BUILD HIGH AVAILABLE REMOTE DESKTOP GATEWAY INTEGRATED WITH AZURE MFA

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    Build High Available Remote Desktop Gateway integrated with Azure MFA

    Implemented parts

    The following parts have been implemented:

    • On-Premises Infrastructure
    1. Microsoft Windows Server 2016 Standard Edition (3 Servers)
    2. A Highly Available Load Balanced RD Gateway Server Farm (RDG).
    3. Network Policy Server (Centralized NPS).
    • Enterprise Mobility + Security E3
    1. Microsoft Azure Multi-Factor Authentication

    Solution Requirements

    Prerequisites

    • Remote Desktop Gateway (RD Gateway) infrastructure
    • Azure MFA License
    • Windows Server software
    • Network Policy and Access Services (NPS) role
    • Azure Active Directory synched with on-premises Active Directory
    • Azure Active Directory GUID ID

    Network requirements

    The following table shows the required ports between RD Gateway, NPS Server, Internal network and WAN, and these ports must be opened for outbound and inbound

    Source Destination Protocol/Port
    Internet Gateway WAN NIC TCP: 443, 80

    UDP: 3391 (You have to enable UDP on the RD Gateway)Gateway LAN NICInternal networkTCP / UDP: 3389

    TCP: 5504

    TCP: 5985Gateway LAN NICDomain ControllersTCP / UDP: 88

    TCP: 135

    UDP: 123

    UDP 137

    TCP: 139

    TCP / UDP: 389

    TCP: 3268

    TCP / UDP: 53

    TCP / UDP: 445

    TCP: 5985

    TCP Dynamic Ports (NTDS RPC service)RD GatewayNPS ServerUDP: 1812

    UDP: 1813RD GatewayPerimeter network, should be opened for allowing HTTPS traffic from the client sitting on the Internet to the RD Gateway server in the perimeter network.TCP/ 443, 80

    Certificate requirements

    Public Certificate will be required that should contain the following SAN Names.

    Item

    SAN Names

    Domain Certificate

    RDS.3TALLAH.COM

    System requirements

    The following table shows the required subscription and license that should be provided by the time of the deployment:

    Product Name

    QTY

    Microsoft 365 subscription (E3 plan) or equivalent (MFA License)

    All users

    Microsoft Windows Server 2016 Standard Edition

    3

    The following table summarizes Microsoft products that will be deployed

    Product Name

    QTY

    Microsoft Windows Server 2016 Standard Edition

    3

    Network Policy and Access Services (NPS) role

    2

    Remote Desktop Gateway (RD Gateway) infrastructure

    2

    Authentication Flow

    1. F5 or any load balancer receives an Access request from a remote desktop user.
    2. F5 or any load balancer route the request to one of the RD Gateway serves.
    3. The Remote Desktop Gateway server receives an authentication request to connect to a resource, such as a Remote Desktop session. Acting as a RADIUS client, the Remote Desktop Gateway server converts the request to a RADIUS Access-Request message and sends the message to the RADIUS (NPS) server where the NPS extension is installed.
    4. The username and password combination are verified in Active Directory and the user is authenticated.
    5. If all the conditions as specified in the NPS Connection Request and the Network Policies are met (for example, time of day or group membership restrictions), the NPS extension triggers a request for secondary authentication with Azure MFA.
      1. Azure MFA communicates with Azure AD, retrieves the user’s details, and performs the secondary authentication using supported methods.
      2. Upon success of the MFA challenge, Azure MFA communicates the result to the NPS extension.
      3. The NPS server, where the extension is installed, sends a RADIUS Access-Accept message for the RD CAP policy to the Remote Desktop Gateway server.
    6. The user is granted access to the requested network resource through the RD Gateway.

    Deploy High-Available RD Gateway Server Farm

    Remote Desktop Gateway Server enables users to connect to remote computers on a corporate network from any external computer. The RD Gateway uses the Remote Desktop Protocol & the HTTPS Protocol to create a secure encrypted connection.

    RD Gateway server uses port 443 (HTTPS), which provides a secure connection using a Secure Sockets Layer (SSL) tunnel.

    Accounts

    All the following accounts have been used.

    Account or group name Source Description
    Guest001 Local AD Account for RD Gateway Access
    Office365 – EndUsers Local AD M365 Users License group
    Guest001@3tallah.Com Local AD Account to connect with Azure AD

    Environment

    Server details.

    Server Name IP Address Role
    RDG01P 192.168.1.16 Remote Desktop Gateway server role

    Network Policy Server (NPS) roleRDG02P192.168.1.17Remote Desktop Gateway server role

    Network Policy Server (NPS) role

    Install RD Gateway servers farm

    Install RD Gateway server role on both RD Servers farm

    Deploy NPS Role for NPS Extension server

    The Network Policy Server (NPS) extension for Azure Multi-Factor-Authentication (Azure MFA) provides a simple way to add cloud-based MFA capabilities to your authentication infrastructure using your existing NPS servers. With the NPS extension, you’ll be able to add phone call, SMS, or phone app MFA to your existing authentication flow without having to significantly increase your existing authentication infrastructure.

    Accounts

    All the following accounts have been used.

    Account or group name Source Description
    Guest001 Local AD Account for RD Gateway Access
    Office365 – EndUsers Local AD M365 Users License group
    Guest001@3tallah.Com Local AD Account to connect with Azure AD

    Environment

    Server details.

