netdev - Re: TCP fast retransmit

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Date:	Fri, 09 Dec 2011 15:43:31 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Esztermann, Ansgar" <Ansgar.Esztermann@...-bpc.mpg.de>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: TCP fast retransmit

Le vendredi 09 décembre 2011 à 14:34 +0100, Esztermann, Ansgar a écrit :
> On Nov 25, 2011, at 17:36 , Eric Dumazet wrote:
> 
> > Could you send a sample pcap of such problem, but please include full
> > tcp sesssion, from the first SYN packet, up to packets following
> > restransmits.
> 
> OK, I've got a dump now. It is rather large (>300MB), so it's probably not a good idea to send it to the list. Instead, you can find it here:
> http://wwwuser.gwdg.de/~aeszter/tcpstream.pcap
> 
> The capture has been taken in the sender, 10.208.9.87, with a capture filter on the receiver's IP address. OS is:
> % uname -a
> Linux mwolf 2.6.37.6-0.9-default #1 SMP 2011-10-19 22:33:27 +0200 x86_64 x86_64 x86_64 GNU/Linux
> 
> The first "strange" retransmission is in frame 166859, following ACKs in frames 166849 .. 166858. 
> 
> If I can do anything to reduce the amount of data, I will of course do so.
> 
> > A diff of "netstat -s" taken before your session and after your session
> > on receiver would help too, if receiver is not a loaded machine of
> > course.
> 
> Attached.
> 
> Thanks a lot,
> 
> A.
> 

It seems you have a lot of packet reorders.

Are you using multipath or some channel bonding ?



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