FreeBSD 7 TCP syncache fix: request for testers
sgk at troutmask.apl.washington.edu
Tue Jul 10 06:26:04 UTC 2007
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.
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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