The Internet Key Exchange version 2 (IKEv2) VPN protocol is the protocol of choice for Windows 10 Always On VPN deployments where the highest levels of security and assurance are required. However, as I’ve written about in the past, often the default IKEv2 security settings are less than desirable. Before using IKEv2 VPN in a production environment the administrator will need to update these security settings accordingly.
Connection Failure
When configuring Windows Server Routing and Remote Access Service (RRAS) or a third-party VPN appliance to support IKEv2 using custom security policies, the administrator may encounter a scenario in which a connection cannot be established due to a policy mismatch error. When the connection attempt fails, an error will be recorded in the Windows Application event log from the RasClient source with Event ID 20227. The error message states the following:
“The user [username] dialed a connection named [connection name] which has failed. The error code returned on failure is 13868.”
Error Code 13868
Error code 13868 translates to ERROR_IPSEC_IKE_POLICY_MATCH. Essentially this error indicates that the IKEv2 security policy on the client did not match the configuration on the server.
Server Configuration
To view the current IKEv2 IPsec policy configuration, open an elevated PowerShell command window and run the following command.
Get-VpnServerIPsecConfiguration
Client Configuration
To ensure interoperability, the VPN client must be configured to use the same IKEv2 security policy as defined on the sever. To view a VPN client’s currently configured IKEv2 security policy, open an elevated PowerShell command window and run the following command.
Get-VpnConnection -Name [connection name] | Select-Object -ExpandProperty IPsecCustomPolicy
Note: If this PowerShell command returns no output, the VPN connection is not using a custom IKEv2 IPsec security policy.
Updating Settings
Guidance for configuring IKEv2 security policies on Windows Server RRAS and Windows 10 can be found here.
Summary
IKEv2 policy mismatch errors can be resolved easily by ensuring both the VPN server and client are configured to use the same IPsec security policies. Use the PowerShell commands in the above referenced above to validate settings and make changes when necessary.
Additional Information
Windows 10 Always On VPN IKEv2 Security Configuration
Windows 10 Always On VPN IKEv2 Features and Limitations
Show-VpnConnectionIPsecConfiguration PowerShell script on Github
Recently I wrote about 
When configuring Always On VPN, administrators have the option to enable DNS registration for VPN clients. When this option is set, VPN clients will register the IP address assigned to their VPN interface in the internal DNS. This allows client devices to be managed using their hostname from the internal network whenever they are connected remotely.
After deploying or upgrading to Windows 10 1903, administrators may find that Windows 10 Always On VPN connections fail to establish successfully. Always On VPN connections continue to work for Windows 10 1809 and earlier clients, however.
The Windows Server Routing and Remote Access Service (RRAS) includes support for the Secure Sockets Tunneling Protocol (SSTP), which is a Microsoft proprietary VPN protocol that uses SSL/TLS for security and privacy of VPN connections. The advantage of using SSTP for Always On VPN is that it is firewall friendly and ensures consistent remote connectivity even behind highly restrictive firewalls.
Important! Updated July 15, 2019 to support all versions of Windows Server including Windows Server 2012 and 2012 R2. Also added functionality to renew self-signed certificates individually.
When an Always On VPN connection is provisioned to a Windows 10 client, there’s nothing to prevent a user from disconnecting or even deleting the connection. Some administrators have expressed concern about this, fearful that users may disable the VPN to improve performance or circumvent access controls when force tunneling is enabled. Also, administrators may wish to prevent users from accidentally or purposefully making changes to the configuration, or even deleting the connection entirely.
