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

Rich Brown <richb.hanover@gmail.com> Thu, 05 March 2015 19:50 UTC

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From: Rich Brown <richb.hanover@gmail.com>
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Date: Thu, 5 Mar 2015 14:50:33 -0500
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To: curtis@ipv6.occnc.com
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Cc: "aqm@ietf.org" <aqm@ietf.org>, Dave Taht <dave.taht@gmail.com>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, bloat <bloat@lists.bufferbloat.net>
Subject: Re: [aqm] [Bloat] ping loss "considered harmful"
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On Mar 5, 2015, at 1:56 PM, Curtis Villamizar <curtis@ipv6.occnc.com> wrote:

> 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... 

For an easy (but imprecise) way test the HTTP response times, try Blip - http://gfblip.appspot.com/ (or read about it on github: https://github.com/apenwarr/blip) Blip sends short http requests to a couple hosts and measures the response time of the error pages. 

> 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
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