netdev - Re: [PATCH] TCP FIN gets dropped prematurely, results in ack storm

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Date:	Tue, 1 May 2007 22:25:06 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] TCP FIN gets dropped prematurely, results in ack storm

On Tue, May 01, 2007 at 10:20:07PM +0400, Evgeniy Polyakov (johnpol@....mipt.ru) wrote:
> On Tue, May 01, 2007 at 11:13:54AM -0400, Benjamin LaHaise (bcrl@...ck.org) wrote:
> > Hello,
> > 
> > While testing a failover scenario, I managed to trigger an ack storm 
> > between a Linux box and another system.  Although the cause of this particular 
> > ACK storm was due to the other box forgetting that it sent out a FIN (the 
> > second node was unaware of the FIN the first sent in its dying gasp, which 
> > is what I'm trying to fix, but it's a tricky race), the resulting Linux 
> > behaviour wasn't very robust.  Is there any particularly good reason that 
> 
> One of the packets sent by broken 1.1 host has incorrect checksum, so it
> will be dropped by 2.2 system in theory, could that packet somehow break
> 2.2 stack's state machine?

It seems so, 2.2 stack expects i-1 sequence number, so when you add fin
into both (i-1)'th and i'th packets, 2.2 system correctly completes session
thinking that i-1 is the real last message, which is not.

-- 
	Evgeniy Polyakov
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