    Server Name IP Address Role
    NPSEx01 192.168.1.18 Network Policy Server (NPS) role

    NPS Extension for Azure MFA


    The next steps will install the NPS role in your new server:

    NPS Extension for Azure installation

    As a part of the configuration of the NPS extension, you need to supply admin credentials and the Azure AD ID for your Azure AD tenant. The following steps show you how to get the tenant ID:

    Get Azure AD ID

    Install the NPS extension

    1. Copy the setup executable file to the NPS server.
    2. On the NPS server, double-click the executable. If prompted, click Run.
    3. In the NPS Extension for Azure MFA dialog box, review the software license terms, check I agree to the license terms and conditions, and click Install.
    4. On the NPS Extension for Azure MFA dialog box, click Close.

    Configure certificates for use with the NPS extension

    In this step, you need to configure certificates for the NPS extension to ensure secure communications. The NPS components include a Windows PowerShell script that configures a self-signed certificate for use with NPS.

    This script performs the following actions:

    • Creates a self-signed certificate
    • Associates public key of certificate to service principal on Azure AD
    • Stores the cert in the local machine store
    • Grants access to the certificate’s private key to the network user
    • Restarts Network Policy Server service

    To use the script, provide the extension with your Azure AD Admin credentials and the Azure AD tenant ID that you copied earlier. Run the script on each NPS server where you installed the NPS extension. Then do the following:

    Configure NPS components on RD Gateway server

    Once you have an NPS server running on your RDS environment, you need to configure the RD Gateway connection authorization policies to work with the NPS server. The authentication flow requires that RADIUS messages be exchanged between the RD Gateway and the NPS server.  This means that RADIUS client settings must be configured on both RD Gateway and NPS server.

    Configure RD Gateway connection authorization policies to use a central store

    Remote Desktop connection authorization policies (RD CAPs) specify the requirements for connecting to a RD Gateway server. By default, RD CAPs are stored locally, and MFA requires that they be stored in a central RD CAP store that is running NPS. Follow the steps below to configure the use of a central store.

    On the RD Gateway server, open Server Manager.

    Configure RADIUS client on RD Gateway NPS

    NPS service

    The NPS server with the NPS extension for Azure needs to be able to exchange messages with the RD Gateway. To enable this message exchange, you need to configure the NPS components on the NPS server.

    Hence you must define an NPS client on the RD Gateway server to allow it to communicate to the NPS server with the NPS extension.

    Configure RADIUS timeout value on RD Gateway NPS

    To ensure there is time to validate users’ credentials, perform two-step verification, receive responses, respond to RADIUS messages, and if necessary, adjust the RADIUS timeout value.

    1. In the NPS (Local) console, expand RADIUS Clients and Servers, and select Remote RADIUS Server Groups. In the details page, double-click TS GATEWAY SERVER GROUP.
    1. Click OK two times to close the dialog boxes.

    Configure connection request policies on RD Gateway 1

    By default, when you configure the RD Gateway to use a central policy store for connection authorization policies, the RD Gateway is configured to forward CAP requests to the NPS server. The NPS server, along with the Azure MFA extension, processes the RADIUS access request. You need to perform the following tasks:

    • Create from MFA policy to determine what happens when you receive a request from the NPS server.
    • Create to MFA policy to determine when to forward a request to the NPS server
    • Disable the default connection request policy.
    Verify policies’ status and processing order.

    Create “From MFA” connection request policy

    Create “To MFA” connection request policy

    Disable default connection request policy

    Verify connection request policies list

    Once you have added the two new policies and disabled the default one, you need to ensure that the policies’ status and processing order are correct. Your policy list should look like the picture below:

    Configure Connection and Resource Authorization policies on RD Gateway 2

    Register server in Active Directory

    For the NPS server to function properly in this scenario, it needs to be registered in Active Directory.

    Create RADIUS client

    The RD Gateway needs to be configured as a RADIUS client to the NPS server.

    Create RADIUS server group

    You need a RADIUS server group to establish communication with the RD Gateway server.

    Create connection request policies

    Just like with the RD Gateway server, you must define policies to handle messaging exchange to/from the RD Gateway server.

    Create “From RD Gateway” connection request policy

    Create “To RD Gateway” connection request policy

     

    Verify connection request policies list

    Once you have added the two new policies, you need to ensure that the policies’ status and processing order are correct. Your policy list should look like the picture below:

    Configure Network Policy

    Because the NPS server with the MFA extension was designated as the central policy store for RD CAPs, you need to implement a new policy on the NPS server to authorize valid connections requests.

    Verify configuration

    To verify the configuration, you need to connect to your RD deployment through the RD Gateway server. Be sure to use an account that is allowed by your RD CAP.

    Open any of the available resources It may ask you to enter your credentials.

     

    References

    The following articles are references used in this design document:

    Title

    Reference

    Azure Active Directory

    https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/active-directory-whatis

    Custom Domain Name

    https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/add-custom-domain

    Integrate your Remote Desktop Gateway infrastructure using the Network Policy Server (NPS) extension and Azure AD

    https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension-rdg

    Remote Desktop Services – Multi-Factor Authentication

    https://docs.microsoft.com/en-us/windows-server/remote/remote-desktop-services/rds-plan-mfa

    Add high availability to the RD Web and Gateway web front

    https://docs.microsoft.com/en-us/windows-server/remote/remote-desktop-services/rds-rdweb-gateway-ha

    Remote Desktop Services – High availability

    https://docs.microsoft.com/en-us/windows-server/remote/remote-desktop-services/rds-plan-high-availability

    Integrate your existing NPS infrastructure with Azure Multi-Factor Authentication

    https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension

    END OF DOCUMENT

By 3tallah

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