From owner-freebsd-net@FreeBSD.ORG Tue Oct 28 21:23:51 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 A0E80106567C for ; Tue, 28 Oct 2008 21:23:51 +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 5A2938FC22 for ; Tue, 28 Oct 2008 21:23:51 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (dbbayk1lcggos5zf@localhost.funkthat.com [127.0.0.1]) by hydrogen.funkthat.com (8.13.6/8.13.3) with ESMTP id m9SLNonx028599; Tue, 28 Oct 2008 14:23:50 -0700 (PDT) (envelope-from jmg@hydrogen.funkthat.com) Received: (from jmg@localhost) by hydrogen.funkthat.com (8.13.6/8.13.3/Submit) id m9SLNojV028598; Tue, 28 Oct 2008 14:23:50 -0700 (PDT) (envelope-from jmg) Date: Tue, 28 Oct 2008 14:23:50 -0700 From: John-Mark Gurney To: Nikolay Denev Message-ID: <20081028212350.GF51033@funkthat.com> Mail-Followup-To: Nikolay Denev , Jack Vogel , freebsd-net@freebsd.org References: <2a41acea0810280941g6c9846y6e0d4b8b19313e0a@mail.gmail.com> <84671113-DA04-4EFA-8640-E9AD2F09BB34@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <84671113-DA04-4EFA-8640-E9AD2F09BB34@gmail.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]); Tue, 28 Oct 2008 14:23:51 -0700 (PDT) Cc: freebsd-net@freebsd.org, Jack Vogel Subject: Re: ifconfig em0 mtu 9000 does not update the routing table 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: Tue, 28 Oct 2008 21:23:51 -0000 Nikolay Denev wrote this message on Tue, Oct 28, 2008 at 19:54 +0200: > On 28 Oct, 2008, at 18:41 , Jack Vogel wrote: > > >It can't change the route table when you've given it no address: > > > >IE. ifconfig em0 HOSTNAME mtu 9000 will update it just fine. > > > >Cheers, > > > >Jack > > > > > >On Tue, Oct 28, 2008 at 6:15 AM, Nikolay Denev > >wrote: > >Hello, > > > >As the subject says, I'm trying to enable jumbo frames on running > >machine by setting > >ifconfig em0 mtu 9000 by hand, but nothing changed, and I've fount > >that when I list > >the routing table with the MTU column it shows the connected routes > >still with MTU 1500. > >Is this supposed to work this way? I understand that making ifconfig > >touch the routing table is ugly hack, but maybe the routing code can > >be notified for interface changes by some other mechanism? > > > >btw, this is on 7-STABLE with if_em(4) interfaces. > > > >-- > >Regards, > >Nikolay Denev > > > > > Hi Jack, > > Yes, I understand that, It just looked logical to me to update the > existing entries (directly attached) if no address is given, so one > can use the mtu knob alone. > > Anyways, one rarely touches the mtu alone and this not a real problem, > I've just tried to enable jumbo frames on two running machines with > just the ifconfig em0 mtu 9000 line and wondered why it does not work > for a minute. But what happens if you are talking to a machine that doesn't have jumbo frames enabled? You'd loose communications with the machines if ifconfig auto updated... The real missing part of the puzzle is a daemon that sits around and probes neighbor's MRU size and updates each host route w/ the size that is supported by that host... /me has want to write such a daemon, but the work to do it in C is time consuming. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."