NCSI problems after the update KB5129195

Question

Hello to the microsoft community,

Since I have installed the update KB5129195 on Windows 11 Pro 25H2 with also Hyper-V installed, the NCSI (NlaSvc) service seems to have stopped working. Also the affected network adapter is a Hyper vSwitch.

The last NCSI log entry I have is from 2026-09-25 where I have installed this update and after that no log entry anymore. But I have restarted the machine multiple times, no change.

Another log entry in the NlaSvc logs appears after every reboot with Event-ID 4205 with failure code 0x43.

Also I executed sfc /scannow and it also reapaired a file named C:\WINDOWS\SysWOW64\\srmlib.dll. After that and a reboot, still no change. So I also executed DISM /Online /Cleanup-Image /RestoreHealth.

The status in Get-NetConnectionProfile is "NoTraffic" and also in the Settings app it shows up that it is not physically connected, which is incorrect. Ignore the IPv6 status, because IPv6 is disabled on the adapter.

But the status I got from the WinRT-API is: "LocalAccess".

I have execute that via PowerShell to check: [Windows.Networking.Connectivity.NetworkInformation]::GetInternetConnectionProfile().GetNetworkConnectivityLevel() and got: LocalAccess

The output from Get-NetConnectionProfile is the following:

Name                     : Netzwerk 3
InterfaceAlias           : vEthernet (Mellanox-Switch-10G)
InterfaceIndex           : 4
NetworkCategory          : Public
DomainAuthenticationKind : None
IPv4Connectivity         : NoTraffic
IPv6Connectivity         : NoTraffic

The status in the Settings app:

(Unfortunately I only have a screenshot in German language.)

I also tried to restart the NLA Service more than one time, no change.

Since I´m not a Windows expert but must troubleshoot the thing I can´t really offer a path to reproduce, but I try:

1. Install the update KB5129195.
2. Restart the machine
3. Get-NetConnectionProfile status stucks in "NoTraffic"

I hope there is someone of the Windows pro´s out there that can help me to resolve that issue or that maybe a Microsoft employee look at it, so it can be fixed in the next update ;)

Regards,

MM

Answer 1

@Allan Solomon Mejia Thanks for your answer.

I see now I forgot to say multiple things 😅, sorry for that.

1. The machine should not show an "Internet access" icon in the taskbar because that machine don´t have unrestricted internet connection.
2. I disabled passive probing with GPO.
3. All HTTP/HTTPS connections goes over a proxy server that controls to where connection is allowed. (The www.msftconnecttest.com is redirected to an internal web server that delivers a connecttest.txt with a wrong content to (usually) force that "Local access only" (or sth. like that) shows up in the Settings app and the taskbar to indicate that machine has no unconstrained internet access. But now it shows up as "no connection"😬)
4. I think that I have uninstalled the update KB5129195, but because I don´t have good windows knowledge I dont know if it was successful removal. I look for that again.

I have already enabled the analytic & debug logs and tested again now what you have written (and what I also read in the Microsoft KB).
I don´t see any HTTP packets on the vEthernet-Adapter in Wireshark after I deactivated it and reactivate it then.

But the NCSI service debug log says with a warning that the active internet probe has finished with result code 0. (I don´t know if 0 means successful like in linux or it means failed or sth. like that)

Answer 2

Hi @MElectronicsIT-8004

Your results show that the vEthernet adapter is present, but Windows is not assigning it a usable NCSI connectivity state. NCSI uses both active probes and passive traffic observations; therefore, NoTraffic from Get-NetConnectionProfile and LocalAccess from the WinRT API are related indicators, but they are not necessarily identical measurements.

At present, Microsoft’s KB5129195 release notes do not list an NCSI, NlaSvc, or Hyper‑V virtual switch problem as a known issue. Therefore, I cannot confirm that this is a recognized KB5129195 regression.

Please perform these checks:

1. From the affected host, open: http://www.msftconnecttest.com/connecttest.txt

The response must be the expected Microsoft Connect Test text. If it fails or is modified, check whether a proxy, firewall, DNS filter, VPN, or security product is blocking or altering the request. This is the standard NCSI browser test.

2. In Event Viewer, open: Applications and Services Logs > Microsoft > Windows > NCSI

Select View > Show Analytic and Debug Logs, enable the Analytic log, and then disable/re-enable the vEthernet adapter or restart the computer to reproduce the problem. Microsoft recommends correlating these events with a packet capture when diagnosing NCSI failures.

Confirm that active probing has not been disabled and that the NCSI configuration under the following location has not been changed by policy or security software: HKLM\SYSTEM\CurrentControlSet\Services\NlaSvc\Parameters\Internet

Do not change these values without first comparing them with Microsoft’s documented defaults.

Because the last NCSI event coincides with the update installation, temporarily removing KB5129195, if your change management and security policies permit it, and checking whether NCSI logging resumes would establish a stronger correlation. That alone would not prove the update is the cause.

I cannot find verified official documentation defining NlaSvc Event ID 4205 with failure code 0x43 for this specific Hyper‑V/NCSI scenario.

If the issue reproduces immediately after reinstalling KB5129195, collect the NCSI Operational/Analytic logs and a network trace, then submit them through Microsoft Support or Feedback Hub with the affected build number and the vSwitch configuration. Microsoft will need that evidence to confirm whether this is an update regression.

References:

KB5129195 release information

Microsoft NCSI troubleshooting guidance

How to collect data to diagnose NCSI issues

NCSI overview

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