From owner-freebsd-net@FreeBSD.ORG Wed Oct 29 17:39:09 2008 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 5DA47106568B for ; Wed, 29 Oct 2008 17:39:09 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (gate.funkthat.com [69.17.45.168]) by mx1.freebsd.org (Postfix) with ESMTP id 1AAAC8FC16 for ; Wed, 29 Oct 2008 17:39:09 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (sbd8c3lkz5gj3s1f@localhost.funkthat.com [127.0.0.1]) by hydrogen.funkthat.com (8.13.6/8.13.3) with ESMTP id m9THd8Ye043156; Wed, 29 Oct 2008 10:39:08 -0700 (PDT) (envelope-from jmg@hydrogen.funkthat.com) Received: (from jmg@localhost) by hydrogen.funkthat.com (8.13.6/8.13.3/Submit) id m9THd7ne043155; Wed, 29 Oct 2008 10:39:07 -0700 (PDT) (envelope-from jmg) Date: Wed, 29 Oct 2008 10:39:07 -0700 From: John-Mark Gurney To: Eitan Shefi Message-ID: <20081029173907.GG51033@funkthat.com> Mail-Followup-To: Eitan Shefi , freebsd-net@freebsd.org References: <5D49E7A8952DC44FB38C38FA0D758EADC72E72@mtlexch01.mtl.com> <5D49E7A8952DC44FB38C38FA0D758EADCC5FB7@mtlexch01.mtl.com> <20081028210215.GE51033@funkthat.com> <5D49E7A8952DC44FB38C38FA0D758EADD00926@mtlexch01.mtl.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5D49E7A8952DC44FB38C38FA0D758EADD00926@mtlexch01.mtl.com> User-Agent: Mutt/1.4.2.1i X-Operating-System: FreeBSD 5.4-RELEASE-p6 i386 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (hydrogen.funkthat.com [127.0.0.1]); Wed, 29 Oct 2008 10:39:08 -0700 (PDT) Cc: freebsd-net@freebsd.org Subject: Re: It seems that FreeBSD-7.0 does not use the available MTU X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 29 Oct 2008 17:39:09 -0000 Eitan Shefi wrote this message on Wed, Oct 29, 2008 at 11:34 +0200: > This is indeed the problem, thanks. > > Is this a known issue with FreeBSD-7.0 ? > I do not want to hide a potential bug in the NIC driver. This is a known issue since I fixed the transmit code not to munge the route's MTU so that the route's mtu field would have meaning and allow you to have hosts w/ different MTU's on the network (I've done this in production)... This is definately not a bug in the NIC driver... > -----Original Message----- > From: John-Mark Gurney [mailto:jmg@funkthat.com] > Sent: Tuesday, October 28, 2008 11:02 PM > To: Eitan Shefi > Cc: freebsd-net@freebsd.org > Subject: Re: It seems that FreeBSD-7.0 does not use the available MTU > > Eitan Shefi wrote this message on Mon, Oct 27, 2008 at 23:53 +0200: > > I am using 2 hosts with FreeBSD-7.0 connected directly. > > When I change the MTU to a value greater then 1500, for example 3000, > > and then send "ping" with message size 2500, from one host to the > > other, the other host gets more then one ICMP packet, even thaw the > > message that was send is match smaller then the MTU. > > > > I tried to run this test using a different NIC, but I got the same > > behavior. > > > > I run: > > 1. On both hosts: > > ifconfig mtnic0 mtu 3000 > > 2. Than on one host I run: > > tcpdump -i mtnic0 icmp > > 3. And on the other host I run: > > ping -s 2500 -c 1 OTHER_HOST_IP (ping to "mtnic0" on the other > > host) > > run netstat -rnW to see what the route's MTU is. Most likely you need > to set the mtu before you configure an ip address on the interface so > that the network's route is created w/ the correct MTU... > > either readd the network route, or change the mtu of the route for the > host: > route change -mtu 3000 OTHER_HOST_IP > > also change it on the network route so that when the host route gets > flushed and recreated it will be created w/ the correct MTU... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."