From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267632AbUHVW6j (ORCPT ); Sun, 22 Aug 2004 18:58:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267650AbUHVW6j (ORCPT ); Sun, 22 Aug 2004 18:58:39 -0400 Received: from dspnet.fr.eu.org ([62.73.5.179]:30471 "EHLO dspnet.fr.eu.org") by vger.kernel.org with ESMTP id S267632AbUHVW6g (ORCPT ); Sun, 22 Aug 2004 18:58:36 -0400 Date: Mon, 23 Aug 2004 00:58:33 +0200 From: Olivier Galibert To: linux-kernel@vger.kernel.org Subject: Re: Cursed Checksums Message-ID: <20040822225833.GA5225@dspnet.fr.eu.org> Mail-Followup-To: Olivier Galibert , linux-kernel@vger.kernel.org References: <1093174820.24319.60.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 22, 2004 at 11:03:54PM +0200, Josan Kadett wrote: > Perhaps there is a way to recompute IP header checksums before they get into > the interface? As I outlined, I have found a way to manipulate IP source > address before the packet is flushed to system, but a means of recalculating > the IP header checksum after that manipulation should be found. Because even > if I ignore IP header CRC in one system, all other boxes connected to this > machine has to be patched the same. That is impossible anyway. > > Only if I could find a way to recalculate the checksum in IP headers by > doing a simple hack to the kernel, everything would be alright. Why don't you patch the checksum when you change the IP? It's just a not of the sum the 16-bit words so take the old one, not it, add the two 16-bits differences, re-not it and write it back. OG.