From owner-freebsd-net@FreeBSD.ORG Fri Dec 14 06:05:42 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 3372AC09 for ; Fri, 14 Dec 2012 06:05:42 +0000 (UTC) (envelope-from zbeeble@gmail.com) Received: from mail-lb0-f182.google.com (mail-lb0-f182.google.com [209.85.217.182]) by mx1.freebsd.org (Postfix) with ESMTP id 9A4548FC16 for ; Fri, 14 Dec 2012 06:05:41 +0000 (UTC) Received: by mail-lb0-f182.google.com with SMTP id go10so2463992lbb.13 for ; Thu, 13 Dec 2012 22:05:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=nw0jJBDBrqpOLMFX/ltKMLD9d4jkNt7ffaIhZi/E2ag=; b=ju2UVH2yfOVg14Fd55+cqaAp/JTBHUC9cfpUemzAGemyufsdqUKkXGK06x5b7TnOuO vE4AbKdWaEOR5xtNtpP4P58u4tyNtv2GVbI5um3Qya11I1ly2nV3i6f5PIKI2+Q4ZSwC cneuAAqBX2XcdDAaBGj0TsdSP3JrczWjY8eq+gDVi5LrUHq6zcc2OLnSAiCjwQeFomah LwlvN8oUCGrZlqFhX/gkqjmMyzniYWz98DST/kotI8ZZm630QLG8kpK+S00w2MhKPW/O C/rjucaXJB73MlXBD8qkJVcUt7MMu4BW5YZPEad2pEFbvxc0ACTn90P0vvi7zRhO//fZ Xb5Q== MIME-Version: 1.0 Received: by 10.112.26.41 with SMTP id i9mr1875206lbg.77.1355465140118; Thu, 13 Dec 2012 22:05:40 -0800 (PST) Received: by 10.112.61.33 with HTTP; Thu, 13 Dec 2012 22:05:39 -0800 (PST) In-Reply-To: <20121213193151.GE1563@funkthat.com> References: <20121213193151.GE1563@funkthat.com> Date: Fri, 14 Dec 2012 01:05:39 -0500 Message-ID: Subject: Re: ipv6 route ignores MTU. From: Zaphod Beeblebrox To: Zaphod Beeblebrox , FreeBSD Net Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 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: Fri, 14 Dec 2012 06:05:42 -0000 On Thu, Dec 13, 2012 at 2:31 PM, John-Mark Gurney wrote: > > 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.. Ordinarily, I would expect that since the MTU setting is in the ifconfig_em0 configuration line, this was sufficient. However, I realize now that this is not the case. Putting the MTU into the ipv6_ifconfig line did the trick. This is a rather serious violation of POLA --- I would suggest that some thought should be given to how this is configured and documented.