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Date: Mon, 9 Jul 2007 23:24:35 -0700
From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: Mike Silbersack <silby@silby.com>
Message-ID: <20070710062435.GA62925@troutmask.apl.washington.edu>
References: <20070709234401.S29353@odysseus.silby.com>
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Cc: Andre Oppermann <andre@freebsd.org>, Robert Watson <rwatson@freebsd.org>,
	current@freebsd.org, net@freebsd.org
Subject: Re: FreeBSD 7 TCP syncache fix: request for testers
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On Tue, Jul 10, 2007 at 12:20:49AM -0500, Mike Silbersack wrote:
> 
> I've found one of the causes of the network instability of FreeBSD 7; the 
> tcp syncache fails to retransmit SYN-ACK packets.  This causes interesting 
> problems when packet loss is experienced during connection setup.  The 
> symptoms that I have witnessed are twofold:
> 
> 1.  If the third part of the 3WHS is lost, the client will believe that 
> the connection is in the ESTABLISHED state, while the server will still 
> have the connection in the syncache.
> 2.  Subsequently, the above syncache entry will stay stuck in the syncache 
> forever.  If you attempt to re-use that same 4-tuple, the syncache will 
> ack the new SYN with the old sequence number.
> 
> Anyway, the attached patch simplifies the syncache structure a bit and 
> makes it retransmit properly.  I'd appreciate testing from anyone who has 
> experienced TCP problems with FreeBSD 7, as well as anyone who is pushing 
> significant traffic through FreeBSD 7.

Mike,

Thanks for tracking this problem down.  I can't test this patch
for a few weeks due to deadlines.  I'll run some tests when I can.