Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!ucselx!bionet!ames!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: V3.2 vs V4 UDP and NFS
Message-ID: <93326@sgi.sgi.com>
Date: 23 Mar 91 21:11:26 GMT
References: <16241@uudell.dell.com> <9103160909.AA01947@asylum.sf.ca.us> <17725@sdcc6.ucsd.edu>
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Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <17725@sdcc6.ucsd.edu>, jclark@sdcc6.ucsd.edu (John Clark) writes:
> 
> With UDP and NFS based on it, is there a check sum on the
> reassembled packet. It seems that there is an assumption that the
> ethernet hardware CRC etc. is enough, but is that true.


Many workstation vendors ship with UDP checksums turned on by default.
This provides an end-to-end checksum of the entire NFS/UDP/IP datagram
after reassembly at the destination of any IP fragmentation.

Some customers have strongly held opinions that the CPU cost of computing
the checksum is worthwhile.  On modern hardware, it's hard to disagree.

A major vendor (not my employer, of course!) is said to still be shipping
with UDP checksums off by default.  It is said that a simple adb command
can turn UDP checksums on in recent releases of their software.


Vernon Schryver,   vjs@sgi.com