From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: ppp_generic: fix multilink fragment MTU calculation (again) Date: Tue, 20 Sep 2011 15:21:28 -0400 (EDT) Message-ID: <20110920.152128.1875285861948423018.davem@redhat.com> References: <4E7681BD.2040902@stuffedcow.net> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: v4l@stuffedcow.net Return-path: Received: from mx1.redhat.com ([209.132.183.28]:26339 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194Ab1ITTVd (ORCPT ); Tue, 20 Sep 2011 15:21:33 -0400 In-Reply-To: <4E7681BD.2040902@stuffedcow.net> Sender: netdev-owner@vger.kernel.org List-ID: From: Henry Wong Date: Sun, 18 Sep 2011 19:41:49 -0400 > When using MLPPP, the maximum size of a fragment is incorrectly > calculated with an offset of -2. > This patch reverses the changes in the patch found here: > http://marc.info/?l=linux-netdev&m=123541324010539&w=2 > > The value of hdrlen includes the size of both the 2-byte PPP protocol > field and the 2- or 4-byte multilink header (2+4=6 for long sequence > numbers, 2+2=4 for short sequence numbers). Section 2 of RFC1661 says > that the MRU that is negotiated (i.e., the MTU of the sending system) > includes only the PPP payload but not the protocol field, thus the > correct MTU should be the link's MTU minus the multilink header (mtu - > (hdrlen-2)). > > The incorrect calculation causes Linux to fragment packets to a size > two bytes smaller than the allowed MTU. While not technically illegal, > this behaviour confounds MRU-tuning to avoid PPP-layer fragmentation. > > Signed-off-by: Henry Wong Applied, thanks. There were several cases of trailing whitespace in your patch which I needed to fix up. Please don't be so careless in the future. Thanks.