Duplicate computer GUIDs in Active Directory

15 pts.
Active Directory
When we use RIS to image computers, we sometime get errors indicating there are duplicate GUIDs in the directory. I'm totally lost. I thought GUIDs were based off the MAC address of the NIC. This doesn't happen all the time, we only see this error when we PXE boot the computers. We never see the error when booting computers with RIS boot disks. Any help/ideas are greatly appreciated. Toby

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In some cases, namely PXE Boot, the GUID is based on the MAC. The MAC is supposed to be unique – but this actully isn’t always so. This, however, should be rare. If you move the NIC around or have a failure of the installation process and start over, you can have a problem with the GUID already being registered in AD. This issues is alluded to in the following article:


In the article (at the bottom) it discusses how the duplication can occur if you move NICs. However, if there is a failure in the initial installation and the installation is started over, you can have the problem as well. This can be a timing issues as well – in other words an installation fails and the deletion of the GUID from AD doesn’t occur immediately and the installation is re-tried. You get the warning, but if you wait a moment you can retry without a problem. Occassionally, I have heard that AD edits for the object in question are necessary (ADSIEdit works). I have never personnally experienced having to do an edit for this purpose, but understand it to be possible.


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  • TJMann
    Thanks for the information you provided Paul! The MS article was helpful. I think I have another issue though because now, when we RIS certain machines RIS reports that there are multiple GUIDs and list anywhere from 3 to 6 machines as duplicates. It appears to only happen on older machines 466 and 600 MHZ machines. It's really weird. Thanks in advance! Toby
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