From owner-freebsd-hackers Sun Jun 10 18: 3:34 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from whizzo.transsys.com (whizzo.TransSys.COM [144.202.42.10]) by hub.freebsd.org (Postfix) with ESMTP id A60E437B40C; Sun, 10 Jun 2001 18:03:18 -0700 (PDT) (envelope-from louie@whizzo.transsys.com) Received: from whizzo.transsys.com (#6@localhost.transsys.com [127.0.0.1]) by whizzo.transsys.com (8.11.3/8.11.3) with ESMTP id f5B13HI87819; Sun, 10 Jun 2001 21:03:17 -0400 (EDT) (envelope-from louie@whizzo.transsys.com) Message-Id: <200106110103.f5B13HI87819@whizzo.transsys.com> X-Mailer: exmh version 2.3.1 01/18/2001 with nmh-1.0.4 To: Mike Smith Cc: tlambert2@mindspring.com, Bsdguru@aol.com, freebsd-hackers@FreeBSD.ORG X-Image-URL: http://www.transsys.com/louie/images/louie-mail.jpg From: "Louis A. Mamakos" Subject: Re: How to disable software TCP checksumming? References: <200106092135.f59LZW701229@mass.dis.org> In-reply-to: Your message of "Sat, 09 Jun 2001 14:35:32 PDT." <200106092135.f59LZW701229@mass.dis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Sun, 10 Jun 2001 21:03:17 -0400 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 Setting aside the degree to which you choose to be paranoid about where data can be corrupted, and the likelyhood thereof-- there is an architectural issue here, which is that the CRC provided by your friendly neighborhood Ethernet NIC card only protects the data over one Ethernet subnetwork. The TCP checksum, and TCP in general, provides end-to-end semantics, independent of the concatenation of physical links the TCP segments might transit from the source to the destination. If you have an end-to-end protocol, with end-to-end semantics, then you need and end-to-end mechanism. Remember years ago when Sun by default shipped their OS with UDP checksums disabled for UDP-based NFS traffic. The position was that you had this strong 32 bit CRC protecting your NFS traffic between the client and server (on the same LAN, of course) and the UDP checksum was wasteful and degrading performance. And people had mysterious things happen to their files when running UDP/NFS over WAN links and other interesting media and circumstances. Everything old is new again. louie To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message