From owner-freebsd-net@FreeBSD.ORG Fri Dec 22 05:00:59 2006 Return-Path: X-Original-To: freebsd-net@freebsd.org Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id C895E16A407; Fri, 22 Dec 2006 05:00:59 +0000 (UTC) (envelope-from fernando@gont.com.ar) Received: from smtp1.xmundo.net (smtp1.xmundo.net [201.216.232.80]) by mx1.freebsd.org (Postfix) with ESMTP id 8140513C44C; Fri, 22 Dec 2006 05:00:59 +0000 (UTC) (envelope-from fernando@gont.com.ar) Received: from venus.xmundo.net (venus.xmundo.net [201.216.232.56]) by smtp1.xmundo.net (Postfix) with ESMTP id 290C0F0C41B; Fri, 22 Dec 2006 01:31:45 -0300 (ART) Received: from fgont.gont.com.ar (157-184-231-201.fibertel.com.ar [201.231.184.157]) (authenticated bits=0) by venus.xmundo.net (8.12.11.20060308/8.12.11) with ESMTP id kBM4VdkC024975; Fri, 22 Dec 2006 01:31:44 -0300 Message-Id: <7.0.1.0.0.20061220030810.0675daa8@gont.com.ar> X-Mailer: QUALCOMM Windows Eudora Version 7.0.1.0 Date: Wed, 20 Dec 2006 03:12:28 -0300 To: Randall Stewart , "Bruce M. Simpson" From: Fernando Gont In-Reply-To: <4587E869.90108@cisco.com> References: <5628d8010612160452y5c562757h8ef8ed0776c5525d@mail.gmail.com> <458745F8.4090707@FreeBSD.org> <4587E869.90108@cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (venus.xmundo.net [201.216.232.56]); Fri, 22 Dec 2006 01:31:44 -0300 (ART) Cc: freebsd-net@freebsd.org, dave jones Subject: Re: UDP lite for FreeBSD X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 22 Dec 2006 05:00:59 -0000 At 10:26 19/12/2006, Randall Stewart wrote: >I have always thought of it as a bit of a hack as well... and >there is one really big problem with it.. It has no value >unless you can tell your network-interface card to deliver >damaged packets. I don't know if some cards have this option >now or not.. nor if an API in any driver exists for it... without this >you will find very very few packets that are "damaged" that >do get through.. since generally the link layer checksum >is a MUCH better CRC vs the very weak IP/UDP checksum :-0 Each check is meant to detect a different type/source of errors. The CRC is meant to detect burst errors, which are lokely to occur due to, eg, noise. OTOH, the checksum is meant to detect single bit errors, which are more likely to occur in the memory of the processing systems. There'sa paper by Stone and Partridge (in ACM's CCR) in which they show errors that, IIRC, were not caught by the CRC, but *were* caught by the checksum. Kindest regards, -- Fernando Gont e-mail: fernando@gont.com.ar || fgont@acm.org PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1