I have an NT network using DHCP with about 50 computers attached. Most
computers get their ip address via dhcp; a few have static addresses.
One with a static address is the NT server with an address of
192.168.1.100. For the past couple of months, a message pops up on the
NT server every couple of days saying that 192.168.1.100 is having an
ip address conflict with a device that has the mac address
00:12:F0:3A:8F:E2. I have not been able to find a way to identify the
device with this mac address. Any ideas??

Try downloading Advanced IP Scanner from
http://www.radmin.com/radmin/utility/index.php - it will scan the
network, and then you can order the results by IP address.

Do this with the server powered off.

THen once you've got the IP address, right click on it and choose to
get all the info. It'll deep scan that machine, and give you more
details. But I expect that the machine name alone will be sufficient?

Here's another free tool where you can type in the MAC address, and it
will show you all of the IP addresss, and the PC name that has that IP
address.

http://www.youngzsoft.net/cc-get-mac-address/

Hopefully you have a full inventory of your 50 PCs, and then you will
know exactly where the conflict lies, by using this tool.  You can
then goto the conflicting PC and change it - either to another static
IP or change it to dynamic.

Brady

I don't know if it will help, but the MAC address indicates it is an
Intel network card.

If you haven't named and made a list of all of your PCs the above
suggestions won't help you (although if you have they are excellent
suggestions). If your network is built using managed switches or hubs
the management software should have some way of displaying the MAC
addresses of connected equipment, and that will show you what port the
machine is connected to. If the network gear is unmanaged you could
try "pinging" the machine continuously and disconnecting machines at
the patch panel until you find the port that disconnects it and the
pings fail.

Just another thought - while you mention 50 computers, don't forget
that a lot of other devices have IP addresses as well (routers,
managed switches/hubs, printers etc).

The best way I would approach this is to use the command "ARP -A" this
will give you a list of all the devices within your network that have
established connectivity together with their mac addresses.  You can
then check the ip address that corresponds to the mac address which is
indicated as conflicting.

Moreover, I would make sure that the DHCP address pool does not
include the 192.168.1.100, which is used by your NT server. Just
exclude that address from your pool if it is....

there is a protocol called ARP,it stands for Address Resolution
Protocol.tis is the protocol at the physical link layer of the OSI
model ehich helps in resolving ip addresses with corresponding MAC
address,so for ur conflict u please try working with RARP reverse ARP
urproblem might solve.type arp -a to get full details.
Thanks and Regards

If the device is actually allowed to secure 192.168.1.100, pull the
network cable from the server and from a different PC, issue an
NBTSTAT -A 192.168.1.100. This will dump the PC name, currrently
logged in user and domain. If there is no user currently logged in,
net use to the C$ sharepoint on the machine and browse to the 
Documents and Settings folder and see whose ID is in there. NET USE T:
\\computername\c$

Because it is just an occasional error, I would suspect a laptop
(maybe someone who is only in once in a while like a salesperson, or
another traveler). You may want to make sure that .100 is excluded
from your DHCP range and expire all of your leases. I would however
suspect that it is a user with a static IP address on the computer,
probably setup to access a home router. Since it is not uncommon for
home routers to use a 192.168.x.x range, it would be good practice to
user 10.x.x.x address for businesses to eliminate this possibility as
home networks become more popular.