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Date: Sun, 03 Jan 2010 18:02:13 -0800
From: perryh@pluto.rain.com
To: yuri@rawbw.com, glen.j.barber@gmail.com
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Cc: freebsd-hackers@freebsd.org
Subject: Re: Does FreeBSD issue messages about MAC/IP conflicts?
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Glen Barber <glen.j.barber@gmail.com> wrote:
> On Sun, Jan 3, 2010 at 6:40 PM, Yuri <yuri@rawbw.com> wrote:
> > I accidentally had two machines having the same wifi MAC
> > address.  Wifi router gave them both the same local IP address
> > and they both could somewhat connect to the outside world, but
> > connections were flaky.
> >
> > No messages about IP/MAC conflicts appeared in dmesg log.
> >
> > Vague memories from the long ago past remind me that Windows
> > was issuing IP conflict messages in the local wired network.
> >
> > Why doesn't FreeBSD complain at leat about the IP conflict?
>
> The last time I made the mistake of having two devices with the
> same IP, I saw ARP messages in /var/log/messages as well as the
> system console.  This was around 8.0-RC1, for what it's worth.

ARP will notice when two different MAC addresses both claim the same
IP address, but to detect two different boxes both claiming the same
MAC/IP address pair would require some other way of identifying the
two boxes as different.