[Cake] tc-cake(8) needs to explain a common mistake

Dave Taht dave.taht at gmail.com
Fri Apr 3 14:49:48 EDT 2020

so nice to know cake has made it to russia!!!

On Fri, Apr 3, 2020 at 11:46 AM Alexander E. Patrakov
<patrakov at gmail.com> wrote:
> Hello,
> there is a recurring cargo cult pattern in many forums (e.g. OpenWRT):
> people keep suggesting various overhead compensation parameters to
> tc-cake without checking what's the bottleneck. They just assume that
> it is always related to the link-layer technology of the connection.
> This assumption is mostly incorrect, and this needs to be explained in
> the manual page to stop the cargo cult. E.g., here in Russia, in the
> past year, I had a 1Gbit/s link (1000BASE-X) but they shaped my
> connection down to 500 Mbit/s because that's the bandwidth that I paid
> for. I.e. the link from my router to the ISP equipment was not the
> bottleneck, it was the ISP's shaper.
> How about the following addition to the tc-cake(8) manual page, just
> before "Manual Overhead Specification"? Feel free to edit.
> General considerations
> -------------------------------
> Do not blindly set the overhead compensation parameters to match the
> internet connection link type and protocols running on it. Doing so
> makes sense only if that link (and not something further in the path,
> like the ISP's shaper) is indeed the bottleneck.
> Example 1: the ADSL modem connects at 18 Mbit/s, but the ISP further
> throttles the speed to 15 Mbit/s because that's what the user pays
> for, and does so with a shaper that has bufferbloat. Then, the "adsl"
> keyword is likely not appropriate, because the ISP's shaper operates
> on the IP level. The bandwidth needs to be set slightly below 15
> Mbit/s.
> Example 2: the ADSL modem connects at 18 Mbit/s, and the user pays for
> "as fast as the modem can get" connection. Then, the "adsl" keyword is
> relevant, and the bandwidth needs to be set to 18 Mbit/s.
> Example 3: the user has a 100BASE-TX Ethernet connection, and pays for
> the full 100 Mbit/s bandwidth (i.e. there is no shaper further up).
> Then, the "ethernet" keyword is relevant, and the bandwidth needs to
> be set to 100 Mbit/s.
> --
> Alexander E. Patrakov
> CV: http://pc.cd/PLz7

Make Music, Not War

Dave Täht
CTO, TekLibre, LLC
Tel: 1-831-435-0729

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