No network access for one VM (6 running fine). Hyper-V

Mikael Hallen 6

I have a Hyper-v environment that have been fully functional for years.

As of yesterday my file server no longer can access our network. No network access.
I can reach it through our hyperv servers and have tried restarted it and resetting ever since.
I have 6 more VMs that connects without problem.

The VM is server 2019. Hyper-V servers are 2012.

I have one more 2019 server and the only difference in network setup is the driver of the NIC.
Microsoft Hyper-V Network Adapter - 10.0.17763.2145 (driver date 2006-06-21) not working
Microsoft Hyper-V Network Adapter - 10.0.17763.1577 (driver date 2006-06-21) which is working.

I find it hard to believe that this driver is causing the problem but it is the only difference I have noticed.

Tried both static and dynamic IP for the server, no luck.

I have deleted and added the network adapter several times.

I have deleted one of the virtual switch and added a new one. tried the new switch with other VM and it works.

but my file server still has no network access.

Any thoughts?

Brad Smith 1 Reputation point

2021-09-26T16:46:24.997+00:00

I've run into the exact problem. Installed from the Aug_2021 ISO, which comes with 10.0.17763.1879 of the Microsoft Hyper-V Network Adapter. Networking worked fine at that point. Eventually I decided to run Windows Update, which didn't offer much. But on rebook, the driver had been updated to 10.0.17763.2145, and I lost all network access. Nothing I did could get it working again. Installing all the updates I could didn't help, so I suspect one of the uninstallable updated did the deed.

I ended up reinstalling from scratch, and resisting the temptation to run Windows Update for now.

This is definitely something introduced in a recent update. Showing as available now (and I'm not taking them):
KB5005568 and KB4535680, plus one Defender AV update and an update to the Malicious Software Removal. I suspect the latter two aren't related, it's one of those other updates. I'm suspecting the first one: 2021-09 Cumulative Update for Windows Server 2019 (1809) for x64-based Systems (KB5005568).
Jay B 6 Reputation points

2021-09-30T18:45:29.547+00:00

I'm also seeing the same behavior after installing KB5005568 on Server 2019 VMs running on a Server 2012 Hyper-V host. For me it's been very consistent across three Server 2019 VMs so far- install KB5005568 and network access stops; remove KB5005568 and it comes back. It's a Dell R910 with Broadcom/QLogic NICs, and the symptoms are the same as what's described in https://learn.microsoft.com/en-US/troubleshoot/windows-server/networking/vm-lose-network-connectivity-broadcom, although that article obviously pre-dates the Sept.2021 CU. I updated the physical NIC drivers to the QLogic 17.2 release and disabled virtual machine queuing on all of them anyway, but that hasn't changed the behavior. I hadn't checked the virtual NIC driver versions before reading this post but on a post-KB5005568 VM (non-functional network) it's 10.0.17763.2145, and on one with KB5005568 rolled back it's 10.0.17763.1 (and the network is accessible).

So the Sept. 2021 CU (KB5005568) on the VMs definitely seems to be the problem, or what triggers it anyway.
Brad Smith 1 Reputation point

2021-10-01T18:15:05.21+00:00

Since this is mostly a test VM, I decided to upgrade it to Windows Server 2022. Which upgraded the driver. Which broke networking. So it's much more than just 2019 September CU, but also the latest version of Windows 2022.

One thing I noticed with this driver update is I have a whack of "WAN Miniport" drivers that weren't there before.
Jay B 6 Reputation points

2021-10-01T22:12:46.987+00:00

I haven't installed 2022 anywhere yet but I can at least say that pre-2019 versions don't seem to have the same issue. Two Server 2016 VMs and one Server 2012 R2 on the same host still have functional networking after their respective September 2021 CUs.
JLugo-ITCS 6 Reputation points

2021-10-05T13:15:27.84+00:00

Same problem. We tried removing the KBs without luck. I guess we are waiting for a fix. I'm currently using the legacy adapter while this is resolved.
David Ortiz 1 Reputation point

2021-11-22T22:19:18.617+00:00

We encountered the same issue. Purchased new copy of Server 2019 Standard w/CALs. Setup new VM with previously used Virtual NIC Settings.
All was well until installing Windows Updates. After Windows Updates the server could not connect to any networks.
We tried different Virtual NICs and TCP reset commands. But nothing worked, until removing the windows updates. We removed the following, then we are able to connect to a network:
KB4514366, KB4512577, KB5007206.

Looks like we will also be waiting for Microsoft to correct this issue, before anymore Windows Updates.

12 answers

Pavel Dvorak 11 Reputation points

2021-10-26T13:42:37.057+00:00

I had the same problem. It helped to turn off the virtual machine, add a Legacy network adapter, and turn the virtual machine back on. Then all I had to do was to reconfigure TCP/IP on the network card (leave the legacy card unconfigured or disable it) and then the network started working again. The virtual system was 2016 and the Hyper-v server was 2012 R2.
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Dave Patrick 426K Reputation points MVP

2021-09-02T17:03:37.97+00:00

An unedited ipconfig /all of working / non-working may help.
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Mikael Hallen 6 Reputation points

2021-09-02T17:27:26.15+00:00

of course. first is working second is not.
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Dave Patrick 426K Reputation points MVP

2021-09-02T17:32:22.813+00:00

Is the top a domain controller?
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Mikael Hallen 6 Reputation points

2021-09-02T17:34:05.897+00:00

both are domain controllers
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