From owner-freebsd-net@FreeBSD.ORG Sat Jul 21 16:28:31 2007 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 9F68316A417 for ; Sat, 21 Jul 2007 16:28:31 +0000 (UTC) (envelope-from Stephen.Clark@seclark.us) Received: from smtpout09.prod.mesa1.secureserver.net (smtpout09-04.prod.mesa1.secureserver.net [64.202.165.17]) by mx1.freebsd.org (Postfix) with SMTP id 679AA13C480 for ; Sat, 21 Jul 2007 16:28:31 +0000 (UTC) (envelope-from Stephen.Clark@seclark.us) Received: (qmail 2359 invoked from network); 21 Jul 2007 16:28:29 -0000 Received: from unknown (24.144.77.243) by smtpout09-04.prod.mesa1.secureserver.net (64.202.165.17) with ESMTP; 21 Jul 2007 16:28:29 -0000 Message-ID: <46A2342C.1030205@seclark.us> Date: Sat, 21 Jul 2007 12:28:28 -0400 From: Stephen Clark User-Agent: Mozilla/5.0 (X11; U; Linux 2.2.16-22smp i686; en-US; m18) Gecko/20010110 Netscape6/6.5 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Artyom Viklenko References: <200707150237.l6F2bAgZ011098@redrock.karels.net> <469E0FFF.8070802@seclark.us> <20070720172021.8EA3D13C4B3@mx1.freebsd.org> <46A10063.9010902@elischer.org> <46A10860.50804@es.net> <46A1BDDE.5080403@aws-net.org.ua> In-Reply-To: <46A1BDDE.5080403@aws-net.org.ua> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-net@freebsd.org, Artem Belevich , Julian Elischer 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 Reply-To: Stephen.Clark@seclark.us List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 21 Jul 2007 16:28:31 -0000 Artyom Viklenko wrote: >Artem Belevich wrote: > > >>Here's one example where MTU!=MRU would be useful. >> >>Think of asymmetric bandwith-limited ADSL links. Lower MTU would allow >>lower TX latency for high priority packets when upstream is saturated, >>yet large MRU on the downstream would be great for downloads. >> >>Right now with 6.2 one has to trade off lower latency for faster download. >> >>--Artem >> >> > >You can prioritize small packets with ACKs, for example, by other >techniques - ALTQ one of them. >Unconditional lovering MTU even on ADSL tend to loss throughtput. > >And let's think about TCP MSS. When TCP connection establishes, >TCP stack uses MTU as measure to choose MSS. > >Any two hosts, connected to single Layer2 network MUST use >same MTU. Any other cases lead to hard-to-solve problems. > >This is all IMHO. But I would not like to see different >MTU and MRU on my Ethernet interfaces! :) > > > Yes but the mss is what the endpoints in the connection know about their own mtu's, at this point there is no knowledge of the mtu/mru's of intermediate routers. Steve -- "They that give up essential liberty to obtain temporary safety, deserve neither liberty nor safety." (Ben Franklin) "The course of history shows that as a government grows, liberty decreases." (Thomas Jefferson)