From owner-freebsd-net@FreeBSD.ORG Sat Oct 20 16:59:36 2007 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 450D616A420 for ; Sat, 20 Oct 2007 16:59:36 +0000 (UTC) (envelope-from Hartmut.Brandt@dlr.de) Received: from smtp-1.dlr.de (smtp-1.dlr.de [195.37.61.185]) by mx1.freebsd.org (Postfix) with ESMTP id C9AE813C467 for ; Sat, 20 Oct 2007 16:59:35 +0000 (UTC) (envelope-from Hartmut.Brandt@dlr.de) Received: from knop-beagle.kn.op.dlr.de ([129.247.173.6]) by smtp-1.dlr.de over TLS secured channel with Microsoft SMTPSVC(6.0.3790.1830); Sat, 20 Oct 2007 18:35:17 +0200 Date: Sat, 20 Oct 2007 18:35:17 +0200 (CEST) From: Harti Brandt X-X-Sender: brandt_h@knop-beagle.kn.op.dlr.de To: Len Gross In-Reply-To: <20071019224155.GI20308@server.vk2pj.dyndns.org> Message-ID: <20071020183000.E8153@knop-beagle.kn.op.dlr.de> References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071019224155.GI20308@server.vk2pj.dyndns.org> X-OpenPGP-Key: harti@freebsd.org MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-OriginalArrivalTime: 20 Oct 2007 16:35:17.0350 (UTC) FILETIME=[329F7860:01C81337] Cc: freebsd-net@freebsd.org Subject: Re: Disable Exponential Backoff (retry) on Ethernet? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Harti Brandt List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 20 Oct 2007 16:59:36 -0000 On Sat, 20 Oct 2007, Peter Jeremy wrote: PJ>On Wed, Oct 17, 2007 at 08:51:34PM -0700, Len Gross wrote: PJ>>I'm doing some protocol development and it is convenient to start it on PJ>>Ethernet. I will need to send a packet to the Ethernet device and only have PJ>>it be sent once, even if there is a colision. PJ> PJ>I know we've still got some hubs lying around in a backroom at work PJ>but I don't know of anything that will let you disable the retry-on-CD. PJ> PJ>Have you considered simulating the network at a slightly higher lever: PJ>Use ipfw pipes or similar to simulate packet loss (either set a queue PJ>length of 1 or probabilistically). This could be done either as a PJ>bridge or by tunneling your protocol over IP or UDP. Some years ago I wrote a netgraph node that connected to ethernet nodes and simulated a wireless broadcast channel including collisions, timevariable delay, loss and shaping. Can be done in a couple of hundreds of lines and easily allows >100MBit/sec with gigabit ethernet. The ethernet is just the physical transport medium for the packets and does not take part in the emulation. All that was controlled by bsnmpd and a remote command line tool and/or Java-GUI. Unfortunately I cannot release this (yet) due to licensing... harti