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Date:      Fri, 12 Nov 1999 13:48:15 +0100 (CET)
From:      Micke Josefsson <mj@isy.liu.se>
To:        os2_daemon@altavista.net
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   RE: FreeBSD security on TCP/IP question.
Message-ID:  <XFMail.991112134815.mj@isy.liu.se>
In-Reply-To: <9911120731257C.11943@weba4.iname.net>

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On 12-Nov-99 os2_daemon@altavista.net wrote:
> Hello,
> I've just ran into trouble for mucking around with ifconfig and conflicting
> IP addresses. I'm just an ordinary user without any deep TCP/IP knowledge.
> 
> It all started when curiously, I tried to put 172.16.1.1 which is an NT
> server into ifconfig. Ifconfig said some error messages that the IP address
> have been taken by another machine. Who cares ...

The net cares quite a big deal... Never let two machines have the same IP
address. And don't try to invent your own, the IP address must be in your net's
nameserver to work properly. 
 
> Next day, the sysadmin came to me and accusing me for trying to hijack the
> system. He told me that apparently I crashed his NT by doing so. This brought
> me a very big question. Was he just bluffing, or the NT seriously cannot
> defend against this ?

FreeBSD boxes don't crash from this but the net confusion which is the result
is not good for anyone.  If NT crashes - well, that's exactly what one could
suspect:)

If you can take two boxes off the net and connect them only to each other, then
try all combinations of ifconfig settings on them. It is very informative and
do no harm - as long as they are both disconnected from the internet.

If you don't have FreeBSD on two boxes, you can boot PicoBSD from a floppy and
run it entirely in RAM. I.e. your hard disks won't suffer (unless you mount
them yourself etc)

/Micke

----------------------------------
Michael Josefsson, MSEE
mj@isy.liu.se

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