Denying Access to Always On VPN Users or Computers

Denying Access to Always On VPN Users or ComputersOnce Windows 10 Always On VPN has been deployed in production, it may be necessary at some point for administrators to deny access to individual users or computers. Commonly this occurs when an employee is terminated or leaves the company, or if a device is lost, stolen, or otherwise compromised. Typically, this means that user accounts and computer accounts in Active Directory are disabled, and any issued certificates are revoked. However, additional steps may be required to disconnect current VPN sessions or prevent future remote connections.

Certificate Revocation

When certificates are used for authentication, for example when a device tunnel is deployed, or a user tunnel is configured to use Extensible Authentication Protocol (EAP) with user certificate authentication, immediately revoking issued user and device certificates and publishing a new Certificate Revocation List (CRL) is recommended. However, this will not instantly prevent VPN access because revocation information is cached on the VPN and NPS servers, as well as any online responders. The process of flushing certificate revocation caches is challenging and time consuming as well.

Blocking Users

To immediately prevent users from accessing the VPN, a security group must be created in Active Directory that contains users that will be denied access. In addition, a Network Policy must be created on the Network Policy Server (NPS) that denies access to users belong to this security group.

NPS Configuration

Once the security group has been created, open the NPS management console (nps.msc) and perform the following steps.

  1. Expand Policies.
  2. Right-click Network Policies and choose New.
  3. Enter a descriptive name for the policy in the Policy name field.
  4. Select Remote Access Server (VPN-Dial up) from the Type of network access server drop-down list.
  5. Click Next.
  6. Click Add.
    1. Select User Groups.
    2. Click Add.
    3. Click Add Groups.
    4. Select the security group create for denied users.
    5. Click Ok twice.
  7. Click Next.
  8. Select Access denied.
  9. Click Next four times and click Finish.

Denying Access to Always On VPN Users or Computers

Denying Access to Always On VPN Users or Computers

Once complete, move the deny access policy so that it is before the policy that allows VPN access.

Denying Access to Always On VPN Users or Computers

Device Tunnel Considerations

Since device tunnel connections don’t use the NPS for authentication, blocking devices from establishing Always On VPN connections requires a different technique. Once again, revoking the computer certificate and publishing a new CRL is recommended, but isn’t immediately effective. To address this challenge, it is recommended that the computer certificate issued to the client be retrieved from the issuing CA and placed in the local computer’s Untrusted Certificates store on each VPN server, as shown here.

Note: The certificate must be imported on each VPN server in the organization.

Terminating Connections

Once the guidance above is put in to place, any user or device that is denied access will be unable to connect to the VPN. However, if a user or device is currently connected when these changes are implemented, additional steps must be taken to proactively terminate their existing session. When using Windows Server Routing and Remote Access Service (RRAS) as the VPN server, uUser sessions can be proactively terminated using RRAS management console or PowerShell.

GUI

To terminate an established Always On VPN connection, open the RRAS management console (rrasmgmt.msc), highlight Remote Access Clients, then right-click the client connection and choose Disconnect. Repeat the process for any additional connections established by the user or device.

Denying Access to Always On VPN Users or Computers

PowerShell

Alternatively, Always On VPN connections can also be terminated programmatically using PowerShell. To identify currently connected users on a VPN server, open an elevated PowerShell command window and run the following command.

Get-RemoteAccessConnectionStatistics | Format-Table -AutoSize

Next, to disconnect a user tunnel, identify the User Principal Name (UPN) of the user to disconnect and include it in the following PowerShell command.

Disconnect-VpnUser -UserName “user@corp.example.net”

To disconnect a device tunnel, identify the Fully-Qualified Domain Name (FQDN) of the device to disconnect and include it in the following PowerShell command.

Disconnect-VpnUser -UserName “client1.corp.example.net”

Additional Information

Windows 10 Always On VPN Hands-On Training

Always On VPN and Network Policy Server (NPS) Load Balancing

Always On VPN and Network Policy Server (NPS) Load BalancingLoad balancing Windows Server Network Policy Servers (NPS) is straightforward in most deployment scenarios. Most VPN servers, including Windows Server Routing and Remote Access Service (RRAS) servers allow the administrator to configure multiple NPS servers for redundancy and scalability. In addition, most solutions support weighted distribution, allowing administrators to distribute requests evenly between multiple NPS servers (round robin load balancing) or to distribute them in order of priority (active/passive failover).

