From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kristof Provost Subject: Re: TCP checksum error on local device Date: Wed, 9 Jul 2008 15:10:20 +0000 Message-ID: <20080709151019.GG27741@nereid> References: <9a6873fa0807090734ge7ef12lf09e78db44ba77f5@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Kevin Spiteri Return-path: Received: from rhineheart.priorweb.be ([213.193.229.215]:56183 "HELO rhineheart.priorweb.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1759960AbYGIPGh (ORCPT ); Wed, 9 Jul 2008 11:06:37 -0400 Content-Disposition: inline In-Reply-To: <9a6873fa0807090734ge7ef12lf09e78db44ba77f5@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2008-07-09 16:34:32 (+0200), Kevin Spiteri wrote: > When I send TCP data from localhost to localhost (either on 127.0.0.1 > or on the public IP of the machine), the TCP checksum is wrong. > I suspect this is intended and expected behaviour. The checksum is quite useless as the packet never travels over the network and can't be corrupted. The transmit code in net/ipv4/ip_output.c seems to mark packets for the loopback interface with CHECKSUM_UNNECESSARY. I guess the connection over loopback still carries the data like you'd expect right? Kristof