netdev - Re: TCP fast retransmit issues

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Date:   Wed, 26 Jul 2017 15:42:42 +0200
From:   Willy Tarreau <w@....eu>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Klavs Klavsen <kl@...n.dk>, netdev@...r.kernel.org
Subject: Re: TCP fast retransmit issues

On Wed, Jul 26, 2017 at 06:31:21AM -0700, Eric Dumazet wrote:
> On Wed, 2017-07-26 at 14:18 +0200, Klavs Klavsen wrote:
> > the 192.168.32.44 is a Centos 7 box.
> 
> Could you grab a capture on this box, to see if the bogus packets are
> sent by it, or later mangled by a middle box ?

Given the huge difference between the window and the ranges of the
values in the SACK field, I'm pretty sure there's a firewall doing
some sequence numbers randomization in the middle, not aware of SACK
and not converting these ones. I've had to disable such broken
features more than once in field after similar observations! Probably
that the Mac doesn't advertise SACK support and doesn't experience the
problem.

Willy