Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!agate!ucbvax!TOMOBIKI-CHO.CAC.WASHINGTON.EDU!mrc
From: mrc@TOMOBIKI-CHO.CAC.WASHINGTON.EDU (Mark Crispin)
Newsgroups: comp.protocols.tcp-ip
Subject: Unix TCP connectivity problems
Message-ID: <MS-C.602280469.662824084.mrc@Tomobiki-Cho.CAC.Washington.EDU>
Date: 31 Jan 89 20:07:49 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 25


     I cannot verify this 100%, but observation suggests that if Unix receives
an ICMP Network Unreachable message it causes select() and/or read() to return
an error.  Most applications programs consider this condition to indicate a
fatal loss of connectivity and they blast the connection away.

     I've observed this problem with SUNs, VAXen, and NeXT machines.

     I've had telnet and rlogin sessions suddenly blow away in the middle of
typein/echoing (with no human-noticable echo delays).  Since Unix doesn't have
the PDP-10 concept of "detached jobs" this means I lose whatever work I was
doing at the time.  I can reconnect back immediately.

     I've seen client/server interactions where the server got the error and
in the course of cleaning up sent a text string that got to the client!

     Can anyone shed any light on this?  What can applications programs do to
protect against this?  Is there a kernel patch that keeps intermittant errors
(a gateway spazz?) from blowing away healthy connections?

     I wish I could provide more details, but until we get our network monitor
I can't say for sure what it is that is biting us.  I know that it hits me
several times a day.

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