From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: [PATCH] make _minimum_ TCP retransmission timeout configurable Date: Wed, 29 Aug 2007 15:09:58 -0700 Message-ID: <46D5EEB6.3020602@hp.com> References: <200708292052.NAA21975@tardy.cup.hp.com> <5640c7e00708291432q6acde704od52247647a6b453@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Ian McDonald Return-path: Received: from palrel11.hp.com ([156.153.255.246]:60906 "EHLO palrel11.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754640AbXH2WKR (ORCPT ); Wed, 29 Aug 2007 18:10:17 -0400 In-Reply-To: <5640c7e00708291432q6acde704od52247647a6b453@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Ian McDonald wrote: > Hmmm... RFC2988 says: > (2.4) Whenever RTO is computed, if it is less than 1 second then the > RTO SHOULD be rounded up to 1 second. > > Traditionally, TCP implementations use coarse grain clocks to > measure the RTT and trigger the RTO, which imposes a large > minimum value on the RTO. Research suggests that a large > minimum RTO is needed to keep TCP conservative and avoid > spurious retransmissions [AP99]. Therefore, this > specification requires a large minimum RTO as a conservative > approach, while at the same time acknowledging that at some > future point, research may show that a smaller minimum RTO is > acceptable or superior. > > I went and had a look and this RFC has not been obsoleted. RFC3390 > also backs this assertion up. > > So I'm suspecting that the default should be changed to 1000 to match > the RFC which would solve this issue. I note that the RFC is a SHOULD > rather than a MUST. I had a quick look around and not sure why Linux > overrides the RFC on this one. If nothing else, 200 ms is a "principle of least surprise" thing since that is the current value (in MS) for TCP_RTO_MIN. rick jones