Windows 7 VM in Windows 10 Pro Hyper-V: after years, network no longer works

Question

I created a Windows 7 VM in Windows 10 Pro perhaps 5 years ago.

It worked fine for many years.

I rarely use this VM (maybe once every two or three months, sometimes longer) and very few changes have been made to this VM, but now suddenly the virtual NIC inside the VM is not working.

In other words, I get no IP address, and no connection to the real LAN or the Internet. Specifically, the NIC in Windows 7 now reports that it is on an "Unidentified Network" and seems to not be getting assigned an IP by DHCP.

I have no clue why this would happen, as no changes have been made to the VM settings, and the real NIC on the Windows 10 Pro hypervisor machine is working fine. Additionally, nothing has changed on the DHCP end (except for automatic updates to the Windows Server 2012 R2 machine running as the DHCP server) and DHCP is working perfectly for every other machine except this VM.

I'm assuming that one of the numerous automatic Windows updates that have been applied between five years ago and now "broke" something related to the VM configuration, but I have no idea where to even start looking for the problem.

I would guesstimate that the last time I used this VM without any problems was back in June-ish of 2022.

Can someone point me in a likely direction?

Answer 1

It is hard to pinpoint what may gone wrong. Also you should back up your VMs as often the fastest way to recover from an issue is to get the backup and use it.

Make sure your Guest Machines are backed up.

(1) First try remaking the Hyper-V Network Switch you used. If you used the Default Switch, you can remove that. Restart the host machine. Make a new Hyper-V Default Switch. Restart the host again. Go to the Guest machine settings and re-add the Default Switch.

Start the Guest and test.

(2) In the Guest machine, go to Network Properties

Click on Change Network Settings. Look at the Adapter Properties. Make sure Client for Microsoft Networks is enabled. Check other settings. Most (not all) should be enabled.

Restart the Guest and check.

(3) Consider reinstalling Hyper-V. Be very sure Guest VMs are backed up. Shut down any guests. Remove Hyper-V in Programs and Feature, Windows Features. Restart, re-add Hyper-V and restore your backups.

Double check Steps 1 and 2 because Step 3 WILL remove your guest machines (in my experience) and you MUST then restore them from backups.

Work carefully.

Finally, if has not proven practical to fix, and you do not use the Windows 7 machine much, you may find you can give up on it.

Windows 7 no longer updates, and downloads are not available from Microsoft.

Answer 2

My problem ended up being the result of a flaky/unstable Windows DHCP server failover configuration.

See here for more details:

Windows 10 Pro computer can no longer connect to or recognize domain network

It never crossed my mind that this could be a DHCP issue, because I couldn't fathom the host computer being able to get DHCP while the VM on the same physical network adapter could not.

Of course, this was a bad assumption on my part, since the virtual NIC on the VM would present itself to the network and to the DHCP server as a completely separate and independent, real and physical NIC because that's the whole point of a VM.