The Internet Key Exchange version 2 (IKEv2) VPN protocol is the protocol of choice for Microsoft 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.
NPS Policy
Another common cause of IKEv2 policy mismatch errors is a misconfigured Network Policy Server (NPS) network policy. Specifically, administrators may disable Basic and Strong encryption for MPPE in an attempt to improve security.
The NPS policy for Always On VPN must include Strong encryption at a minimum. Basic and No encryption can be safely disabled.
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
Microsoft Always On VPN Error 13801
Microsoft Windows Always On VPN Error 13806
Microsoft Windows Always On VPN Certificate Requirements for IKEv2
Microsoft Windows Always On VPN IPsec Root Certificate Configuration Issue
Microsoft Windows Always On VPN IKEv2 Policy Mismatch Error
Microsoft Windows Always On VPN IKEv2 Security Configuration
Microsoft Windows Always On VPN IKEv2 Fragmentation
Microsoft Windows Always On VPN IKEv2 Load Balancing and NAT
Microsoft Windows Always On VPN IKEv2 Features and Limitations
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