Always On VPN Authentication Failure with Azure Conditional Access

Always On VPN Clients Prompted for Authentication when Accessing Internal Resources

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.

New-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\13\’ -Name IgnoreNoRevocationCheck -PropertyType DWORD -Value 1 -Force

Once complete, restart the NPS server for the changes to take effect.

Additional Information

Windows 10 Always On VPN Network Policy Server (NPS) Load Balancing

Windows 10 Always On VPN Network Policy Server (NPS) Server 2019 Bug

Always On VPN and Azure MFA ESTS Token Error

Always On VPN and Azure MFA ESTS Token ErrorConfiguring Multifactor Authentication (MFA) is an excellent way to ensure the highest level of assurance for Always On VPN users. Azure MFA is widely deployed and commonly integrated with Windows Server Network Policy Server (NPS) using the NPS Extension for Azure MFA. Azure MFA has a unique advantage over many other MFA providers in that it supports MFA when using Protected Extensible Authentication Protocol (PEAP). This makes Azure MFA the solution of choice for integrating with Windows 10 Always On VPN deployments using client certificate authentication, a recommended security configuration best practice.

NPS Configuration

Installing and configuring the NPS extension for Azure MFA is straightforward. Configuration guidance from Microsoft can be found here.

Connection Issues

After installing the NPS extension for Azure MFA, administrators may find that Always On VPN connections fail and the user is never challenged for authentication. The connection eventually times out and returns the following error message.

“A connection to the remote computer could not be established, so the port used for this connection was closed.”

Always On VPN and Azure MFA ESTS Token Error

In addition, the Application event log on the Windows 10 client contains an Event ID 20221 from the RasClient source that includes the following error message.

“The user [username] dialed a connection named [connection] which has failed. The error code returned on failure is 0.”

Always On VPN and Azure MFA ESTS Token Error

NPS Event Log

Reviewing the event logs on the NPS server reveals more information. The Security event log contains an Event ID 6274 from the Microsoft Windows security auditing source that includes the following error message.

“Network Policy Server discarded the request for a user. Contact the Network Policy Administrator for more information.”

Always On VPN and Azure MFA ESTS Token Error

ESTS Token Error

Digging deeper in the operational event log on the NPS server, the AuthZAdminCh log (Applications and Services Logs > Microsoft > AzureMfa > AuthZ) contains an Event ID 3 from the AuthZ source indicating an ESTS_TOKEN_ERROR message.

Always On VPN and Azure MFA ESTS Token Error

Troubleshooting ESTS Token Error

Follow the steps below to troubleshoot the ESTS_TOKEN_ERROR.

Prerequisites

Ensure that all prerequisites are met. Validate the user is being synced to Azure Active Directory and that it is properly licensed for Azure MFA.

Certificates

As part of the NPS extension configuration, a certificate is created on the NPS server that is uploaded to Azure Active Directory. To validate the certificate was created and uploaded correctly, follow the troubleshooting guidance found here.

Enterprise Applications

The Azure Multi-Factor Auth Client and the Azure Multi-Factor Auth Connector enterprise applications must be enabled to support the NPS extension for Azure MFA. To confirm they are enabled, open an elevated PowerShell command window on the server where the Azure AD Connector is installed and run the following PowerShell commands.

Import-Module MSOnline
Connect-MsolService

Get-MsolServicePrincipal -AppPrincipalId “981f26a1-7f43-403b-a875-f8b09b8cd720” | Select-Object DisplayName, AccountEnabled

Get-MsolServicePrincipal -AppPrincipalId “1f5530b3-261a-47a9-b357-ded261e17918” | Select-Object DisplayName, AccountEnabled

Always On VPN and Azure MFA ESTS Token Error

If either or both enterprise applications are not enabled, enable them using the following PowerShell commands.

Set-MsolServicePrincipal -AppPrincipalId “981f26a1-7f43-403b-a875-f8b09b8cd720” -AccountEnabled $True

Set-MsolServicePrincipal -AppPrincipalId “1f5530b3-261a-47a9-b357-ded261e17918” -AccountEnabled $True

Once complete, restart the IAS service on the NPS server using the following PowerShell command.

