From owner-freebsd-net@freebsd.org  Thu Jun  9 13:06:05 2016
Return-Path: <owner-freebsd-net@freebsd.org>
Delivered-To: freebsd-net@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0D764B6EEC5;
 Thu,  9 Jun 2016 13:06:05 +0000 (UTC) (envelope-from slw@zxy.spb.ru)
Received: from zxy.spb.ru (zxy.spb.ru [195.70.199.98])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id C60F71B7C;
 Thu,  9 Jun 2016 13:06:04 +0000 (UTC) (envelope-from slw@zxy.spb.ru)
Received: from slw by zxy.spb.ru with local (Exim 4.86 (FreeBSD))
 (envelope-from <slw@zxy.spb.ru>)
 id 1bAzer-0005gL-J2; Thu, 09 Jun 2016 16:06:01 +0300
Date: Thu, 9 Jun 2016 16:06:01 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Kristof Provost <kp@FreeBSD.org>
Cc: stable@freebsd.org, freebsd-net@freebsd.org
Subject: Re: ipfw fwd to closed port
Message-ID: <20160609130601.GS75630@zxy.spb.ru>
References: <20160608230240.GA51364@zxy.spb.ru>
 <20160609130017.GA4071@vega.codepro.be>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160609130017.GA4071@vega.codepro.be>
User-Agent: Mutt/1.5.24 (2015-08-30)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: slw@zxy.spb.ru
X-SA-Exim-Scanned: No (on zxy.spb.ru); SAEximRunCond expanded to false
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-net>,
 <mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net/>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-net>,
 <mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 09 Jun 2016 13:06:05 -0000

On Thu, Jun 09, 2016 at 03:00:17PM +0200, Kristof Provost wrote:

> On 2016-06-09 02:02:40 (+0300), Slawa Olhovchenkov <slw@zxy.spb.ru> wrote:
> > Forwarding by ipfw to closed local port generating RST packet with
> > incorrect checksun. Is this know ussuse? Need open PR?
> 
> Where did you capture the packet? If you've captured the packet on the
> machine that generated it tcpdump may indeed claim that the checksum is
> wrong, because it's computed by the hardware (so after tcpdump captured
> it).

On the tun0 (destination of RST packet routed to tun0).
tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1500
        options=80000<LINKSTATE>
        inet 192.168.4.1 --> 192.168.4.1 netmask 0xffffff00 
        inet6 fe80::240:63ff:fedc:ac9e%tun0 prefixlen 64 scopeid 0x9 
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        Opened by PID 1345

tun0 don't computed checksum.