I would also very much like to drop it to be able to connect again at VDSL2 speeds (I was getting 50/10 instead of the current 20/1) and save 75% on power usage (the Freebox is power hungry). But that's orthogonal to the current issue :)

What I could do for a test is temporarily revert back to the previous 3.16/Jessie setup (I have kept a backup) and see if I can reproduce the same behavior there, in which case I think that would definitely point in the general direction of a bad interaction with the Freebox tunnel?


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