The Case for NPS Load Balancing

Placing NPS servers behind a dedicated network load balancing appliance is not typically required. However, there are some deployment scenarios where doing so can provide important advantages.

Deployment Flexibility

Having NPS servers fronted by a network load balancer allows the administrator to configure a single, virtual IP address and hostname for the NPS service. This provides deployment flexibility by allowing administrators to add or remove NPS servers without having to reconfigure VPN servers, network firewalls, or VPN clients. This can be beneficial when deploying Windows updates, migrating NPS servers to different subnets, adding more NPS servers to increase capacity, or performing rolling upgrades of NPS servers.

Traffic Shaping

Dedicated network load balancers allow for more granular control and of NPS traffic. For example, NPS routing decisions can be based on real server availability, ensuring that authentication requests are never sent to an NPS server that is offline or unavailable for any reason. In addition, NPS traffic can be distributed based on server load, ensuring the most efficient use of NPS resources. Finally, most load balancers also support fixed or weighted distribution, enabling active/passive failover scenarios if required.

Traffic Visibility

Using a network load balancer for NPS also provides better visibility for NPS authentication traffic. Most load balancers feature robust graphical displays of network utilization for the virtual server/service as well as backend servers. This information can be used to ensure enough capacity is provided and to monitor and plan for additional resources when network traffic increases.

Configuration

Before placing NPS servers behind a network load balancer, the NPS server certificate must be specially prepared to support this unique deployment scenario. Specifically, the NPS server certificate must be configured with the Subject name of the cluster, and the Subject Alternative Name field must include both the cluster name and the individual server’s hostname.

Always On VPN and Network Policy Server (NPS) Load Balancing

Always On VPN and Network Policy Server (NPS) Load Balancing

Create Certificate Template

Perform the following steps to create a certificate template in AD CS to support NPS load balancing.

  1. Open the Certificate Templates management console (certtmpl.msc) on the certification authority (CA) server or a management workstation with remote administration tool installed.
  2. Right-click the RAS and IAS Servers default certificate template and choose Duplicate.
  3. Select the Compatibility tab.
    1. Select Windows Server 2008 or a later version from the Certification Authority drop-down list.
    2. Select Windows Vista/Server 2008 or a later version from the Certificate recipient drop-down list.
  4. Select the General tab.
    1. Enter a descriptive name in the Template display name field.
    2. Choose an appropriate Validity period and Renewal period.
    3. Do NOT select the option to Publish certificate in Active Directory.
  5. Select the Cryptography tab.
    1. Chose Key Storage Provider from the Provider Category drop-down list.
    2. Enter 2048 in the Minimum key size field.
    3. Select SHA256 from the Request hash drop-down list.
  6. Select the Subject Name tab.
    1. Select the option to Supply in the request.
  7. Select the Security tab.
    1. Highlight RAS and IAS Servers and click Remove.
    2. Click Add.
    3. Enter the security group name containing all NPS servers.
    4. Check the Read and Enroll boxes in the Allow column in the Permissions for [group name] field.
  8. Click Ok.

Perform the steps below to publish the new certificate template in AD CS.

  1. Open the Certification Authority management console (certsrv.msc) on the certification authority (CA) server or a management workstation with remote administration tool installed.
  2. Expand Certification Authority (hostname).
  3. Right-click Certificate Templates and choose New and Certificate Template to Issue.
  4. Select the certificate template created previously.
  5. Click Ok.

Request Certificate on NPS Server

Perform the following steps to request a certificate for the NPS server.

  1. Open the Certificates management console (certlm.msc) on the NPS server.
  2. Expand the Personal folder.
  3. Right-click Certificates and choose All Tasks and Request New Certificate.
  4. Click Next.
  5. Click Next.
  6. Select the NPS server certificate template and click More information is required to enroll for this certificate link.
  7. Select the Subject tab.
    1.  Select Common name from the Type drop-down list in the Subject name section.
    2. Enter the cluster fully-qualified hostname (FQDN) in the Value field.
    3. Click Add.
    4. Select DNS from the Type drop-down list in the Alternative name section.
    5. Enter the cluster FQDN in the Value field.
    6. Click Add.
    7. Enter the NPS server’s FQDN in the Value field.
    8. Click Add.
      Always On VPN and Network Policy Server (NPS) Load Balancing
  8. Select the General tab.
    1. Enter a descriptive name in the Friendly name field.
  9. Click Ok.
  10. Click Enroll.

