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Date:      Mon, 23 Mar 2009 15:32:08 -0500
From:      David Kelly <>
To:        John Almberg <>
Subject:   Re: utility that scans lan for client?
Message-ID:  <>
In-Reply-To: <>
References:  <> <> <>

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On Mon, Mar 23, 2009 at 03:41:55PM -0400, John Almberg wrote:
> On Mar 23, 2009, at 3:19 PM, David Kelly wrote:
> >How about something as simple as "arp -a"? This lists the arp cache
> >of machines recently heard by your machine. If you know the IP
> >address of the machine in question and its not in your arp table,
> >ping it.  Then the MAC address will appear unless there is a router
> >between here and  there.
> H'mmm. This is also very interesting.
> nmap did not find this appliance, as it turns out. But arp -a did  
> found something on (see below)
> server1 ( at 0:13:d4:45:45:31 on en1 [ethernet]
> server2 ( at (incomplete) on en1 [ethernet]
> server3 ( at 0:23:12:f8:5e:fd on en1 [ethernet]
> I'm guessing this appliance (a Vonage phone adapter) is doing  
> something non-standard.

No, its just ignoring pings. An incomplete entry in the ARP table says
your machine tried to look up that address, creating an entry, but as of
the moment the table was read the reply had not yet come back.

Whatever router you are using is sure to have the Vonnage appliance in
its ARP table.

"Smart" network switches prevent your FreeBSD host from eavesdropping on
the ARP packet exchange between Vonnage and router. Otherwise it would
be in the arp table if the Vonnage has spoken recently to the router.

David Kelly N4HHE,
Whom computers would destroy, they must first drive mad.

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