Date: Mon, 9 Jul 2007 23:24:35 -0700 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: Mike Silbersack <silby@silby.com> 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 Message-ID: <20070710062435.GA62925@troutmask.apl.washington.edu> In-Reply-To: <20070709234401.S29353@odysseus.silby.com> References: <20070709234401.S29353@odysseus.silby.com>
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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.
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