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Date: Fri, 8 Apr 2016 15:51:24 +1000 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: Dr Josef Karthauser <joe@truespeed.com>
cc: FreeBSD Stable <stable@freebsd.org>, freebsd-net@freebsd.org
Subject: Re: IPFW with NAT : Problems with duplicate packets on FreeBSD
 10.3-RC3
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On Thu, 7 Apr 2016 17:08:38 +0100, Dr Josef Karthauser wrote:

[ AppleMail msgs fail to quote properly in pine, so a partial quote: ]

 > Looks like the first packet is being retransmitted, which means that 
 > the nat is probably misconfigured and the TCP connection is broken in
 > some strange way.

 > Does anyone have a clue as to where to look? The ipfw rules are
 > simple enough - what have I missed?

Do you have TSO enabled on that NIC?  If so, see ipfw(8) BUGS, third 
last para.  If not, no idea ..

cheers, Ian