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Always On VPN – Install and Configure the NPS Server

Harmik Batth Tech's Blog

Always On VPN – Install and Configure the NPS Server

You can use this section to install the Network Policy Server (NPS) and perform configuration for Always On VPN.

NPS server processing
of connection requests that are sent by the VPN server includes performing
authorization – to verify that the user has permission to connect; performing
authentication – to verify the user’s identity; and performing accounting – to
log the aspects of the connection request that you chose when you configured
RADIUS accounting in NPS.

The steps in this
section allow you to complete the following items.

  1. On the computer or VM that is planned as the NPS server, and that is installed on the corporate network, you can install NPS.

Tip

If you already have one
or more NPS servers on your network, you do not need to perform NPS Server
installation – instead, you can use this topic to update the configuration of
an existing NPS server.

  • On the corporate NPS server, you can configure NPS to perform as a RADIUS server that processes the connection requests that are received from the VPN server.

You can use this
section to install Network Policy Server (NPS) by using either Windows
PowerShell or the Server Manager Add Roles and Features Wizard.

NPS is a role service
of the Network Policy and Access Services server role.

Note

By default, NPS listens for RADIUS traffic on
ports 1812, 1813, 1645, and 1646 on all installed network adapters. If Windows
Firewall with Advanced Security is enabled when you install NPS, firewall
exceptions for these ports are automatically created during the installation
process for both Internet Protocol version 6 (IPv6) and IPv4 traffic. If your
network access servers are configured to send RADIUS traffic over ports other
than these defaults, remove the exceptions created in Windows Firewall with
Advanced Security during NPS installation, and create exceptions for the ports
that you do use for RADIUS traffic.

Administrative
Credentials

Membership in Administrators, or equivalent, is the minimum required to
perform these procedures.

To perform this
procedure by using Windows PowerShell, run Windows PowerShell as Administrator,
type the following command, and then press ENTER.

Install-WindowsFeature NPAS
-IncludeManagementTools

You can use the
following procedure to install NPS using Server Manager.

  1. In Server Manager, click Manage, and then click Add Roles and Features. The Add Roles and Features Wizard opens.
  2. In Before You Begin, click Next.

Note

The Before You Begin page of the Add Roles and Features
Wizard is not displayed if you have previously selected Skip this page by default when the Add Roles and Features Wizard
was run.

  • In Select Installation Type, ensure that Role-Based or feature-based installation is selected, and then click Next.
  • In Select destination server, ensure that Select a server from the server pool is selected. In Server Pool, ensure that the local computer is selected. Click Next.
  • In Select Server Roles, in Roles, select Network Policy and Access Services. A dialog box opens asking if it should add
    features that are required for Network Policy and Access Services. Click Add Features, and then click Next
  • In Select features, click Next, and in Network Policy and Access Services, review the information that is provided, and
    then click Next.

  • In Select role services, click Network
    Policy Server
    . In Add features that are required for Network
    Policy Server
    , click Add Features. Click Next.

  • In Confirm installation selections, click Restart the destination server automatically if required. When you are prompted to confirm this
    selection, click Yes, and then click Install. The Installation progress page displays status during the
    installation process. When the process completes, the message
    “Installation succeeded on ComputerName” is displayed,
    where ComputerName is the name of the computer upon which you
    installed Network Policy Server. Click Close.

NPS handles all
authentication, authorization, and accounting duties for connection requests
that it receives from the VPN server.

To configure NPS, you
must perform the following tasks.

  • Register the NPS
    Server in Active Directory
  • Configure RADIUS
    Accounting for your NPS Server
  • Add the VPN Server as
    a RADIUS Client in NPS
  • Configure Network
    Policy in NPS
  • Autoenroll the NPS
    Server certificate

The following sections
provide instructions on completing these tasks.

After you install NPS,
you must register the server in Active Directory so that it has permission to
access user account information while processing connection requests.

To register
the NPS Server in Active Directory

  1. In Server Manager,
    click Tools, and then click Network Policy Server. The NPS console opens.
  2. In the NPS console,
    right-click NPS (Local), and then click Register server in Active Directory. The Network Policy Server dialog box opens.

  3. In the Network Policy Server dialog box, click OK twice.

For alternate methods
of registering NPS, see Register an NPS Server in an Active Directory
Domain
.

