Path: utzoo!mnetor!uunet!husc6!think!ames!pasteur!ucbvax!unisoft!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Checksums, CRC's, and NFS
Message-ID: <4410@hoptoad.uucp>
Date: 11 Apr 88 14:00:09 GMT
References: <8804041338.AA12433@etn-wlv.EATON.COM>
Organization: Grasshopper Group in San Francisco
Lines: 26

mcc@ETN-WLV.EATON.COM (Merton Campbell Crockett) wrote:
> A gut feel is that a VRC/LRC combination for error detection is just as reliable
> as a CRC for detection of errors *and* saves 5 instructions per byte assuming
> the use of a CRC table.  

That would be nice for sending 8-bit data in 9-bit bytes, but we don't have
the vertical check bit except on tapes and other 9-bit media (or when sending
7-bit data).

If people are serious about fixing the checksums (sounds like a good
idea), howabout adding an IP option for full-packet 32 bit CRC?  Any
site could ignore the option, but at least all the ones that used it
would interoperate and check each others' checksums.  The first site,
gateway, or whatever that implemented the option would throw away a
packet whose CRC was bad.

That would not work when passed through gateways which modify the IP
options (e.g. source routing) but don't implement the CRC option.
Another option would be a CRC that protected only the user-data field,
relying on the IP header checksum for the header.  Not as good, but
easier to retrofit.
-- 
{pyramid,pacbell,amdahl,sun,ihnp4}!hoptoad!gnu			  gnu@toad.com
  I forsee a day when there are two kinds of C compilers: standard ones and 
  useful ones ... just like Pascal and Fortran.  Are we making progress yet?
	-- ASC:GUTHERY%slb-test.csnet