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From: Jonathan Morton <chromatix99@gmail.com>
To: d@taht.net (Dave Täht)
Cc: bloat-devel <bloat-devel@lists.bufferbloat.net>,
	bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] shaper team forming up
Date: Mon, 14 Mar 2011 21:55:01 +0200	[thread overview]
Message-ID: <5BC42741-852B-4699-BA5D-D70B8D610D96@gmail.com> (raw)
In-Reply-To: <87wrk1a4gx.fsf@cruithne.co.teklibre.org>


On 14 Mar, 2011, at 9:26 pm, Dave Täht wrote:

> Over the weekend, Dan Siemons uncovered a possible bad interaction
> between ECN and the default pfifo_fast qdisc in Linux.
> 
> http://www.coverfire.com/archives/2011/03/13/pfifo_fast-and-ecn/

This seems to be more complicated that it appears.  It looks as though Linux has re-used the LSB of the old TOS field for some "link local" flag which is used by routing.

It's not immediately obvious whether pfifo_fast is using this new interpretation though.  If it isn't, the fix should be to remove the RTO_ONLINK bit from the mask it's using on the tos field.  The other half of the mask correctly excludes the ECN bits from the field.

 - Jonathan


  reply	other threads:[~2011-03-14 19:55 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-14 19:26 Dave Täht
2011-03-14 19:55 ` Jonathan Morton [this message]
2011-03-14 20:24   ` Eric Dumazet

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