Date: Thu, 27 Sep 2001 10:35:36 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: "Louis A. Mamakos" <louie@TransSys.COM> Cc: Ronald G Minnich <rminnich@lanl.gov>, hackers@FreeBSD.ORG Subject: Re: TCP&IP cksum offload on FreeBSD 4.2 Message-ID: <15283.14648.430630.163513@grasshopper.cs.duke.edu> In-Reply-To: <200109271416.f8REGaZ64624@whizzo.transsys.com> References: <Pine.LNX.4.33.0109270728220.26552-100000@snaresland.acl.lanl.gov> <200109271416.f8REGaZ64624@whizzo.transsys.com>
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Louis A. Mamakos writes: > The other type of failure you might not catch are software errors; that > is, where a packet is produced by the network stack and then is > subsequently stomped on by a random store from some other code. Or > a mis-programmed I/O card with scatter/gather capability doesn't pick > up what was intended, etc. The Internet checksum is useful for > detecting this class of error. > No, you're missing the point almost entirely. The checksum is not skipped. It is calculated by the DMA engine based on the data that's transferred across the I/O bus on the receiver (and / or the sender). If the data is incorrect as seen by the receiving nic, the checksum will be wrong and the packet will be dropped. If the packet lands in the wrong place, you have much worse problems. Drew To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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