Great news! My new book, Implementing Always On VPN, is now available for pre-order on Amazon.com. This new book, scheduled for release in late 2021, is a comprehensive implementation guide for Windows 10 Always On VPN. Drawing on many years of experience deploying Always On VPN for organizations worldwide, it covers all aspects of an Always On VPN deployment, including planning and design, prerequisite gathering, infrastructure preparation, and client deployment.
In addition, it contains detailed, prescriptive guidance for advanced configuration options such as application and traffic filtering and proxy server configuration. Cloud deployments using Azure VPN gateway and Virtual WAN are covered, and it includes guidance for configuring Azure MFA and Conditional Access.
Also, the book includes thorough guidance for provisioning certificates using Microsoft Endpoint Manager/Intune using both PKCS and SCEP. It outlines options for high availability for VPN and authentication infrastructure and provides details for ongoing system maintenance and operational support.
Finally, the book has an entire chapter dedicated to troubleshooting and resolving common (and not so common!) issues encountered with Windows 10 Always On VPN.
Using Microsoft Endpoint Manager (Intune), administrators can provision Always On VPN to devices that are Azure AD joined only. Users accessing on-premises resources from these devices can still use seamless single sign-on, making this deployment option popular for organizations moving to the cloud.
Short Names
After deploying Always On VPN to Windows 10 devices that are Azure AD joined only and configured to use client certificate authentication, administrators may find that users cannot access on-premises resources by their short name, such as \\app1. The connection fails and returns the following error message.
“Windows can’t find <servername/sharename>. Check the spelling and try again.”
FQDN
Interestingly, on-premises resources are accessible using their fully qualified domain name (FQDN), such as \\app1.corp.example.net.
Troubleshooting
Testing name resolution using the short name works as expected, and the resource is reachable at the network layer, as shown here.
Workaround
This issue is related to how Windows performs authentication when connected via VPN. To resolve this issue, edit the rasphone.pbk file and change the value of UseRasCredentials to 0. Rasphone.pbk can be found in the $env:AppData\Microsoft\Network\Connections\Pbk folder.
After updating this setting, restart the VPN connection for the change to take effect.
Proactive Remediations
While helpful for testing, editing rasphone.pbk manually obviously does not scale well. To address this, consider using Intune Proactive Remediations. Intune Proactive Remediations allows administrators to deploy detection and remediation PowerShell scripts to monitor specific settings and update them if or when they change. Proactive Remediations will ensure the setting is applied consistently across all managed endpoints.
GitHub Repository
I have created a new GitHub repository dedicated to PowerShell scripts for Endpoint Manager Proactive Remediations for Always On VPN. There you will find detection and remediation scripts for the UseRasCredentials settings change described in this article.
Integrating Microsoft Azure Conditional Access with Windows 10 Always On VPN has several important benefits. The most important is that it allows administrators to improve their security posture by enforcing access polices that can be dynamically applied. For example, requiring multifactor authentication (MFA) for privileged users (e.g., administrators) or sign-ins that appear to be risky, the type of device they are connecting with, the health of the endpoint, and much more.
Authentication Failure
When configuring Always On VPN to support Azure Conditional Access, administrators may expeirence a failed authentication during preliminary testing. Specifically, an event ID 20227 from the RasClient source may be encountered with the following error message.
“The user <username> dialed a connection named <connection name> which has failed. The error code returned on failure is 812.”
Looking at the event logs on the Network Policy Server (NPS) server reveals an event ID 6273 from the Microsoft Windows security auditing source with Reason Code 258 and the following Reason.
“The revocation function was unable to check revocation for the certificate.”
Root Cause
When Azure Conditional Access is configured for Always On VPN, a short-lived certificate (1 hour lifetime) is provisioned by Azure. This certificate does not include revocation information because, by design, a short-lived certificate does not need to be revoked. However, by default NPS always checks revocation when client authentication certificates are used for authentication. Since the certificate does not include this information, certificate revocation fails.
Resolution
The way to resolve this issue is to disable certificate revocation checking for Protected Extensible Authentication Protocol (PEAP) authentication requests. To do this, open an elevated PowerShell window on the NPS server and run the following command.
Windows Autopilot is a cloud-based technology that administrators can use to configure new devices wherever they may be, whether on-premises or in the field. Devices provisioned with Autopilot are Azure AD joined by default and managed using Microsoft Endpoint Manager. Optionally, an administrator can enable hybrid Azure AD join by also joining the device to an on-premises Active Directory domain using a domain join configuration profile in conjunction with the offline domain-join connector. Although enabling hybrid Azure AD join might sound appealing, there are specific deployment scenarios that present some rather unique and challenging problems when using this option.