Load Balancer Configuration

Configure the load balancer to load balance UDP ports 1812 (authentication) and 1813 (accounting). Optionally, to ensure that authentication and accounting requests go to the same NPS server, enable source IP persistence according to the vendor’s guidance. For the KEMP LoadMaster load balancer, the feature is called “port following”. On the F5 BIG-IP it is called a “persistence profile”, and on the Citrix NetScaler it is called a “persistency group”.

Additional Information

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Always On VPN Hands-On Training Classes in U.S. and Europe

Always On VPN and Windows Server 2019 NPS Bug

Note: This post updated March 19,2019 to reflect new workaround configuration guidance.

When deploying a Windows Server 2019 Network Policy Server (NPS) to support a Windows 10 Always On VPN implementation, administrators may encounter the following error when attempting to establish a VPN connection on a remote Windows 10 client.

Can’t connect to [connection name].

The connection was prevented because of a policy configured on your RAS/VPN server. Specifically, the authentication method used by the server to verify your username and password may not match the authentication method configured in your connection profile. Please contact the Administrator of the RAS server and notify them of this error.

Always On VPN and Windows Server 2019 Network Policy Server Bug
In addition, an event ID 20227 from the RasClient will be recorded in the application event log 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.

Always On VPN and Windows Server 2019 Network Policy Server Bug

Common Causes

Always On VPN error code 812 indicates an authentication policy mismatch between the client and the server. This often occurs when, for example, the server is configured to use Protected Extensible Authentication Protocol (PEAP), but the client is configured to use Microsoft CHAP Version 2 (MS-CHAP v2).

Troubleshooting

Carefully review the authentication policy on both the client and server to ensure they match. Next, enable firewall logging on the NPS server to log both allowed and dropped packets. Attempt another VPN connection and observe the firewall logs. In this example the firewall is dropping packets inbound on UDP port 1812.

Always On VPN and Windows Server 2019 Network Policy Server Bug

Interestingly, the default Windows firewall rule allowing inbound UDP port 1812 is enabled and set to allow for all profiles.

Always On VPN and Windows Server 2019 Network Policy Server Bug

Windows Server 2019 Bug

It appears that Microsoft’s recently released Windows Server 2019 has a bug that prevents NPS from working correctly out of the box. Specifically, it looks like the default Windows firewall rules to allow inbound UDP port 1812 (RADIUS authentication) and inbound UDP port 1813 (RADIUS accounting) do not work.

Resolution

To resolve this issue, open an elevated command window and enter the following command.

sc sidtype IAS unrestricted

Once complete, restart the server and the default Windows Firewall rules for NPS traffic will work correctly.

Additional Information

Windows 10 Always On VPN NPS Load Balancing Strategies

NetMotion Mobility Device Tunnel Configuration

NetMotion Mobility Device Tunnel ConfigurationIn its default configuration, NetMotion Mobility connections are established at the user level. In most cases this level of access is sufficient, but there are some common uses cases that require VPN connectivity before the user logs on. Examples include provisioning a new device to a user who has never logged on before, or to allow support engineers to connect to a remote device without requiring a user to log in first.

Infrastructure Requirements

To support NetMotion Mobility’s “unattended mode” (device tunnel) it will be necessary to deploy a Windows Server 2016 (or 2012R2) Network Policy Server (NPS). In addition, an internal private certification authority (CA) will be required to issue certificates to the NPS server and all NetMotion Mobility client computers.

Client Certificate Requirements

A certificate with the Client Authentication Enhanced Key Usage (EKU) must be provisioned to the local computer certificate store on all NetMotion Mobility clients that require a device tunnel (figure 1). The subject name on the certificate must match the fully qualified domain name of the client computer (figure 2). It is recommended that certificate auto enrollment be used to streamline the provisioning process.

NetMotion Mobility Device Tunnel Configuration

Figure 1. Computer certificate with Client Authentication EKU.

NetMotion Mobility Device Tunnel Configuration

Figure 2. Computer certificate with subject name matching the client computer’s hostname.

NPS Server Certificate Requirements

A certificate with the Server Authentication EKU must be provisioned to the local computer certificate store on the NPS server (figure 3). The subject name on the certificate must match the fully qualified domain name of the NPS server (figure 4).

NetMotion Mobility Device Tunnel Configuration

Figure 3. Computer certificate with Server Authentication EKU.

