Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!eecae!netnews.upenn.edu!rutgers!cmcl2!adm!xadmx!ted@nmsu.edu
From: ted@nmsu.edu
Newsgroups: comp.unix.wizards
Subject: arp strangeness
Message-ID: <18308@adm.BRL.MIL>
Date: 3 Feb 89 20:44:14 GMT
Sender: news@adm.BRL.MIL
Lines: 19


This may or may not belong on this group, but it does strongly affect
most unix systems (esp those on the internet).

The basic question is, on a class b network (128.123.x.x), what SHOULD
happen when some host pings 128.123.255.255 (local broadcast).
Obviously, ping may or may not realize that this address is a
broadcast address.  If it does not, then it will originate an arp
request for the broadcast address which is the source of the real rub.
What should host x do when it receives an arp request for broadcast?

As a hint of what perhaps should not happen, in our situation, the
final result is that several Ungermann Bass terminal servers decide
that they are the broadcast address in question and they return an arp
response with their own ethernet address with equated with the ip
broadcast address.  It is very hard to follow exactly what is cause
and what is effect in the amazing storm that succeeds the anomalous
request and so it is hard to determine exactly what is happening and
why.