When implementing Windows 10 Always On VPN, administrators may encounter errors 691 or 812 when establishing a VPN connection. There are several different configuration issues that will result in these errors. For example they may occur when TLS 1.0 has been disabled on the RRAS server when installed on servers prior to Windows Server 2016. It can also happen if a user’s Active Directory account is configured to deny dial-in access and the NPS server is not configured to ignore user account dial-in properties. Another scenario that can result in 691/812 errors is when the Active Directory security groups are configured as conditions on the Network Policy Server (NPS) Network Policy. See below for more details.
SSTP and Error 691
When attempting to establish an Always On VPN connection using the Secure Socket Tunneling Protocol (SSTP), administrators may encounter the following error message.
“The remote connection was denied because the user name and password combination you provided is not recognized, or the selected authentication protocol is not permitted on the remote access server.”
In addition, an error 691 with event ID 20227 from the RasClient source can be found in the Application event log on the client.
“The user <domain\user> dialed a connection named which has failed. The error code returned on failure is 691.”
IKEv2 and Error 812
When attempting to establish an Always On VPN connection using Internet Key Exchange version 2 (IKEv2), administrators may encounter the following error message.
“The connection as prevented because of a policy configured on your RAS/VPN server. Specifically, the authentication method used by the server to verify your username and password may not match the authentication method configured in your connection profile. Please contact the Administrator of the RAS server and notify them of this error.”
In addition, an error 812 with event ID 20227 from the RasClient source can be found in the Application event log on the client.
NPS Event Log
On the NPS server the administrator will find an entry in the application event log with event ID 6273 from the Microsoft Windows security auditing source and the Network Policy Server task category indicating the network policy server denied access to the user. Looking closely at this event log message shows Reason Code 48 and the following reason.
“The connection request did not match any configured network policy.”
Group Membership
As stated earlier, another scenario in which administrators will encounter errors 691 and/or 812 is when the Network Policy on the NPS server is configured incorrectly. Specifically, and administrator may wish to grant access to more than one group but intend for access to be granted to users who are a member of any of them. Conversely, they may wish to require access in all specified groups to gain access to the VPN. Configuring each of these conditions is subtly different, however.
Open the NPS management console on the NPS server and follow the steps below to configure user group conditions correctly for the following scenarios.
Any Group
1. Right-click the Always On VPN network policy and choose Properties.
2. Click on the Conditions tab.
3. Click the Add button.
4. Click User Groups.
5. Click Add.
6. Click Add Groups.
7. Enter the name of the group you want to grant access to.
8. Click Ok.
9. Repeat the steps 6-8 above to specify additional groups.
All Groups
1. Right-click the Always On VPN network policy and choose Properties.
2. Click on the Conditions tab.
3. Click the Add button.
4. Click User Groups.
5. Click Add.
6. Click Add Groups.
7. Enter the name of the group you want to grant access to.
8. Click Ok.
9. Repeat steps 3-8 above to specify additional groups (you must go back to the Add button on step 3!).
Microsoft 
While performing Always On VPN evaluation testing with the latest release of Windows 10 (2004), a bug was discovered that may result in failed VPN connections, but only under certain conditions. Specifically, the failure occurs when both the device tunnel and user tunnel are configured on the same client, and the user tunnel is configured to use IKEv2 exclusively.
During the planning phase of a Windows 10 Always On VPN implementation the administrator must decide between two tunneling options for VPN client traffic – split tunneling or force tunneling. When split tunneling is configured, only traffic for the on-premises network is routed over the VPN tunnel. Everything else is sent directly to the Internet. With force tunneling, all client traffic, including Internet traffic, is routed over the VPN tunnel. There’s been much discussion recently on this topic, and this article serves to outline the advantages and disadvantages for both tunneling methods.
Over the last few weeks, I’ve worked with numerous organizations and individuals troubleshooting connectivity and performance issues associated with Windows 10 Always On VPN, and specifically connections using the Internet Key Exchange version 2 (IKEv2) VPN protocol. An issue that appears with some regularity is when Windows 10 clients fail to connect with error 809. In this scenario, the server will accept connections without issue for a period of time and then suddenly stop accepting requests. When this happens, existing connections continue to work without issue in most cases. Frequently this occurs with Windows Server Routing and Remote Access Service (RRAS) servers configured in a clustered array behind an External Load Balancer (ELB).
With the COVID-19 global pandemic forcing nearly everyone to work from home these days, organizations that implemented force tunneling for their VPN clients are likely encountering unexpected problems. When force tunneling is enabled, all client traffic, including Internet traffic, is routed over the VPN tunnel. This often overloads the VPN infrastructure and causes serious slowdowns, which degrades the user experience and negatively impacts productivity. This is especially challenging because so many productivity applications like Microsoft Office 365 are optimized for Internet accessibility. It is one of the main reasons that force tunneling is not generally recommended.
Recently I wrote about 
Unlike DirectAccess, Windows 10 Always On VPN settings are deployed to the individual user, not the device. As such, there is no support for logging on without cached credentials using the default configuration. To address this limitation, and to provide feature parity with DirectAccess, Microsoft later introduced the device tunnel option in Windows 10 1709.