NetMotion Mobility Device Tunnel Configuration

Figure 4. Computer certificate with subject name matching the NPS server’s hostname.

NPS Server Configuration

Next install the NPS server role by running the following PowerShell command.

Install-WindowsFeature NPAS -IncludeMamagementTools

Once complete, open the NPS server management console and perform the following steps.

Note: Below is a highly simplified NPS configuration designed for a single use case. It is provided for demonstration purposes only. The NPS server may be used by more than one network access server (NAS) so the example policies included below may not work in every deployment.

  1. Expand RADIUS Clients and Servers.
  2. Right-click RADIUS clients and choose New.
  3. Select the option to Enable this RADIUS client.
  4. Enter a friendly name.
  5. Enter the IP address or hostname of the NetMotion gateway server.
  6. Click Verify to validate the hostname or IP address.
  7. Select Manual to enter a shared secret, or select Generate to create one automatically.
  8. Copy the shared secret as it will be required when configure the NetMotion Mobility gateway server later.
  9. Click OK.
    NetMotion Mobility Device Tunnel Configuration
  10. Expand Policies.
  11. Right-click Network Policies and choose New.
  12. Enter a descriptive name for the new policy.
  13. Select Type of network access server and choose Unspecified.
  14. Click Next.
    NetMotion Mobility Device Tunnel Configuration
  15. Click Add.
  16. Select Client IPv4 Address.
  17. Click Add.
  18. Enter the internal IPv4 address of the NetMotion Mobility gateway server.
  19. Click OK.
  20. Click Next.
    NetMotion Mobility Device Tunnel Configuration
  21. Select Access granted.
  22. Click Next.
    NetMotion Mobility Device Tunnel Configuration
  23. Click Add.
  24. Choose Microsoft: Protected EAP (PEAP).
  25. Click OK.
  26. Select Microsoft: Protected EAP (PEAP).
  27. Click Edit.
  28. Choose the appropriate certificate in the Certificate issued to drop down list.
  29. Select Secure password (EAP-MSCHAP v2).
  30. Click Remove.
  31. Click Add.
  32. Choose Smart Card or other certificate.
  33. Click OK.
  34. Select Smart Card or other certificate.
  35. Click Edit.
  36. Choose the appropriate certificate in the Certificate issued to drop down list.
  37. Click OK.
    NetMotion Mobility Device Tunnel Configuration
  38. Uncheck all options beneath Less secure authentication methods.
  39. Click Next three times.
  40. Click Finish.
    NetMotion Mobility Device Tunnel Configuration

Mobility Server Configuration

Open the NetMotion Mobility management console and perform the following steps.

  1. In the drop-down menu click Configure.
  2. Click Authentication Settings.
  3. Click New.
  4. Enter a descriptive name for the new authentication profile.
  5. Click OK.
  6. Expand Authentication.
  7. Select Mode.
  8. Select Unattended Mode Authentication Setting Override.
  9. From the Authentication mode drop-down box choose Unattended.
  10. Click Apply.
    NetMotion Mobility Device Tunnel Configuration
  11. Expand RADIUS: Device Authentication.
  12. Select Servers.
  13. Select [Profile Name] Authentication Setting Override.
  14. Click Add.
  15. Enter the IP address of the NPS server.
  16. Enter the port (default is 1812).
  17. Enter the shared secret.
  18. Click OK.
    NetMotion Mobility Device Tunnel Configuration
  19. In the drop-down menu click Configure.
  20. Click Client Settings.
  21. Expand Device Settings.
  22. Select the device group to enable unattended mode for.
  23. Expand Authentication.
  24. Select Settings Profile.
  25. Select [Device Group Name] Group Settings Override.
  26. In the Profile drop-down menu choose the authentication profile created previously.
  27. Click Apply.
    NetMotion Mobility Device Tunnel Configuration

Validation Testing

If everything is configured correctly, the NetMotion Mobility client will now indicate that the user and the device have been authenticated.

NetMotion Mobility Device Tunnel Configuration

Summary

Enabling unattended mode with NetMotion Mobility provides feature parity with DirectAccess machine tunnel and Windows 10 Always On VPN device tunnel. It ensures that domain connectivity is available before the user logs on. This allows users to log on remotely without cached credentials. It also allows administrators to continue working seamlessly on a remote computer after a reboot without having a user present to log on.

Additional Resources

NetMotion Mobility as an Alternative to DirectAccess

 

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