From owner-freebsd-net@FreeBSD.ORG Sun Jul 22 07:49:54 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 033BD16A417 for ; Sun, 22 Jul 2007 07:49:54 +0000 (UTC) (envelope-from artem@aws-net.org.ua) Received: from alf.aws-net.org.ua (alf.aws-net.org.ua [85.90.196.192]) by mx1.freebsd.org (Postfix) with ESMTP id 21E2813C45D for ; Sun, 22 Jul 2007 07:49:52 +0000 (UTC) (envelope-from artem@aws-net.org.ua) Received: from [192.168.32.4] (aviko.aws-net.org.ua [192.168.32.4]) by alf.aws-net.org.ua (8.13.8/8.13.8) with ESMTP id l6M7nddk030192 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Sun, 22 Jul 2007 10:49:43 +0300 (EEST) (envelope-from artem@aws-net.org.ua) Message-ID: <46A30C13.1030909@aws-net.org.ua> Date: Sun, 22 Jul 2007 10:49:39 +0300 From: Artyom Viklenko Organization: Art&Co. User-Agent: Thunderbird 2.0.0.5 (Windows/20070716) MIME-Version: 1.0 To: Stephen.Clark@seclark.us 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> <46A2342C.1030205@seclark.us> In-Reply-To: <46A2342C.1030205@seclark.us> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded STARTTLS authentication, not delayed by milter-greylist-3.0 (alf.aws-net.org.ua [192.168.32.253]); Sun, 22 Jul 2007 10:49:44 +0300 (EEST) X-Virus-Scanned: ClamAV version 0.91.1, clamav-milter version 0.91.1 on alf.aws-net.org.ua X-Virus-Status: Clean 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 List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Jul 2007 07:49:54 -0000 Stephen Clark wrote: > 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 > Why? When two endpoints negotiated tcp connections they do know about remote mss - maximum segment that remote side can receive. PMTU is little bit anothr problem of misconfiguration on firewalls and intermediate routers. Very common situation when users block whole ICMP protocol on their router/host while connects to Internet via PPPoE/PPTP. -- Sincerely yours, Artyom Viklenko. ------------------------------------------------------- artem@aws-net.org.ua | http://www.aws-net.org.ua/~artem FreeBSD: The Power to Serve - http://www.freebsd.org