Hi Thibaut,
so ADSL is both special and precious, may I recommend to follow the
instructions on https://github.com/moeller0/ATM_overhead_detector? This will
either confirm the overhead settings, or more likely "explode" if the freeebox
truely tunnels all IPv4 data through IPv6. In both cases the results should be
interesting. As a quick test, what is the textual output from the "Share Your
Results" box on https://www.speedguide.net/analyzer.php?
I would not be amazed if the issue might be related to having a whoping 40
bytes more of unaccounted for per-packet-overhead (in combination with
ATM/AAL5's lovely per packet padding). But that might all be moot if it is/was
caused by a kernel issue.
Best Regards
Sebastian
> On Dec 13, 2019, at 14:43, Thibaut <[email protected]> wrote:
>
> Hi list,
>
> 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.
>
> In details:
>
> $ uname -a
> Linux rapid-ts1 4.9.0-11-686 #1 SMP Debian 4.9.189-3+deb9u2 (2019-11-11) i686
> GNU/Linux
>
> Cake commit: 183b320 RFC 8622 diffserv3, 4 & 8 LE PHB support
>
> cake setup on the wan iface: bandwidth 1Mbit diffserv3 dual-srchost nat
> nowash ack-filter split-gso bridged-vcmux no-sce
> the available ATM uplink bandwith is 1.2Mbps, I tried going as low as
> 700kbps, disabling ack-filter and setting "conservative" to see if it would
> make a difference, it wouldn't in any significant way: the upload would still
> be severely throttled. I also tried disabling the ingress leg to get that out
> of the equation: also no difference.
>
> As I broke rule #1 of any setup upgrade (by changing both the link - VDSL to
> ADSL - and the running kernel), I can't tell for sure where the fault lies;
> however I must add something about the "native IPv6 DSLAM" bit:
>
> Free uses map-e/map-t, i.e. ipip6 tunnels on its native v6 DSLAMs. The
> Freebox still offers a public IPv4 to the connected router, but inside the
> Freebox there is an ipip6 tunnel setup to encapsulate the IPv4 traffic into
> IPv6, a tunnel over which I have no control. I wonder if this encapsulation
> and its associated overhead could be throwing CAKE computations off? FWIW, my
> router now operates in dual-stack mode, with both a public IPv4 and a public
> IPv6 (although for the time being my LAN remains IPv4 only).
>
> I haven't (yet) found a way to connect directly to the DSLAM without the
> Freebox (using my VDSL modem as I did before), so I can't get around this
> particular blackbox.
>
> I hope this provides enough detail, I'm happy to expand as needed: I would
> really want my CAKE back :)
>
> Cheers,
> Thibaut
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