Xref: utzoo comp.protocols.tcp-ip.ibmpc:3803 comp.protocols.tcp-ip:13098
Path: utzoo!attcan!uunet!bu.edu!rpi!dali.cs.montana.edu!milton!Tomobiki-Cho!mrc
From: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Newsgroups: comp.protocols.tcp-ip.ibmpc,comp.protocols.tcp-ip
Subject: Re: Ungermann-Bass ICMP problems
Keywords: Ungermann-Bass, ICMP
Message-ID: <7894@milton.u.washington.edu>
Date: 20 Sep 90 21:59:40 GMT
References: <29878@netnews.upenn.edu>
Sender: news@milton.u.washington.edu
Organization: Mendou Zaibatsu, Tomobiki-Cho, Butsumetsu-Shi
Lines: 28

In article <29878@netnews.upenn.edu> litwack@dccs.upenn.edu (Mark Litwack) writes:
>It's taken me a while to finally figure this out, but
>it seems that Ungermann-Bass PC-NIU/ex cards occasionally
>send out an ICMP host unreachable message to a host that's
>sending too much TCP data to another host on the local
>ethernet.  This has the effect of severing the TCP connection
>between the two innocent hosts.

This is a bug in 4.x BSD TCP.  It causes all blocked open(), read(),
and write() calls to fail with an error when an ICMP Destination Host
(or Network) Unreachable is received.

A quick fix is to patch out the entries at inetctlerrmap+8.  The right
fix is to fix it so only open()'s are nailed.

>I also found that while Ultrix systems cause the TCP application
>to bomb out when it receives the packet, Suns are not affected.
>I guess they have some kind of sanity check for ICMP messages.

I suspect SUNs have this or a similar bugfix.  So do NeXT's.

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