From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [PATCH] l2tp: avoid checksum offload for fragmented packets Date: Mon, 3 Jun 2013 15:44:12 +0100 Message-ID: <1370270652.1918.14.camel@bwh-desktop.uk.level5networks.com> References: <1370245762-5126-1-git-send-email-tparkin@katalix.com> <1370245762-5126-2-git-send-email-tparkin@katalix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , To: Tom Parkin Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:37872 "EHLO webmail.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752229Ab3FCOoP (ORCPT ); Mon, 3 Jun 2013 10:44:15 -0400 In-Reply-To: <1370245762-5126-2-git-send-email-tparkin@katalix.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2013-06-03 at 08:49 +0100, Tom Parkin wrote: > Hardware offload for UDP datagram checksum calculation doesn't work with > fragmented IP packets -- the device will note the fragmentation and leave the > UDP checksum well alone. > > As such, if we expect the L2TP packet to be fragmented by the IP layer we need > to perform the UDP checksum ourselves in software (ref: net/ipv4/udp.c). > > This change modifies the L2TP xmit path to fallback to software checksum > calculation if the L2TP packet + IP header exceeds the tunnel device MTU. [...] Surely this should be done in the IP stack when fragmenting, not in any particular client? Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.