There are three types
of logging for Network Policy Server (NPS):

  • Event
    logging
    . Used primarily for
    auditing and troubleshooting connection attempts. You can configure NPS event
    logging by obtaining the NPS server properties in the NPS console.
  • Logging
    user authentication and accounting requests to a local file
    . Used primarily for connection analysis and
    billing purposes. Also useful as a security investigation tool because it
    provides you with a method of tracking the activity of a malicious user after
    an attack. You can configure local file logging using the Accounting
    Configuration wizard.
  • Logging
    user authentication and accounting requests to a Microsoft SQL Server
    XML-compliant database
    .
    Used to allow multiple servers running NPS to have one data source. Also
    provides the advantages of using a relational database. You can configure SQL
    Server logging by using the Accounting Configuration wizard.

To learn how to
configure NPS Accounting, see Configure Network Policy Server Accounting.

Implemented

You can use this
section to configure the VPN server as a RADIUS Client in NPS.

Note

When you add a new network access server (VPN
server, wireless access point, authenticating switch, or dial-up server) to
your network, you must add the server as a RADIUS client in NPS so that NPS is
aware of and can communicate with the network access server.

To add the VPN
Server as a RADIUS client in NPS

You can use this
procedure to configure a new RADIUS client in NPS.

Important

In the previous deployment step using the
topic Configure the Remote Access Server for Always
On VPN
, you installed and
configured your VPN server. During VPN server configuration, you added a RADIUS
shared secret on the VPN server. Now you need to use the same shared secret
text string to configure the VPN server as a RADIUS client in NPS. You must use
the same text string that you used on the VPN server, or communication between
the NPS server and VPN server will fail.

  1. On the NPS server, in Server Manager,
    click Tools, and then click Network Policy Server. The NPS console opens.

  2. In the NPS console, double-click RADIUS Clients and Servers. Right-click RADIUS Clients, and then click New. The New
    RADIUS Client
     dialog box
    opens.

  3. In New RADIUS Client, verify that the Enable this RADIUS client check box is selected.
  4. In New RADIUS Client, in Friendly
    name
    , type a display name
    for the VPN server. In Address
    (IP or DNS)
    , type the NAS IP
    address or fully qualified domain name (FQDN). If you enter the FQDN,
    click Verify if you want to verify that the name is
    correct and maps to a valid IP address.
  5. In New RADIUS Client, in Shared
    secret
    , do the following:

    1. Ensure that Manual is selected, and then in Shared secret, type the strong text string that you also
      entered on the VPN server. Retype the shared secret in Confirm shared secret.
  6. OK. The VPN Server appears in the list of RADIUS clients that are
    configured on the NPS server.

You can use this procedure to configure NPS as a RADIUS server on your network.

On the NPS server, you must define a policy that allows only users in a specific group to access the Corporate network through the VPN Server – and then only when using a valid user certificate in a PEAP authentication request.

To configure the NPS
Network Policy on the NPS server

  1. On the NPS server, in Server Manager,
    click Tools, and then click Network Policy Server.
  2. In Standard Configuration, ensure that RADIUS server for Dial-Up or VPN Connections is selected, and then click Configure VPN or Dial-Up.
    The Configure VPN or
    Dial-Up
     wizard opens.

  3. In the Configure VPN or Dial-Up wizard, in Select Dial-up or Virtual Private Network Connections Type page, click Virtual Private Network (VPN) Connections, and then click Next.
  4. In Specify Dial-Up or VPN Server, in RADIUS clients, click the name of the VPN Server that you
    added in the previous step. For example, if your VPN server NetBIOS name is
    RAS1, click RAS1. Click Next.

  5. In Configure Authentication Methods, complete the following steps:

a. Deselect the Microsoft Encrypted Authentication version 2 (MS-CHAPv2) check box.

b. Select the Extensible Authentication Protocol check box.

c. Click Type (based on method of access and network configuration), and then click Microsoft: Protected EAP (PEAP). d. Click Configure. The Edit
Protected EAP Properties
 dialog
box opens.

e. In Edit
Protected EAP Properties
,
click Remove to remove the Secured Password (EAP-MSCHAP v2) EAP type.

f. Click Add. The Add EAP dialog box opens. In Add EAP, click Smart
Card or other certificate
,
and then click OK.

g. Click OK to close Edit Protected EAP Properties.

  • Click Next.
  • In Specify User Groups, complete the following steps:

a. Click Add. The Select Users, Computers, Service Accounts, or
Groups
 dialog box
opens.

b. In Select
Users, Computers, Service Accounts, or Groups
, type VPN
Users
, and then click OK.

c. Click Next.

