From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: UDP path MTU discovery Date: Sun, 28 Mar 2010 10:41:37 +0200 Message-ID: <87bpe825z2.fsf@basil.nowhere.org> References: <1269561751.2891.8.camel@ilion> <20100325.202424.201654947.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: gdt@gdt.id.au, netdev@vger.kernel.org To: David Miller Return-path: Received: from one.firstfloor.org ([213.235.205.2]:48829 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753789Ab0C1Ilo (ORCPT ); Sun, 28 Mar 2010 04:41:44 -0400 In-Reply-To: <20100325.202424.201654947.davem@davemloft.net> (David Miller's message of "Thu, 25 Mar 2010 20:24:24 -0700 (PDT)") Sender: netdev-owner@vger.kernel.org List-ID: David Miller writes: > From: Glen Turner > Date: Fri, 26 Mar 2010 10:32:31 +1030 > >> This differs from TCP, where it is the kernel -- and not >> the application -- which organises retransmission. On >> receiving a ICMP Fragmentation Needed the kernel can >> immediately re-probe the path MTU wiht no waiting for >> an exponential timer to expire. > > So the argument is, the kernel TCP does retransmission smart, > userspace UDP apps do it stupidly, so let's turn off the feature > instead of fixing userspace. > > Right? > > Sorry, fix this correctly in the user apps. Putting the > blame on UDP path MTU discovery is placing it in the > wrong spot. It means though that all IPv6 UDP applications essentially have to implement path mtu discovery support (which is non trivial) Will be likely a long time until they're all fixed. Seems like a big hole not considered by the IPv6 designers? -Andi -- ak@linux.intel.com -- Speaking for myself only.