From mboxrd@z Thu Jan 1 00:00:00 1970 From: Francois Romieu Subject: Re: jme: UDP checksum error, and lots of them Date: Sat, 4 Dec 2010 00:02:50 +0100 Message-ID: <20101203230250.GA3612@electric-eye.fr.zoreil.com> References: <20101201.200935.71110482.davem@davemloft.net> <20101202042820.M98672@cooldavid.org> <20101201.215916.104055114.davem@davemloft.net> <20101202231546.GA3507@electric-eye.fr.zoreil.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , cooldavid@cooldavid.org, netdev@vger.kernel.org To: Jan Engelhardt Return-path: Received: from violet.fr.zoreil.com ([92.243.8.30]:39873 "EHLO violet.fr.zoreil.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752483Ab0LCXDC (ORCPT ); Fri, 3 Dec 2010 18:03:02 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Jan Engelhardt : > On Friday 2010-12-03 00:15, Francois Romieu wrote: > >David Miller : > >[...] > >> Something isn't right here. The only thing that makes sense is if > >> the tcpdump checksum validation is wrong for some reason. Because > >> only then could we give a reason for the UDP frames to not be > >> dropped before vpnc can see them. > > > >Wild guess : 192.168... is the local address and tcpdump chokes on > >an outgoing, yet-not-checksummed packet. > > Then the checksums of all other packets I am emitting would also be 0000 > or wrong, which isn't the case. No. :o) net/ipv4/udp.c::udp4_hwcsum_outgoing provides a packet data length dependent partial checksum and it checksums fragments. -- Ueimor