From owner-freebsd-net@FreeBSD.ORG Thu Dec 13 19:31:53 2012 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 007B154E for ; Thu, 13 Dec 2012 19:31:52 +0000 (UTC) (envelope-from jmg@h2.funkthat.com) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) by mx1.freebsd.org (Postfix) with ESMTP id A8B9B8FC12 for ; Thu, 13 Dec 2012 19:31:52 +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 qBDJVpnS036373 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 13 Dec 2012 11:31:51 -0800 (PST) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id qBDJVprK036372; Thu, 13 Dec 2012 11:31:51 -0800 (PST) (envelope-from jmg) Date: Thu, 13 Dec 2012 11:31:51 -0800 From: John-Mark Gurney To: Zaphod Beeblebrox Subject: Re: ipv6 route ignores MTU. Message-ID: <20121213193151.GE1563@funkthat.com> Mail-Followup-To: Zaphod Beeblebrox , FreeBSD Net References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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]); Thu, 13 Dec 2012 11:31:51 -0800 (PST) Cc: FreeBSD Net 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: Thu, 13 Dec 2012 19:31:53 -0000 Zaphod Beeblebrox wrote this message on Wed, Dec 12, 2012 at 22:50 -0500: > FreeBSD virtual.accountingreality.com 9.1-RC2 FreeBSD 9.1-RC2 #6 r241240: > Sat Oct 6 01:43:35 EDT 2012 > root@virtual.accountingreality.com:/usr/obj/usr/src/sys/VRA > amd64 > > I have set a high MTU: > > em0: flags=8843 metric 0 mtu 9014 > > options=4019b > ether 00:15:17:0d:04:a8 > inet x.y.z.q netmask 0xffffffe0 broadcast x.y.z.q1 > inet6 fe80::215:17ff:fe0d:4a8%em0 prefixlen 64 scopeid 0x5 > inet6 2001:1928:1::52 prefixlen 64 > inet 192.168.221.2 netmask 0xffffff00 broadcast 192.168.221.255 > nd6 options=21 > media: Ethernet autoselect (1000baseT ) > status: active > > curiously, although: > > [1:2:301]root@virtual:~> route -n get 192.168.221.84 > route to: 192.168.221.84 > destination: 192.168.221.0 > mask: 255.255.255.0 > interface: em0 > flags: > recvpipe sendpipe ssthresh rtt,msec mtu weight expire > 0 0 0 0 9014 1 0 > > shows the correct MTU, > > [1:5:304]root@virtual:~> route -n get -inet6 2001:1928:1::84 > route to: 2001:1928:1::84 > destination: 2001:1928:1:: > mask: ffff:ffff:ffff:ffff:: > interface: em0 > flags: > recvpipe sendpipe ssthresh rtt,msec mtu weight expire > 0 0 0 0 1500 1 0 > > shows the wrong MTU. > > The MTU in this case is set in the ifconfig_em0 rc.conf entry and the > machine has been rebooted. Are you sure that the mtu is set before the ipv6 address is assigned to the interface? The route inherits what ever MTU was on the interface when the route was created... It will be clamped if it is lower, but will not be increased... This is so you can set the MTU on a route (say you have a broken low memory device that only accept 512 byte packets) and it will stay the way you set it.. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."