Using Windows Server Network Policy Server (NPS) servers is a common choice for authenticating Microsoft Windows 10 Always On VPN user tunnel connections. The NPS server is joined to the domain and configured with a Network Policy that defines the authentication scheme used by clients for authentication when establishing an Always On VPN connection. Protected Extensible Authentication Protocol (PEAP) using client authentication certificates recommended for most Always On VPN deployment scenarios.
Experiencing error 853 on Windows 11? Click here for more information.
Can’t Connect
Users establishing an Always On VPN user tunnel connection using PEAP and client authentication certificates may encounter a scenario in which a VPN connection attempt fails with the following error message.
“The remote access connection completed, but authentication failed because the certificate that authenticates the client to the server is not valid. Ensure that the certificate used for authentication is valid.”
Error 853
In addition, the Application event log records an event ID 20227 from the RasClient source that includes the following error message.
“The user <username> dialed a connection named <connection name> which has failed. The error code is 853.”
Missing NTAuth Certificate
Error code 853 is commonly caused by a missing issuing Certification Authority (CA) certificate in the NTAuth store on the NPS server. The NPS server must have the issuing CA certificate included in this store to perform authentication using client certificates. You can see the contents of the NTAuth certificate store by opening an elevated command window on the NPS server and running the following command.
certutil.exe -enterprise -viewstore NTAuth
Install Certificate
To install the issuing CA server’s certificate into the NTAuth store, copy the CA certificate to the NPS server, open an elevated command window, then run the following command.
certutil.exe -enterprise -addstore NTAuth <issuing CA certificate>
Once complete, view the store again, and you’ll see the issuing CA certificate listed in the NTAuth certificate store.
Additional Information
Always On VPN Error 853 on Windows 11
Troubleshooting Always On VPN Error Code 858
Troubleshooting Always On VPN Error Code 864
Always On VPN and Windows Server 2019 NPS Bug
When configuring a Windows Routing and Remote Access Service (RRAS) server to support Internet Key Exchange version 2 (IKEv2) VPN connections, it is essential for the administrator to define the root certification authority for which to accept IPsec security associations (SAs). Without defining this setting, the VPN server will accept a device certificate issued by any root certification authority defined in the Trusted Root Certification Authorities store. Details about configuring IKEv2 security and defining the root certification authority can be found 
