From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Yongjun Subject: Re: [PATCH] Fix bug of update IPv4 PMTU when received ICMP Fragmentation Needed message Date: Mon, 04 Jun 2007 12:03:57 +0800 Message-ID: <46638F2D.90608@cn.fujitsu.com> References: <46635F39.2090009@cn.fujitsu.com> <20070604025528.GA27750@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Herbert Xu Return-path: Received: from [222.73.24.84] ([222.73.24.84]:62193 "EHLO song.cn.fujitsu.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751357AbXFDEKK (ORCPT ); Mon, 4 Jun 2007 00:10:10 -0400 In-Reply-To: <20070604025528.GA27750@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org > On Mon, Jun 04, 2007 at 08:39:21AM +0800, Wei Yongjun wrote: > >>> Huh? The test new_mtu >= old_mtu should only hold if the sending router >>> is buggy which is what the hack is for. >>> >> Note here old_mtu is not the real old mtu, is the received message's size: >> unsigned short old_mtu = ntohs(iph->tot_len); >> So maybe the patch would like following. >> > > The size of the packet that caused the ICMP is what we want here. That's > why the router must be buggy. > > So I want to know how the route announce a MTU larger then 576, such as 1280? RFC says ICMP error message return as much as we can without exceeding 576 bytes. And ipv4 router alaways return as a packet size 576 because of this. If MTU is greater then 576, HOST will used "mtu = guess_mtu(old_mtu)" to get a MTU. Method of send ICMP Fragmentation Needed message is difference from receive, how can this resolve? Change the method of send ICMP Fragmentation Needed message? I do not think so, the only think we can do is to change the method of receive ICMP message. Do you agree this? -- A new email address of FJWAN is launched from Apr.1 2007. The updated address is: yjwei@cn.fujitsu.com -------------------------------------------------- Wei Yongjun Development Dept.I Nanjing Fujitsu Nanda Software Tech. Co., Ltd.(FNST) 8/F., Civil Defense Building, No.189 Guangzhou Road, Nanjing, 210029, China TEL: +86+25-86630523-858 COINS: 79955-858 FAX: +86+25-83317685 MAIL: yjwei@cn.fujitsu.com --------------------------------------------------