Re: [aqm] [Bloat] ping loss "considered harmful"

Curtis Villamizar <curtis@ipv6.occnc.com> Thu, 05 March 2015 18:59 UTC

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To: Dave Taht <dave.taht@gmail.com>
From: Curtis Villamizar <curtis@ipv6.occnc.com>
In-reply-to: Your message of "Tue, 03 Mar 2015 21:24:59 -0800." <CAA93jw4F7iffbTRUt5RFsF0wgoOAXPUVHdu7JESVq4uM17cm7A@mail.gmail.com>
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Date: Thu, 05 Mar 2015 13:56:33 -0500
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Cc: Wesley Eddy <wes@mti-systems.com>, bloat <bloat@lists.bufferbloat.net>, "Fred Baker \(fred\)" <fred@cisco.com>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] [Bloat] ping loss "considered harmful"
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In message <CAA93jw4F7iffbTRUt5RFsF0wgoOAXPUVHdu7JESVq4uM17cm7A@mail.gmail.com>
Dave Taht writes:
 
> My point was A), I have seen tons of shapers out there that actually
> prioritize ping over other traffic. I figure everyone here will agree
> that is a terrible practice, but I can certainly say it exists, as it
> is a dumb mistake replicated in tons of shapers I have seen... that
> makes people in marketing happy.
>  
> Already put up extensive commentary on that bit of foolishness on
> "wondershaper must die".


Its possible to detect such a shaper prioritizing ICMP echo/reply by
doing a an HTTP fetch concurrent with a ping and then and see if the
TCP data packet get significantly delayed relative to the ICMP echo
and echo reply packets.  You'd have to do a tcpdump and match the ICMP
echo to the echo reply and see if later the ICMP RTT looks very
different from the TCP RTT.  It might be that the SYN and SYN ACK are
not delayed but the plain old TCP date packets are.

If anyone has a small amount of spare time and wants to put together a
shell script its certainly doable.

Curtis