From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Heffner Subject: Re: MTU probing bug? Date: Tue, 25 Jul 2006 21:53:01 -0400 Message-ID: <44C6CAFD.8090107@psc.edu> References: <20060725.001744.26930215.davem@davemloft.net> <44C62316.9080501@psc.edu> <20060725.144225.67885911.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org Return-path: Received: from mailer1.psc.edu ([128.182.58.100]:15843 "EHLO mailer1.psc.edu") by vger.kernel.org with ESMTP id S1030352AbWGZBxW (ORCPT ); Tue, 25 Jul 2006 21:53:22 -0400 To: David Miller In-Reply-To: <20060725.144225.67885911.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org David Miller wrote: > I find it interesting that black hole detection is handled > different from a normal probe failure. I guess here we are > dealing with a more significant failure, so we should start > at the thing which is most guarenteed to work. Black hole detection is substantially different than probe failure. It's an indication that your current effective MTU is too large, and must be reduced. A black hole basically means that your current path information is no good, either because your initial values are wrong, or the path changed. So, you really want to reset everything to conservative values. After a failed probe, your effective MTU is still fine, you've just gotten some additional information about the path (that it doesn't support the higher MTU). -John