There appears to be a bug in the latest Windows 11 26H1 (no, that’s not a typo – 26H1) build affecting Protected Extensible Authentication Protocol (PEAP). In my testing, all VPN connection attempts (Always On VPN and manual/ad-hoc) failed when PEAP was used for authentication.
Windows 11 26H1
Recently, while reviewing downloads and product keys in Visual Studio, I noticed a new Windows 11 release listed: Windows 11 26H1 (business and consumer editions). I initially thought 26H1 would be ARM-only, but the download is available for x64 as well.
I’m not sure whether this is intended as a general release, because Microsoft describes it as an Insider Experimental Preview Build (28200.1873). I also don’t recall seeing Insider builds offered through Visual Studio downloads, so I’m not sure what to make of it. Either way, if you’re evaluating this build, the notes below document a VPN issue I was able to reproduce.
Troubleshooting
After preparing a Windows 11 26H1 test client, I found that the Always On VPN user tunnel would not connect. The same configuration worked on earlier Windows 11 versions. In the event log, I observed the following errors.
Error 619
When using SSTP, the event log records error code 619 (event ID 20227) from the RasClient event source, with the following error message.
The user [domain\user] dialed a connection named [connection name] which has failed. The error code returned on failure is 619.
Error 691
When using IKEv2, the event log records error code 691 (event ID 20227) from the RasClient event source, with the following error message.
The user [domain\user] dialed a connection named [connection name] which has failed. The error code returned on failure is 691.
Workaround
At the time of writing, the only workaround I’ve found to restore Always On VPN connectivity is to switch authentication from PEAP to EAP-TLS. This may not be a drop-in change for every environment, so evaluate the security and operational impact before rolling it out broadly. You’ll need to enable EAP-TLS on both the client and the NPS/RADIUS server.
Summary
I’m not convinced Windows 11 26H1 will be widely deployed soon, since it appears to be an experimental/Insider build rather than a general release. If you decide to evaluate it, plan to use the workaround above to maintain Always On VPN connectivity.
Feedback
Have you tested Always On VPN with Windows 11 26H1? If so, do you see the same behavior? Share your findings in the comments.
Additional Information
Windows 11 Insider Experimental (26H1) Preview Build 28200.1873
