From owner-freebsd-current@FreeBSD.ORG Tue Apr 26 09:43:40 2005 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CEDB816A4CE; Tue, 26 Apr 2005 09:43:40 +0000 (GMT) Received: from salmon.maths.tcd.ie (salmon.maths.tcd.ie [134.226.81.11]) by mx1.FreeBSD.org (Postfix) with SMTP id 751B443D5D; Tue, 26 Apr 2005 09:43:39 +0000 (GMT) (envelope-from dwmalone@maths.tcd.ie) Received: from walton.maths.tcd.ie ([134.226.81.10] helo=walton.maths.tcd.ie) by salmon.maths.tcd.ie with SMTP id ; 26 Apr 2005 10:43:38 +0100 (BST) Date: Tue, 26 Apr 2005 10:43:37 +0100 From: David Malone To: Andre Oppermann Message-ID: <20050426094337.GA44893@walton.maths.tcd.ie> References: <20050424150211.GA87520@walton.maths.tcd.ie> <426BC78A.3E56D99B@freebsd.org> <426C1600.106@uq.edu.au> <426D2307.97D15253@freebsd.org> <426D306B.7010000@freebsd.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <426D306B.7010000@freebsd.org> User-Agent: Mutt/1.5.6i Sender: dwmalone@maths.tcd.ie cc: silby@freebsd.org cc: qingli@freebsd.org cc: Matthew Sullivan cc: freebsd-current@freebsd.org Subject: Re: DF (Don't frag) issues X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Apr 2005 09:43:40 -0000 On Mon, Apr 25, 2005 at 08:01:15PM +0200, Andre Oppermann wrote: > - Handling of received ICMP Needfrag messages. The logic was broken > for the cases where the ICMP didn't contain a suggested value. This > brokeness is in there since 5.2R and comes from my cleanup of the > routing table and introduction of TCP hostcache. However there is > no way to fix it at all. It was broken even before I broke it more. > The idea behind the old code was to step down the MTU when we got > a ICMP Needfrag by one step and try again. Unfortunatly it is very > likely that the tcp window was open by a few segments already when > we hit this. This gets us a number of those ICMP's in rapid succession > each stepping us one down. I wonder if we could look into the quoted IP header and extract the length of the IP packet that caused the needs-frag ICMP. That would stop us getting in knots when there are a few packets in flight and would give us a good idea about where we need to step down from. David.