Offline Hybrid Azure AD Join
For field-based devices, the device must have connectivity to a domain controller to support the initial login when the user has no local cached credentials. The Always On VPN device tunnel can be deployed in this scenario to provide connectivity and allow the user to log in to a new device the first time without being on-premises. The Always On VPN device tunnel is easily deployed using a Microsoft Endpoint Manager configuration profile. Certificates required to support the device tunnel can be deployed with Microsoft Endpoint Manager and one of the certificate connectors for Microsoft Endpoint Manager.
Windows 10 Professional
If a Windows 10 Professional device is configured using Autopilot, and hybrid Azure AD joined is enabled, the Always On VPN device tunnel can still be provisioned, but it won’t start automatically because it requires Enterprise Edition to be fully functional. This prevents the user from being able to logon the first time. The device must be upgraded to Enterprise Edition before the first user logon. There are multiple ways to accomplish this depending on the deployment scenario and activation requirements.
Multiple Activation Key
The easiest way to upgrade Windows 10 Professional to Enterprise Edition is to obtain a Multiple Activation Key (MAK) and deploy that to clients using a Microsoft Endpoint Manager configuration profile. Follow the steps below to create a configuration profile to perform this upgrade.
Open the Microsoft Endpoint Manager console and click on Devices > Configuration Profiles.
Click Create profile.
Select Windows 10 and later in the Platform drop-down list.
Select Templates in the Profile type drop-down list.
Select Edition upgrade and mode switch from the list of templates.
Click Create.
Use the following steps to configure the settings for the configuration profile.
Enter a descriptive name for the configuration profile in the Name field.
Enter a description for the profile in the Description field (optional).
Click Next.
Expand the Edition Upgrade section and select Windows 10 Enterprise from the Edition to upgrade to drop-down list.
Enter your multiple activation product key in the Product Key field.
Once complete, assign the configuration profile to the appropriate groups and click Create.
KMS Activation
If Key Management Service (KMS) activation is required, follow the steps listed previously for MAK. Enter the KMS client setup key for Windows 10 Enterprise which is NPPR9-FWDCX-D2C8J-H872K-2YT43. The device will complete KMS activation when it can connect to the on-premises KMS host.
Subscription Activation
Windows 10 Enterprise Edition licensing is included in some Microsoft 365 subscriptions. This poses a unique challenge for hybrid Azure AD join scenarios, however. Specifically, subscription activation is a “step-up” process that requires Windows 10 Professional to have been successfully activated previously. Also, this occurs after the user logs on, but the user cannot log on unless the device tunnel is active. Catch 22!
Workaround
A multi-step process is required to address the limitations imposed by subscription activation. To begin, the device must be upgraded to Enterprise Edition, so the device tunnel is available for the initial user logon. This is a temporary, one-time upgrade to Enterprise Edition solely for the purpose of getting the device tunnel to connect and allow the user to authenticate.
To begin, download this PowerShell script and follow the steps below to deploy it to Windows 10 devices using Microsoft Endpoint Manager.
Open the Microsoft Endpoint Manager console and click on Devices > Scripts.
Click Add and select Windows 10.
Enter a descriptive name for the configuration profile in the Name field.
Enter a description for the profile in the Description field (optional).
Click Next.
Enter the location of the PowerShell script in the Script location field.
Click Next, then assign the script to the appropriate device group(s) and click Add.
The PowerShell script will automatically install the KMS client setup key for Windows 10 Enterprise Edition, then restart the network interfaces to ensure the device tunnel starts. This will immediately upgrade the client device to Windows 10 Enterprise Edition and allow the user to authenticate.
Subscription activation with a step-up upgrade to Enterprise Edition still requires that Windows 10 Professional be activated first. To accomplish this, the embedded Windows 10 Professional key must be re-installed on the client. To do this, download this PowerShell script and follow the same steps listed previously to deploy a PowerShell script with Microsoft Endpoint Manager. However, this script should be assigned to users, not devices.
Once this script is run on the client it will be downgraded (temporarily) to Windows 10 Professional edition. After activation is successful, subscription activation will once again upgrade the client to Windows 10 Enterprise Edition.
Considerations
As you can see, the process of getting a Windows 10 Professional edition client onboarded in a hybrid Azure AD joined scenario is somewhat complex. My advice is to avoid this scenario whenever possible. Access to on-premises resources with the Always On VPN user tunnel with full single sign-on support is still available for users on Windows 10 devices that are Azure AD joined only. Unless there is a specific requirement to manage client devices using on-premises Active Directory and group policy, consider choosing native Azure AD join with Autopilot and manage devices using Microsoft Endpoint Manager exclusively.
Special Thanks
I would like to extend a special thank you to everyone in the Microsoft Endpoint Manager community who provided valuable input and feedback for me on this topic, especially John Marcum, Michael Niehaus, and Sandy Zeng. Follow the #MEMCM hashtag on Twitter to keep up on all things Microsoft Endpoint Manager.
