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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SLIP documents
Message-ID: <1991Feb9.051623.29415@Think.COM>
Date: 9 Feb 91 05:16:23 GMT
References: <4320@ns-mx.uiowa.edu> <1991Feb8.203703.25654@zoo.toronto.edu> <84702@sgi.sgi.com>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 34

In article <84702@sgi.sgi.com> vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes:
>> (For those who don't get the point of the ":-) :-)", NFS uses UDP without
>> checksums.  And people wonder why NFS is so unreliable...)
>Everyone!  Please stop repeating this complaint.  

I agree that the complaint is wrong, but not for the same reason you do.
It isn't NFS that uses unchecksummed UDP, it's SunOS (or maybe BSD Unix) in
general (in its default configuration).  In fact, SunOS doesn't provide a
way for a UDP-based application protocol to control whether it uses
checksums -- it's a single, system-wide parameter.  Even worse, this one
parameter controls both whether checksums are generated during sending and
whether they are checked when receiving.

>Anyone with an NFS implementation that does not use UDP checksums should
>either fix or enjoy it.  The NFS on common and current workstations does
>use UDP checksums by default.  

I think Suns would count as "common and current workstations", and by
default SunOS doesn't enable UDP checksums.  In fact, until SunOS 4.1.1,
enabling UDP checksums required patching the kernel; in the latest release
they've finally moved it into a configuration file used during the kernel
build process.

>				Ours do.  I'm told that Sun's does as
>of the NFS 3.2 source release.

Since the socket library doesn't provide a way to enable or disable UDP
checksums (I could be wrong -- I simply searched for "checksum" in the
setsockopt man page), I don't see how the NFS source release can do this.
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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