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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.unix-wizards
Subject: Re: Just how reliable is NFS?
Message-ID: <7180@utzoo.UUCP>
Date: Fri, 3-Oct-86 17:49:22 EDT
Article-I.D.: utzoo.7180
Posted: Fri Oct  3 17:49:22 1986
Date-Received: Fri, 3-Oct-86 17:49:22 EDT
References: <6@cvbnet.uucp> <335@mc0.UUCP> <2428@phri.UUCP> <258@stracs.cs.strath.ac.uk>, <580@celerity.UUCP>
Organization: U of Toronto Zoology
Lines: 18
Keywords: UDP, NFS, checksums

> I would like to point out that the 32-bit CRC generated with every Ethernet
> packet and checked by the receiver of the packet is (orders of magnitude?)
> a far more reliable detector of transmission errors than the artifact of the
> 1st generation of computers, the checksum...

But it does absolutely nothing to detect errors in the Ethernet controller,
the low-level software, and the hardware and software of any gateways
through which the packets pass.  As the Xerox people have been saying for
years, if you want to be sure the data is getting there intact, you put
a checksum (or CRC, or whatever) on it as it leaves the sending application,
and check that checksum when it reaches the receiving application.

Particularly when the "application" is something like NFS, which could make
an incredible mess if packets got garbled, there is something to be said
for such "end-to-end" error checking.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,decvax,pyramid}!utzoo!henry