Mysterious Disappearing MAC Address

One of my systems applied a Windows 10 updates on Friday, it runs attached to my TV, and so while not headless(ie. no attached monitor) it often runs for days without the UI visible. So there it was, has anyone ever clicked “Let’s Go”?

The system wasn’t connected the Internet? Puzzling, since it has a 1Gb wired connection into a switch, that goes straight to the 1Gb Fibre Optic cable modem, and everything else was working.

Choose Adapter settings > Disable > Enable > Wait > Identifying Network... > No Network Connection.

Next up was a CMD prompt and IPCONFIG /ALL

Strangely, it reported the IP V4 address as 169.x.x.x – no DNS etc. Then I spotted it, Physical Address: 00-00-00-00-00-00

I tried all the usual things:

Disable Adapter > Delete Driver > Shutdown/Reboot

and variations of that. Then went ahead and started searching on the web, that was as helpful as it always. They only thing I learned is, I was far from alone. Especially with Realtek PCIe GBE Family Controller users. I downloaded their device diagnostics, and everything ran clean, and right there in the diagnostics window was the supposedly zero-d out MAC/Physical address.

VPN Software?

I checked with the support team with NORDVPN that runs on that system, they assured me they do NOT change the MAC address, or use any form of MAC Spoofing in their software.

No Connectivity

The reason for the Internet connectivity issue, is that the cable modem I use, will not give out DNS data and assign an IP address to a device that is not on the list of devices I maintain.

Among the various reports of issues relating to this, I found this one. So there is every possibility that it was a #Windows #WIN10 update that screwed up the MAC address which is stored in the registry, who knows? Also, everyone of the posts I found recommended an app to store and update a new MAC Address. I’m not a big fan of either using REGEDIT and downloading and installing random apps to update the registry.

Setting a MAC Address in Windows 10

Turns out you don’t need to. If you go into the properties for the adapter, and scroll through them, you’ll come to the “Network Address”.

In the value field should be the same MAC address that is on the label that came with the PC. It also should match the MAC address you can find in the BIOS if you want to go rooting around in there. If you have the MAC address, for example, from PC Hardware case, you can simply add that back in at (3) above and select (4) OK. Just make sure you get the correct MAC address, don’t duplicate one already on your network, and don’t use the MAC address from your Wifi adapter, for your Ethernet adapter.

A Picture I found online. Don’t do this especially with a label that includes your Dell Service tag… trust me on that.

You can also look up your provider MAC address prefixes, here, and make a new one. Again, the MAC address does need to be unique. In my case I had the original, but decided while working through this issue to use a MAC Address starting with FCCF62 and is from a block assigned to “IBM Corp”. Since I don’t have any IBM devices on my network and am unlikely to have any.

My system has been fine since fixing this. The change survived through a couple of reboots, and I re-installed NORDVPN and it’s also working fine.

Why Post?

First obviously was to document what I’d done; Second was to share what had happened and how I resolved it; Third was in hope someone would post with a logical discussion of how this happened, and also, how I could have resolved it more simply and quickly.

I remain amazed that the Realtek diagnostics, a). loaded their own MAC address from Windows registry and b). didn’t at least recognize the MAC address wasn’t from a block they own?

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About & Contact

I'm Mark Cathcart, formally a Senior Distinguished Engineer, in Dells Software Group; before that Director of Systems Engineering in the Enterprise Solutions Group at Dell. Prior to that, I was IBM Distinguished Engineer and member of the IBM Academy of Technology. I am a Fellow of the British Computer Society ( I'm an information technology optimist.

I was a member of the Linux Foundation Core Infrastructure Initiative Steering committee. Read more about it here.

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