From owner-freebsd-net@FreeBSD.ORG Tue Mar 20 01:47:30 2007 Return-Path: X-Original-To: freebsd-net@freebsd.org 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 50D1716A404 for ; Tue, 20 Mar 2007 01:47:30 +0000 (UTC) (envelope-from bms@FreeBSD.org) Received: from out5.smtp.messagingengine.com (out5.smtp.messagingengine.com [66.111.4.29]) by mx1.freebsd.org (Postfix) with ESMTP id 25E6713C43E for ; Tue, 20 Mar 2007 01:47:30 +0000 (UTC) (envelope-from bms@FreeBSD.org) Received: from out1.internal (unknown [10.202.2.149]) by out1.messagingengine.com (Postfix) with ESMTP id 0D8AA208E13; Mon, 19 Mar 2007 21:47:28 -0400 (EDT) Received: from heartbeat2.messagingengine.com ([10.202.2.161]) by out1.internal (MEProxy); Mon, 19 Mar 2007 21:47:28 -0400 X-Sasl-enc: f57RLV2QVRxes1ZpAwIKb7+k9sSZ8EMJ7wj0VoHt3HTE 1174355250 Received: from [192.168.123.18] (82-35-112-254.cable.ubr07.dals.blueyonder.co.uk [82.35.112.254]) by mail.messagingengine.com (Postfix) with ESMTP id B7C291AB5F; Mon, 19 Mar 2007 21:47:29 -0400 (EDT) Message-ID: <45FF3D2F.3040000@FreeBSD.org> Date: Tue, 20 Mar 2007 01:47:27 +0000 From: "Bruce M. Simpson" User-Agent: Thunderbird 1.5.0.9 (X11/20070125) MIME-Version: 1.0 To: Kevin Lahey References: <994cd1cf0703050842r5e54daa6y5fe6af3083e15cd@mail.gmail.com> <45EC6E88.3080101@tomjudge.com> <20070305115615.W38684@orthanc.ca> <994cd1cf0703052105y375679a4t482f4e35988f9daf@mail.gmail.com> <20070319145422.39bfddcd@yakko.patheticgeek.net> <20070319172156.68cba0a9@yakko.patheticgeek.net> In-Reply-To: <20070319172156.68cba0a9@yakko.patheticgeek.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-net@freebsd.org Subject: Re: PMTU Discovery support 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, 20 Mar 2007 01:47:30 -0000 Kevin Lahey wrote: > > The boxes were running FreeBSD-6.1, but I can't really vouch for the > particular kernel configuration. It could well be that the problem is > with the loose nut behind the wheel, rather than with FreeBSD. :-) > I believe PMTU measurements may only be relied upon for active TCP connections, but it's been a while since I read this code. It would be useful if non-TCP drivers such as gre(4) could be extended to perform PMTU discovery and auto-tune their MTU based on this, as manually setting the MTU is a bit random and can result in horrible fragmentation when going across the big-I Internet. I imagine doing this would require changes to the icmp input path and a bit of abstraction. Regards, BMS