  • In Specify IP Filters, click Next.
  • In Specify Encryption Settings, do not make any changes. These settings apply only to
    Microsoft Point-to-Point Encryption (MPPE) connections, which this scenario
    doesn’t support. Click Next.

  • In Specify a Realm Name, click Next.
  • Click Finish to close the
    wizard.

You can use this procedure
to manually refresh Group Policy on the local NPS server. When Group Policy is
refreshed, if certificate autoenrollment is configured and functioning
correctly, the local computer is autoenrolled a certificate by the
certification authority (CA).

Note

Group Policy is automatically refreshed when
you restart the domain member computer, or when a user logs on to a domain
member computer. In addition, Group Policy is periodically refreshed. By
default, this periodic refresh is performed every 90 minutes with a randomized
offset of up to 30 minutes.

Membership in Administrators, or equivalent, is the minimum required to
complete this procedure.

  1. On the computer where NPS is installed, open
    Windows PowerShell.
  2. At the Windows PowerShell prompt, type gpupdate, and then press ENTER.

The Network Policy Server (NPS) extension for Azure MFA adds cloud-based
MFA capabilities to your authentication infrastructure using your existing
servers. With the NPS extension, you can add phone call, text message, or phone
app verification to your existing authentication flow without having to
install, configure, and maintain new servers.

This extension was created for organizations that want to protect VPN
connections without deploying the Azure MFA Server. The NPS extension acts as
an adapter between RADIUS and cloud-based Azure MFA to provide a second factor
of authentication for federated or synced users.

When using the NPS extension for Azure MFA, the authentication flow
includes the following components:

  1. NAS/VPN Server receives
    requests from VPN clients and converts them into RADIUS requests to NPS
    servers.
  2. NPS Server connects to
    Active Directory to perform the primary authentication for the RADIUS requests
    and, upon success, passes the request to any installed extensions.
  3. NPS Extension triggers a
    request to Azure MFA for the secondary authentication. Once the extension
    receives the response, and if the MFA challenge succeeds, it completes the
    authentication request by providing the NPS server with security tokens that
    include an MFA claim, issued by Azure STS.
  4. Azure MFA communicates
    with Azure Active Directory to retrieve the user’s details and performs the
    secondary authentication using a verification method configured to the user.

  1. Download
    the NPS Extension
     from the Microsoft Download Center.
  2. Copy the binary to the
    Network Policy Server you want to configure.
  3. Run setup.exe and follow
    the installation instructions. If you encounter errors, double-check that the
    two libraries from the prerequisite section were successfully installed.

If you have users that
aren’t enrolled for MFA, you can determine what happens when they try to
authenticate. Use the registry setting REQUIRE_USER_MATCH in
the registry path HKLM\Software\Microsoft\AzureMFA to
control the feature behavior. This setting has a single configuration option:

Key Value Default
REQUIRE_USER_MATCH TRUE/FALSE Not set (equivalent to TRUE)

The purpose of this
setting is to determine what to do when a user is not enrolled for MFA. When
the key does not exist, is not set, or is set to TRUE, and the user is not enrolled,
then the extension fails the MFA challenge. When the key is set to FALSE and
the user is not enrolled, authentication proceeds without performing MFA. If a
user is enrolled in MFA, they must authenticate with MFA even if
REQUIRE_USER_MATCH is set to FALSE.

The installer creates a
PowerShell script in this location: C:\Program Files\Microsoft\AzureMfa\Config (where C:\ is your
installation drive). This PowerShell script performs the following actions each
time it is run:

  • Create a self-signed certificate.
  • Associate the public key of the certificate to the service
    principal on Azure AD.
  • Store the cert in the local machine cert store.
  • Grant access to the certificate’s private key to Network User.
  • Restart the NPS.

Unless you want to use
your own certificates (instead of the self-signed certificates that the
PowerShell script generates), run the PowerShell Script to complete the
installation. If you install the extension on multiple servers, each one should
have its own certificate.

  1. Run Windows PowerShell as
    an administrator.

  2. Change directories.

cd "C:\Program Files\Microsoft\AzureMfa\Config"

  • Run the PowerShell script created by the installer.

.\AzureMfaNpsExtnConfigSetup.ps1

  • Sign in to Azure AD as an administrator.
  • PowerShell prompts for your tenant ID. Use the Directory ID GUID that you copied from the Azure portal in the prerequisites section.
    • Enter Directory id
  • PowerShell shows a success message when the script is finished.

Repeat these steps on any
additional NPS servers that you want to set up for load balancing.

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