netdev - Re: Weird TCP retransmit behaviour in recent kernels

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Message-ID: <alpine.LNX.2.00.1005161204380.3517@pentagram.it.hurts.ca>
Date:	Sun, 16 May 2010 12:08:16 -0400 (EDT)
From:	Michael Smith <michael@...ts.ca>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: Weird TCP retransmit behaviour in recent kernels

On Sun, 16 May 2010, Ilpo Järvinen wrote:

> On Fri, 14 May 2010, Michael Smith wrote:

>> It seems like when consecutive packets are lost, the SLES11
>> server retransmits the first packet when the timeout fires. The client
>> ACKs, but the server doesn't retransmit the next lost packet; instead,
>> it sends a couple more new packets, which don't get ACKed.

> This is where your problem is, they should get acked in a _compliant_
> network (with duplicate ACKs).

> Some have seen similar phenomena, every time it has been fault in some
> middlebox/peer that does not do what it should. You can disable frto
> using tcp_frto sysctl if you like, however, I disagree with you as I'm
> pretty sure there is some broken middlebox in the network (which is trying
> to be too intelligent).

Thanks - tcp_frto=0 works around the problem here. The network in the 
middle is provided by a number of other parties, so I can try to point 
them in the right direction, but unless Microsoft turns on FRTO by default 
sometime soon, I doubt they will have time to care. :)

Mike