From owner-freebsd-net@FreeBSD.ORG  Mon Oct 10 06:31:07 2005
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Date: Mon, 10 Oct 2005 01:31:03 -0500 (CDT)
From: Mike Silbersack <silby@silby.com>
To: Olivier Nicole <on@cs.ait.ac.th>
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References: <200510100622.j9A6MMbW014091@banyan.cs.ait.ac.th>
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Cc: freebsd-net@freebsd.org
Subject: Re: SYN limit
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On Mon, 10 Oct 2005, Olivier Nicole wrote:

> For some reason, it seems that the MySQL server only accepts 50
> connections to the same resource comming from the same client at one
> given time. 50 other connections are in SYN_SENT state.
>
> Any reason why this limit?

FreeBSD has no SYN rate limit, but you could be running into TIME_WAIT 
recycling issues.

Run a netstat on both the client and server, see if the port numbers 
match.  For example, see if the client is trying to connect to port 3549 
and the server has a TIME_WAIT socket on port 3549.  The connection is 
supposed to recycle, but under certain conditions it might not...

After doing that, try setting net.inet.ip.portrange.randomized=0 and see 
if the problem clears up at all.

Mike "Silby" Silbersack