From owner-freebsd-hackers Fri Jun 8 9:41:39 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from prism.flugsvamp.com (cb58709-a.mdsn1.wi.home.com [24.17.241.9]) by hub.freebsd.org (Postfix) with ESMTP id 0732C37B405 for ; Fri, 8 Jun 2001 09:41:36 -0700 (PDT) (envelope-from jlemon@flugsvamp.com) Received: (from jlemon@localhost) by prism.flugsvamp.com (8.11.0/8.11.0) id f58Geqr63121; Fri, 8 Jun 2001 11:40:52 -0500 (CDT) (envelope-from jlemon) Date: Fri, 8 Jun 2001 11:40:52 -0500 (CDT) From: Jonathan Lemon Message-Id: <200106081640.f58Geqr63121@prism.flugsvamp.com> To: Bsdguru@aol.com, hackers@freebsd.org Subject: Re: How to disable software TCP checksumming? X-Newsgroups: local.mail.freebsd-hackers In-Reply-To: Organization: Cc: Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In article you write: >This thread is baffling. The bottom line is that you cant trust data coming >into your machine, and you have to checksum it. The link level check only >verifies that what was sent by the last forwarding point is the same as what >you got, but in NO WAY implies that all of the data is valid. A link level >checksum pass is a necessary, but not a sufficient condition for the data >being acceptable. There are scads of reasons that it could be bad. Disabling >checksumming is a kludge that you may chose to do, but its never the right >thing to do. I think there's some confusion here. There are two types of checksums: 1. CRC link-level checksum on the ethernet packet. 2. Upper layer checksums (TCP/IP) All hardware that I'm aware of automatically performs #1, I'm not sure if there is anything that will permit disabling this. Step 2 is usually known as the "end-to-end" checksum, and is traditionally performed by the host CPU. Depending on your view of what constitutes an "endpoint", these checksums may be performed by the network adapter itself. I believe that this is what the original meant by disabling software checksums, in the sense that his hardware would do this work. Dispensing with TCP/IP checksum altogether is a fairly bad idea, but I don't think that is what was being proposed here. -- Jonathan To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message