From owner-freebsd-net@freebsd.org Thu Jun 9 13:16:20 2016 Return-Path: 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 74984B6F407; Thu, 9 Jun 2016 13:16:20 +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 39E8116B4; Thu, 9 Jun 2016 13:16:20 +0000 (UTC) (envelope-from slw@zxy.spb.ru) Received: from slw by zxy.spb.ru with local (Exim 4.86 (FreeBSD)) (envelope-from ) id 1bAzoo-0005ur-9O; Thu, 09 Jun 2016 16:16:18 +0300 Date: Thu, 9 Jun 2016 16:16:18 +0300 From: Slawa Olhovchenkov To: Kristof Provost Cc: stable@freebsd.org, freebsd-net@freebsd.org Subject: Re: ipfw fwd to closed port Message-ID: <20160609131618.GU75630@zxy.spb.ru> References: <20160608230240.GA51364@zxy.spb.ru> <20160609130017.GA4071@vega.codepro.be> <20160609130601.GS75630@zxy.spb.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-SA-Exim-Connect-IP: 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Jun 2016 13:16:20 -0000 On Thu, Jun 09, 2016 at 09:08:33AM -0400, Kristof Provost wrote: > > > On 9 Jun 2016, at 9:06, Slawa Olhovchenkov wrote: > > > On Thu, Jun 09, 2016 at 03:00:17PM +0200, Kristof Provost wrote: > > > >> On 2016-06-09 02:02:40 (+0300), Slawa Olhovchenkov 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 metric 0 mtu 1500 > > options=80000 > > 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 > > Opened by PID 1345 > > > > tun0 don't computed checksum. > > I’m not sure I understand what you’re trying to say. > > In any case: either capture the packet outside the machine, or confirm > that the checksum is wrong by watching the relevant netstat counters. I am have machine with tun0 (see above) and ipfw rules: 04010 23880 2132855 fwd 127.0.0.1,3129 tcp from 192.168.0.0/16 to not me dst-port 80,3128,8080,8100-8105 recv tun0 # netstat -rn 192.168.4.0/24 192.168.4.1 UGS tun0 192.168.4.1 link#9 UH tun0 tun0 handled by coova-chilli. Initator from network 192.168.4.0/24 (ex: 192.168.4.4) send packet to outside, 8.8.8.8 for example. fwd on tun0 forwarded tin 127.0.0.1,3129. No listener on 127.0.0.1:3129, RST generated from 8.8.8.8:80 to 192.168.4.4:2345. This packet routed to tun0 an received by chilli. Checksums must be correct at this point, on tun0 interface for correct handling in chilli.