Configuring 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.”
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.”
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.”
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.
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
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
Tim
/ April 29, 2019It took me a long time get my head around MFA as the documentation is a little sparse. Rather than go down the route of using the MFA extension for NPS which is a on/off scenario (depending on MFA enrolment by the user), I ended up using Conditional Access with MFA for more flexibility, which allowed me to specify more granular requirements when asking for MFA authentication. However, doing this means I had to use the AAD certificate CA and issue sort-lived certificates from Azure AD and not the Internal CA issued certificates. Apart from that – and when when working, I have to say that the MFA functionality works very well.
Richard M. Hicks
/ April 29, 2019Using Azure conditional access is an excellent alternative to just using the NPS extension. The NPS extension for Azure MFA is certainly easy to configure and it works well, but you’re right, using AAD and conditional access does provide more granularity for sure. 🙂
Nate
/ July 9, 2019I spent a day troubleshooting this stupid thing. Opened a ticket with MS support and they sent links to the documentation which I had already read multiple times thinking I’d missed something. Turns out both enterprise apps were disabled and this article was what actually helped. Thanks, Richard!
While I’m writing, any thoughts on cert management for this? I’d like to use our internal CA so we can at least monitor the expiration date, but I’m not finding any guidance on configuring the template. Even then it still has to be uploaded to Azure. Just trying to come up with a way to make this manageable, otherwise it’ll be a reminder two years from now on a team calendar.
Thanks,
Nate
Richard M. Hicks
/ July 9, 2019Glad the post was helpful! 🙂 The Microsoft guidance here only states the syntax of the subject name. It doesn’t indicate what EKUs are required unfortunately. However, if you look at the configuration of the existing self-signed certificate that will give you an idea of what’s required.
Simon Brunner
/ July 10, 2019Hi Richard
we have an on Prem Installation of Always on VPN with User Tunnel in place. We decided to implement Azure MFA with NPS Extension. With one user the Setup is working great. With another user the Always on tunnel is working once and never again (until reboot). A third user was never able to establish a Connection (no mfa popup arrived). Any Idea?
Thanks
Simon
Richard M. Hicks
/ July 10, 2019Unusual for sure. If it is working for one user it should work for all users. I would suspect perhaps an issue with their Azure AD account perhaps? Are the users in question licensed for Azure MFA?
Mike M
/ August 1, 2019Hello, I am experiencing the same issue with our setup. Always on VPN was working perfectly until we implemented the MFA extension. Once MFA was turned on users would get the approval on their phone. Sometimes it would finish the connection but it fails enough to where we cant go to production with it. When it fails we generally don’t see the approval pop up on the phone to accept. Any ideas to where to look?
Richard M. Hicks
/ August 3, 2019Not sure about this one. I would suggest making sure your RADIUS timeout is set to at least 60 seconds, but if users aren’t receiving the notification from Azure, you’ll have to start investigating there.
Lee Humphreys
/ January 29, 2020Hi Richard,
My Always On VPN POC is now up and running, and after some initial hurdles seams relatively stable (deployed both Device Tunnel and User Tunnel with PEAP & User Certs).
The next step for the POC is to secure the User Tunnel with MFA. I’m aware that we can do this via Azure MFA with the NPS Extension, or using Conditional Access. My preference would be the CA route as it provides more flexibility, however I can’t find anything in the Microsoft documentation that explains how the enforcement is actually done. It appears from the documentation that this is only a Client side config – meaning that in theory you could create a VPN Profile that does not include the CA piece and it would happily connect – therefore bypassing CA?
The Azure MFA NPS Extension is more clear – every request to the NPS Server after it is enabled must pass MFA or it will fail to connect (which I like and is where we want to get to).
With the CA option, is there something that can be enforced Server side to ensure that all Clients must satisfy CA?
I hope that makes sense.
Thanks,
Lee
Richard M. Hicks
/ January 30, 2020I’m not certain that’s the case. If you have a CA policy configured for a user and this specific app (VPN) then I think they will be MFA’d according to your policy. I don’t believe that can be bypassed with a different client configuration. I could be wrong of course, but that’s my understanding today at least. 🙂
You’re right, using the Azure MFA NPS extension is a more positive way to enforce MFA, and it will require it for anyone who connects and for every login. However, this can be tiresome for end users so you have to consider the experience when you choose between the extension and Conditional Access.
Lee Humphreys
/ January 30, 2020I guess that’s something to test in my POC then – setup with CA, and then create a Profile without the entry for true, and see if it lets me connect without CA 🙂
Richard M. Hicks
/ January 30, 2020You certainly have to include configuration details in ProfileXML to support authentication, so you might find that you get prompted for MFA, but if your profile isn’t configured to use a different certificate for authenticating to internal resources you might be able to connect, but won’t have access to internal resources.
Lee Humphreys
/ January 30, 2020Not sure that formatted correctly 🙂 “true”
Lee Humphreys
/ January 30, 2020DeviceCompliance – Enabled – True as per: https://docs.microsoft.com/en-us/windows-server/remote/remote-access/vpn/vpn-create-oma-dm-based-vpnv2-profiles
Matt Klein
/ March 18, 2020We have Always On VPN working with Azure MFA – however because of EAP protocol it looks like it only works with MS Authenticator or Phone call (not PIN code responses –
https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension#configure-your-nps-extension
Am I missing something or does this not work with SMS code MFA from Azure MFA ??
Richard M. Hicks
/ March 18, 2020That’s correct. If you are using EAP authentication (recommended) then your only options for Azure MFA are push notification via the Authenticator app or phone call. No support for SMS in this scenario.
Rizmi
/ June 24, 2020Hi Richard, I used to go through all your step by step, concepts and troubleshooting on NPS extension deployment and integrating Azure MFA for Always ON VPN. I am struck in a place where I have specified PAP authentication method (assuming PAP will support phone call, one-way text message, mobile app notification, and mobile app verification code). But, in Windows 10 I do not find a prompt in UX to input Text and Verification Code. Please advise whether I am on right page and if so, help me on this regard.
Richard M. Hicks
/ June 29, 2020Always On VPN does not support PAP authentication. Only EAP and MS-CHAP v2 are supported.