Date: Sat, 21 Jul 2007 12:28:28 -0400 From: Stephen Clark <Stephen.Clark@seclark.us> To: Artyom Viklenko <artem@aws-net.org.ua> Cc: freebsd-net@freebsd.org, Artem Belevich <fbsdlist@src.cx>, Julian Elischer <julian@elischer.org> Subject: Re: 6.2 mtu now limits size of incomming packet Message-ID: <46A2342C.1030205@seclark.us> In-Reply-To: <46A1BDDE.5080403@aws-net.org.ua> References: <200707150237.l6F2bAgZ011098@redrock.karels.net> <469E0FFF.8070802@seclark.us> <20070720172021.8EA3D13C4B3@mx1.freebsd.org> <46A10063.9010902@elischer.org> <46A10860.50804@es.net> <ed91d4a80707201534q6e32a9c5j8803ec96fa7f6515@mail.gmail.com> <46A1BDDE.5080403@aws-net.org.ua>
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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)
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