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MAC address

Posted on 2011-02-17
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Last Modified: 2012-05-11
I'm getting a ip conflict on the network, and when I look at the event logs it shows the MAC of the computer that it is conflicting with. I do a network scan that MAC never shows up. The scan sees all the computers and printers and their MAC but this one MAC in the event log never shows. I have not clue where it's coming from. Even when I look at the connection systems in the router this MAC still doesn't show. Any ideas?
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Question by:timgreen7077
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by:snurker
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There are tons of items that could have IP addresses, all with MAC addresses. Switches, routers, Virtual Machines. This happens often with Virtual Machines because they are often clones of another machine.

You can try turing off the one PC that you know has the IP and then attempt to navigate to the otehr device through web or SMB.

To resolve this, you may need to increase the size of your scope on DHCP or if it is static, you will need to reserve this IP for your system. Highly recommend leaving static IPs out of the scope. Reservations work, but it is easier to just not have them as part of the scope.
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by:timgreen7077
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Scope is from 100 to 254. We only use about 30% of this. All static IPs are below this scope.
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by:Sommerblink
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To help with your search, I use http://standards.ieee.org/develop/regauth/oui/public.html to ferret out at least the manufacture of the NIC... sometimes this has no bearing on actual manufactuer of the device... but it may help.
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by:snurker
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Did you verify that there are no Virtual machines on the network? Also if it is using a standard IP range like 192.168.1.X or 0.X, you could have added a device that has a static IP like a router to the network. I have seen people do this and use the router as a switch by their pc in order to add another device or pc.
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by:timgreen7077
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I have a virtual machine but it's on my PC. I even checked that and it uses a different MAC. Yes it's using a standard IP range. No router is being used as a switch. We only have 1 router x.x.x.1 It's strange because the even log shows the conflicted IP and the MAC, but I don't see that MAC when I can the network.
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by:snurker
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Are you still getting the errors? There is a possibility that it erred and the system received a new IP and is fine. Is the IP conflict in your DHCP range?
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by:timgreen7077
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The ip conflict is in the DHCP range, but my problem is I scanned the mac address on my LAN and no mac matches the one in error event logs. I can't figure out where it came from. i'm not getting an error now so it must have resolved itself but that MAC is not on any machine, printer, scanner, pc or anything.
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snurker earned 500 total points
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There could be a number of reasons for something like that from a guest user coming in, Cell phones that may have a static account or any of the like having a static ARP address. The success of this was that it is no longer there and thus, you are not having further issues.

The reason I mentioned VMs was because i have seen it often be a VM and these even resolve themselves. Many VMs are built from another machine's image and thus, it would have many of the same settings including ip and name. Even Dynamic, there is a possibility that at first, both IPs were registered and then one of the conflicts released and renewed.

The other likely scenario is that you do have some device on your network that is not showing up with your MAC address scan that has a static IP in your scope range. This means that it is possible that this conflict will return.

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