From owner-freebsd-net@FreeBSD.ORG Tue Aug 20 01:12:56 2013 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 2C3BC51B for ; Tue, 20 Aug 2013 01:12:56 +0000 (UTC) (envelope-from jmg@h2.funkthat.com) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id E50E324C4 for ; Tue, 20 Aug 2013 01:12:55 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id r7K1CtwI037872 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 19 Aug 2013 18:12:55 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id r7K1CsYn037871; Mon, 19 Aug 2013 18:12:54 -0700 (PDT) (envelope-from jmg) Date: Mon, 19 Aug 2013 18:12:54 -0700 From: John-Mark Gurney To: Joe Holden Subject: Re: kern/181388: [route] Routes not updated on mtu change Message-ID: <20130820011254.GZ94127@funkthat.com> Mail-Followup-To: Joe Holden , freebsd-net@freebsd.org References: <201308190700.r7J701I9045665@freefall.freebsd.org> <5211D812.5070308@rewt.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5211D812.5070308@rewt.org.uk> User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 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-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Mon, 19 Aug 2013 18:12:55 -0700 (PDT) Cc: freebsd-net@freebsd.org X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Aug 2013 01:12:56 -0000 Joe Holden wrote this message on Mon, Aug 19, 2013 at 09:32 +0100: > Hm, I hadn't considered that... how do other OSes and vendors handle > this? (eg Linux?) > > Just changing the connected route would probably suffice, or maybe if > any routes not added with default interface mtu could/are be flagged, > then those could be changed or not depending on what added them? How do you know which routes are which? I believe that FreeBSD will automaticly reduce the MTU if you decrease it, but it won't increase it.. How do you know the difference between someone increasing the MTU on the interface to allow a specific host to talk at the larger MTU and wanting the rest of the hosts to talk at the larger MTU... At a previous work place, we used this feature so that we could use MTU 9k to other FreeBSD boxes to get better NFS performance, and but keep the other windows boxes which didn't have MTU 9k compatible interfaces talking on the same LAN... > Perhaps need someone with more experience of the network stack to wade > in here... > > Cheers, > Joe > > On 19/08/2013 08:00, Julian Elischer wrote: > >The following reply was made to PR kern/181388; it has been noted by GNATS. > > > >From: Julian Elischer > >To: bug-followup@FreeBSD.org, joe@rewt.org.uk > >Cc: > >Subject: Re: kern/181388: [route] Routes not updated on mtu change > >Date: Mon, 19 Aug 2013 14:57:22 +0800 > > > > The problem is that this is not as simple as it seems. > > The route MTU MIGHT have been set by something other than the > > interface MTU > > in the first place. > > The interface MTU is a default for the route MTU but is not the only > > source. > > This actuall bit me a couple of days ago when I was wonderign why my > > interface was not sending 9K packets.. turns out you need to do > > 'ifconfig_xn0="DHCP mtu 9000"' in order to have your dncp > > configured interface routes have the right size. > > > > so, I'm agreeing with you , but noticing that there are complications. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."