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Path: utzoo!mnetor!seismo!uwvax!dave
From: dave@rsch.wisc.edu (Dave Cohrs)
Newsgroups: net.unix-wizards
Subject: Re: Just how reliable is NFS?
Message-ID: <2677@rsch.WISC.EDU>
Date: Tue, 9-Sep-86 17:25:20 EDT
Article-I.D.: rsch.2677
Posted: Tue Sep  9 17:25:20 1986
Date-Received: Thu, 11-Sep-86 22:45:14 EDT
References: <6@cvbnet.uucp> <335@mc0.UUCP> <2428@phri.UUCP>
Sender: news@rsch.WISC.EDU
Reply-To: dave@rsch.wisc.edu (Dave Cohrs)
Organization: U of Wisconsin CS Dept
Lines: 33
Keywords: UDP, NFS, checksums
Summary: No checksums on UDP causes problems

We are running kernels on our vaxen with NFS code, which means the
UDP checksums are off.

I haven't seen any problems with NFS because of this, however, the
lack of checksums does cause problems with rwho.

One of our networks is a Proteon 10 Mbit Pronet.

[ Note-- I refuse to blame Proteon for the extent of our problems.  I am
  positive that the low quality cables we use are causing our problems. ]

Every once in a while, the network flakes out and lots of bad packets
get generated.  The proteon boards are supposed to have a checksum
built in that catches single and double bit errors, but these packets
have lots of errors.  When UDP gets the packets, it just passes them
up to rwho.

Well, rwho gets the packets and checks to make sure the hostname is
all printable ASCII.  This is reasonable, but, often, the errors
causes the letters to change case or to become different printable
ASCII characters.

This leads to some pretty strange host lists when one runs 'ruptime'.

I have also seen this kind of mangled rwho packet on one of our
Ethernets, but, once again, I haven't seen the lack of checksums
affecting NFS.

--
Dave Cohrs
(608) 262-1204
..!{harvard,ihnp4,seismo,topaz}!uwvax!dave
dave@rsch.wisc.edu