From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: UDP path MTU discovery Date: Mon, 29 Mar 2010 14:01:04 -0700 Message-ID: <4BB11510.9000302@hp.com> References: <1269561751.2891.8.camel@ilion> <877how25kx.fsf@basil.nowhere.org> <4BB0DCF6.9020401@hp.com> <20100329201431.GH20695@one.firstfloor.org> <20100329205035.GA32656@laped.iglesias.mooo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Glen Turner , netdev@vger.kernel.org To: "Edgar E. Iglesias" Return-path: Received: from g5t0006.atlanta.hp.com ([15.192.0.43]:34399 "EHLO g5t0006.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753051Ab0C2VBI (ORCPT ); Mon, 29 Mar 2010 17:01:08 -0400 In-Reply-To: <20100329205035.GA32656@laped.iglesias.mooo.com> Sender: netdev-owner@vger.kernel.org List-ID: > Are things really that bad? > > These "transactional" IPv6 apps all have the option to stick to 1280 > sized datagrams to avoid the problem. If throughput is an issue these > apps will surely benefit from proper PMTUD anyway or? I would get the alphabet soup completely garbled, but the DNS folks are talking about EDNS (?) message sizes upwards of 4096 bytes - encryption/authentication and other angels being asked to dance on the head of the DNS pin are asking for more and more space in the messages. So, someone will have to blink somewhere - either DNS will have to go TCP and *possibly* take RTT hits there depending on various patch streams, or the IEEE will have to sanction jumbo frames and people deploy them widely, or it will have to become feasible to actually do the occasional IPv6 datagram fragmentation and get a timely retransmission out of a UDP application on a PMTU hit. rick jones