[Cake] Getting Cake to work better with Steam and similar applications

Dendari Marini dendari92 at gmail.com
Sat Apr 22 17:56:45 EDT 2017

Hello, thank you all for your replies!

For the overhead I'm gonna use "pppoe-llcsnap" (or "overhead 40 atm), as I
believe it's the one which should work best for my connection.

About the per-host fairness download issue: while it's kinda resolved I
still feel like it's mainly related to Steam, as normally downloading files
from PC1 and PC2 halved the speed as expected even at full bandwidth (so no
overhead, no -15%).

Anyway back to Steam: assuming the IP addresses aren't a big issue, what
steps should I follow to start filtering its traffic so it's considered
background? Would the DPI from the ER-X be any helpful?

On 22 April 2017 at 18:47, Sebastian Moeller <moeller0 at gmx.de> wrote:

> > On Apr 22, 2017, at 11:36, Jonathan Morton <chromatix99 at gmail.com>
> wrote:
> >
> >>> So please add “atm overhead 32" to cake on eth0 or “atm overhead 40”
> to cake instances on pppoe (these packets do not have the PPPoE header
> added yet and hence appear 8 bytes to small).
> >>
> >> Thanks for your help, will definitely use them. Just wondering if I use
> "pppoe-vcmux/bridged-llcsnap" on eth0 or "pppoe-llcsnap" on pppoe0 would
> have the same effect? Or are there some other "under-the-hood" changes when
> using them?
> >
> > On the pppoe interface, use pppoe-vcmux if your modem is set to use
> VC-MUX, or pppoe-llcsnap if it’s set to use LLC-SNAP (they might be
> described using slightly different terms, but should still be recognisable
> as one or the other).  This probably depends on your ISP, and may further
> vary regionally within the same ISP.
>         In my experience it is rather bothersome trying to get that
> information from one’s ISP, this is why I would recommend to follow the
> instructions on https://github.com/moeller0/ATM_overhead_detector and
> empirically measure the actual overhead. In that case one ends up with the
> numeric overhead, hence my inclination to use that number directly instead
> of looking into a table to translate that back into a symbolic keyword…
> especially since say for an overhead of 32 (and 36) there are two different
> encapsulation schees that add up to that number:
> case 32
>                 disp('Connection: Bridged, LLC/SNAP RFC-1483/2684');
>                 disp('Protocol (bytes): Ethernet Header (14), ATM LLC (3),
> ATM SNAP (5), ATM pad (2), ATM AAL5 SAR (8) : Total 32');
>                 disp('Connection: PPPoE, VC/Mux RFC-2684');
>                 disp('Protocol (bytes): PPP (2), PPPoE (6), Ethernet
> Header (14), ATM pad (2), ATM AAL5 SAR (8) : Total 32’);
> good luck divining which of those is in use if all you know is the numeric
> overhead...
> >
> > I really prefer to use the self-explanatory keywords (which is why I
> added them in the first place) instead of opaque magic numbers.  This is a
> point on which Sebastian has long disagreed with me.
>         True, but I am not going to re-hash that here again ;)
> >
> >>> Question: if you set the shaper’s to 50% of line rate (8.75/0.5?) do
> you still see that unfairness? And if you add “atm overhead 40” to cake on
> pppoe0 and set the shaper to 90% of line rates (15.75/0.9) how does the
> Steam affect per-host fairness? Also how transient are these connections
> team uses?
> >>
> >> Actually did more testing about this and it seems that as far I have
> set the bandwidth to ~15Mbps (so ~15% less of my max speed) and use the
> "nat" parameter, the per-host fairness works even without the "dual-host"
> and "overhead" parameters. I definitely find this very interesting, is this
> behaviour caused by the way Steam downloads games?
> >
> > By default, Cake uses triple-isolate mode, which uses information about
> both source and destination hosts to perform per-host isolation; this
> usually works well regardless of which side of the connection has the LAN
> hosts.  The “dual” modes let you specify that fact explicitly, making it a
> little more robust and predictable.
> >
> > Without overhead compensation, Cake will actually use more of the
> physical link than it thinks it does - by default it only accounts for raw
> IP or Ethernet packets, depending on the type of interface it’s attached
> to.  With full-size packets as in a bulk download, the difference is
> relatively small, so the 15% margin is just about sufficient to make things
> work.  But with small packets mixed in, the difference grows, such that
> Cake might no longer control the bottleneck with some traffic mixes.
>         All true, to elaborate a bit on the ATM specific issue, due to
> AAL5’s insistence that each ethernet frame is packaged into an integer
> number of ATM cells (where the unused octets are simply padded out) the
> worst case is something like 100%, if a hypothetical packet would only
> require 49 Bytes, it will still require two ATM cells of 53 bytes...
> >
> > The “conservative” keyword I recommended earlier (which is exactly
> equivalent to Sebastian’s recommendation of “atm overhead 48”) reverses
> that situation; Cake will then always end up using *less* of the physical
> link than it accounts for, which is safe for troubleshooting with.  The
> keyword is there specifically so that we do’t have to figure out the
> precise overhead profile before tackling more substantive issues.
>         Due to the boundary observation above, one other option is to
> start with the shaper set to 50% of link rate, that should have sufficient
> wiggle room for all realistic overheads… (but honestly on a known ATM link
> I would always run the ATM_overhead_detector to get the precise number).
> >
> > At any rate, it has nothing to do with Steam specifically.
> >
> >>> As far as I can tell cake can drill down to the required IP/TCP/UDP
> fields independent of whether there are VLAN tags or PPPoE headers so cake
> should not care (except for the different overhead specifications you need
> to add as stated above). BUT if instantiated on eth0 cake will see pppoe
> LCP packets and might decide to drop them, which can take down the link, so
> out of caution I would still instantiate on pppoe in your case.
> >>
> >> Yeah, with further testing it seems the interface wasn't the culprit
> but I'll still do all my testing on pppoe0 just to be safe.
> >>
> >> Anyway I was wondering if there's some kind of manual for Cake and the
> various parameters, I'm looking to set it up best way possible but there
> are some parameters which I'm not sure what they do (one of them being
> "ingress”).
> >
> > With the correct version of iproute2 installed, just issue “man
> tc-cake”.  That’s the official documentation.
> >
> > Currently it doesn’t have the ingress keyword yet.  That’ll be fixed
> soon.
> >
> >> Also while reading on the bufferbloat.net Cake page I noticed a
> possible "fix" for BitTorrent (by setting it as "background",
> https://www.bufferbloat.net/projects/codel/wiki/Cake/#diffserv-support),
> I'm wondering if this can be done with Steam too?
> >
> > It’s possible, if you can figure out which traffic is Steam in the first
> place, and write filters to match on it.  This is complicated by the fact
> that Valve runs a sophisticated CDN to handle their rather impressive
> bandwidth load.
> >
> > - Jonathan Morton
> >
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