Restart-Service IAS -PassThru

Additional Information

Windows 10 Always On VPN Network Policy Server (NPS) Load Balancing Strategies

Deploy Windows 10 Always On VPN with Microsoft Intune

Windows 10 Always On VPN Hands-On Training Classes Now Available

Always On VPN and the Future of Microsoft DirectAccess

Windows 10 Always On VPN hands-on training classes now forming. Details here.

Since the introduction of Windows Server 2012 in September of 2012, no new features or functionality have been added to DirectAccess. In Windows Server 2016, the only real change aside from bug fixes for DirectAccess is the removal of Network Access Protection (NAP) integration support.

Always On VPN and the Future of Microsoft DirectAccessFigure 1. Remote Access Setup wizard with NAP integration option in Windows Server 2012/R2.

Always On VPN and the Future of Microsoft DirectAccess

Figure 2. Remote Access Setup wizard without NAP integration option in Windows Server 2016.

DirectAccess Roadmap

It’s clear to see that Microsoft is no longer investing in DirectAccess, and in fact their field sales teams have been communicating this to customers for quite some time now. Microsoft has been actively encouraging organizations who are considering a DirectAccess solution to instead implement client-based VPN with Windows 10.

Always On VPN

New features introduced in the Windows 10 Anniversary Update allow IT administrators to configure automatic VPN connection profiles. This Always On VPN connection provides a DirectAccess-like experience using traditional remote access VPN protocols such as IKEv2, SSTP, and L2TP/IPsec. It comes with some additional benefits as well.

  • Conditional access and device compliance with system health checks
  • Windows Hello for Business and Azure multifactor authentication
  • Windows Information Protection (WIP) integration
  • Traffic filters to restrict VPN network access
  • Application-trigger VPN connections

DirectAccess Deprecated?

There has been rampant speculation that Microsoft plans to deprecate and retire DirectAccess. While that may in fact be true, Microsoft has yet to make a formal end-of-life announcement. There’s no reason DirectAccess and VPN couldn’t co-exist, so it’s not a certainty Microsoft will do this. However, there’s also no need to have multiple remote access solutions, and it is abundantly clear that the future for Microsoft remote access is Always On VPN and not DirectAccess.

Always On VPN and the Future of Microsoft DirectAccess

Source: https://social.technet.microsoft.com/wiki/contents/articles/38546.new-features-for-vpn-in-windows-10-and-windows-server-2016.aspx#Advanced_VPN_Connectivity

Always On VPN Advantages and Disadvantages

Windows 10 Always On VPN has some important advantages over DirectAccess. It has some crucial limitations as well.

Advantages

  • Always On VPN supports non-Enterprise Windows 10 client SKUs (Windows 10 Home and Professional)
  • Always On VPN includes support for granular network access control
  • Always On VPN can use both IPv4 and IPv6
  • Always On VPN is infrastructure independent. In addition to supporting Windows RRAS, any third-party network device can be used such as Cisco, Checkpoint, Juniper, Palo Alto, SonicWALL, Fortinet, and many more

Disadvantages

  • Always On VPN works only with Windows 10. It is not supported for Windows 7
  • Always On VPN cannot be managed natively using Active Directory and group policy. It must be configured and managed using Microsoft Intune. Alternatively, Microsoft System Center Configuration Manager (SCCM) or PowerShell can be used.

DirectAccess or Always On VPN?

Should you deploy DirectAccess today or implement Always On VPN with Windows 10 instead? That depends on a number of factors. It’s important to understand that DirectAccess will be fully supported through the lifecycle of Windows Server 2019. If DirectAccess meets your needs today, you can deploy it with confidence that it will still have a long support life. If you have reservations about the future viability of DirectAccess, and if you meet all of the requirements to support Always On VPN with Windows 10, then perhaps that’s a better choice. If you’d like to discuss your remote access options in more detail, fill out the form below and I’ll get in touch with you.

Additional Resources

5 Things DirectAccess Administrators Should Know About Always On VPN

3 Important Advantages of Always On VPN over DirectAccess

NetMotion Mobility as an Alternative to DirectAccess

Windows 10 Always On VPN Hands-On Training Classes

 

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