From owner-freebsd-net@FreeBSD.ORG Fri Jul 13 13:09:29 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 5AF8016A405 for ; Fri, 13 Jul 2007 13:09:29 +0000 (UTC) (envelope-from netslists@gmail.com) Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.175]) by mx1.freebsd.org (Postfix) with ESMTP id DEA3113C46B for ; Fri, 13 Jul 2007 13:09:28 +0000 (UTC) (envelope-from netslists@gmail.com) Received: by ug-out-1314.google.com with SMTP id o4so628996uge for ; Fri, 13 Jul 2007 06:09:27 -0700 (PDT) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:user-agent:mime-version:to:cc:subject:references:in-reply-to:content-type:content-transfer-encoding; b=ebvl6urDlnN3ZqH5pwk1rePXD/RM/9gb/1d5472T2/476dSQeyK7A58zHA+qVC0YAd50GplC1TkjfwUw8dsGCVwHYiAYhGLkQmKeqHKF5jsQNK0kBSZJRBkR4JHZE8y0BYoEhEZgmLxGf/CN2WK6nPcAEySJ9IYc3HmGuOKkFL8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:user-agent:mime-version:to:cc:subject:references:in-reply-to:content-type:content-transfer-encoding; b=guZ1XVf1bMMALmPSGU4d3lVj8JsN+JElW7uCl/M6raMNOvb4Hq7mdR694hkONK5MNn/yOoGtXXk3gX5cYcBscFiD77i+brhz1DVAKsw8FeKFVUXdcB6TRCeTpWwvOYBl2ApXy0tZYTMhW1Cyo5ApAXsVU7ftvw/1CPnb3XboyLs= Received: by 10.86.97.7 with SMTP id u7mr1258907fgb.1184330465309; Fri, 13 Jul 2007 05:41:05 -0700 (PDT) Received: from ?192.168.9.8? ( [91.135.49.10]) by mx.google.com with ESMTP id 13sm2964369fks.2007.07.13.05.41.04 (version=SSLv3 cipher=RC4-MD5); Fri, 13 Jul 2007 05:41:04 -0700 (PDT) Message-ID: <469772DA.1000700@gmail.com> Date: Fri, 13 Jul 2007 14:40:58 +0200 From: Sten Daniel Soersdal User-Agent: Thunderbird 2.0.0.4 (Windows/20070604) MIME-Version: 1.0 To: Stephen.Clark@seclark.us References: <46967C5C.5040505@seclark.us> In-Reply-To: <46967C5C.5040505@seclark.us> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-net@freebsd.org Subject: Re: 6.2 mtu now limits size of incomming packet 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: Fri, 13 Jul 2007 13:09:29 -0000 Stephen Clark wrote: > Hello, > > Did something change in 6.2? If my mtu size on rl0 is 1280 it won't > accept a larger incomming packet. > > kernel: rl0: discard oversize frame (ether type 800 flags 3 len 1514 > max > 1294) That is what to be expected. Incoming interface must have mtu set to the same mtu as all other hosts on the same L2 network. If mtu is set to the same as all other hosts, then it is impossible to receive a frame that is too large (assuming everything works). > > I don't think it worked this way in the past. > > Won't this affect pmtud? Incoming interface must have its mtu set to large enough to receive the frame. Outgoing interface, on the other hand, can be lower. For pmtud to work you need to be able to receive packets on an interface with sufficiently set mtu, but the exitting interface can have a lower mtu configured. Thus the router can accept the incoming packet but may drop and notify on a frame that is too large to exit the outgoing interface (assuming DF is set). > > man page for ifconfig says mtu limits size of "transmission" not reception. > > "mtu n Set the maximum transmission unit of the interface to n, > default > is interface specific." Perhaps the man author considered reception to be implied? In any case, enforcing this on incoming packets is correct behavior. -- Sten Daniel Soersdal