Deploying DirectAccess in Microsoft Azure

Introduction

DirectAccess Now a Supported Workload in Microsoft AzureMany organizations are preparing to implement DirectAccess on Microsoft’s public cloud infrastructure. Deploying DirectAccess in Azure is fundamentally no different than implementing it on premises, with a few important exceptions (see below). This article provides essential guidance for administrators to configure this unique workload in Azure.

Important Note: There has been much confusion regarding the supportability of DirectAccess in Azure. Historically it has not been supported. Recently, it appeared briefly that Microsoft reversed their earlier decision and was in fact going to support it. However, the Microsoft Server Software Suport for Microsoft Azure Virtual Machines document has once again been revised to indicate that DirectAccess is indeed no longer formally supported on Azure. More details can be found here.

Azure Configuration

The following is guidance for configuring network interfaces, IP address assignments, public DNS, and network security groups for deploying DirectAccess in Azure.

Virtual Machine

Deploy a virtual machine in Azure with sufficient resources to meet expected demand. A minimum of two CPU cores should be provisioned. A VM with 4 cores is recommended. Premium storage on SSD is optional, as DirectAccess is not a disk intensive workload.

Network Interfaces

It is recommended that an Azure VM with a single network interface be provisioned for the DirectAccess role. This differs from on-premises deployments where two network interfaces are preferred because deploying VMs in Azure with two NICs is prohibitively difficult. At the time of this writing, Azure VMs with multiple network interfaces can only be provisioned using PowerShell, Azure CLI, or resource manager templates. In addition, Azure VMs with multiple NICs cannot belong to the same resource group as other VMs. Finally, and perhaps most importantly, not all Azure VMs support multiple NICs.

Internal IP Address

Static IP address assignment is recommended for the DirectAccess VM in Azure. By default, Azure VMs are initially provisioned using dynamic IP addresses, so this change must be made after the VM has been provisioned. To assign a static internal IP address to an Azure VM, open the Azure management portal and perform the following steps:

  1. Click Virtual machines.
  2. Select the DirectAccess server VM.
  3. Click Network Interfaces.
  4. Click on the network interface assigned to the VM.
  5. Under Settings click IP configurations.
  6. Click Ipconfig1.
  7. In the Private IP address settings section choose Static for the assignment method.
  8. Enter an IP address for the VM.
  9. Click Save.

Deploying DirectAccess in Microsoft Azure

Public IP Address

The DirectAccess VM in Azure must have a public IP address assigned to it to allow remote client connectivity. To assign a public IP address to an Azure VM, open the Azure management portal and perform the following steps:

  1. Click Virtual machines.
  2. Select the DirectAccess server VM.
  3. Click Network Interfaces.
  4. Click on the network interface assigned to the VM.
  5. Under Settings click IP configurations.
  6. Click Ipconfig1.
  7. In the Public IP address settings section click Enabled.
  8. Click Configure required settings.
  9. Click Create New and provide a descriptive name for the public IP address.
  10. Choose an address assignment method.
  11. Click Ok and Save.

Deploying DirectAccess in Microsoft Azure

Deploying DirectAccess in Microsoft Azure

Public DNS

If the static IP address assignment method was chosen for the public IP address, create an A resource record in public DNS that resolves to this address. If the dynamic IP address assignment method was chosen, create a CNAME record in public DNS that maps to the public hostname for the DirectAccess server. To assign a public hostname to the VM in Azure, open the Azure management portal and perform the following steps:

  1. Click Virtual machines.
  2. Select the DirectAccess server VM.
  3. Click Overview.
  4. Click Public IP address/DNS name label.Deploying DirectAccess in Microsoft Azure
  5. Under Settings click Configuration.
  6. Choose an assignment method (static or dynamic).
  7. Enter a DNS name label.
  8. Click Save.

Deploying DirectAccess in Microsoft Azure

Note: The subject of the SSL certificate used for the DirectAccess IP-HTTPS listener must match the name of the public DNS record (A or CNAME) entered previously. The SSL certificate does not need to match the Azure DNS name label entered here.

Network Security Group

A network security group must be configured to allow IP-HTTPS traffic inbound to the DirectAccess server on the public IP address. To make the required changes to the network security group, open the Azure management portal and perform the following steps:

  1. Click Virtual machines.
  2. Select the DirectAccess server VM.
  3. Click Network interfaces.
  4. Click on the network interface assigned to the VM.
  5. Under Settings click Network security group.
  6. Click the network security group assigned to the network interface.
  7. Click Inbound security rules.
  8. Click Add and provide a descriptive name for the new rule.
  9. Click Any for Source.
  10. From the Service drop-down list choose HTTPS.
  11. Click Allow for Action.
  12. Click Ok.

Deploying DirectAccess in Microsoft Azure

Note: It is recommended that the default-allow-rdp rule be removed if it is not needed. At a minimum, scope the rule to allow RDP only from trusted hosts and/or networks.

DirectAccess Configuration

When performing the initial configuration of DirectAccess using the Remote Access Management console, the administrator will encounter the following warning message.

“One or more network adapters should be configured with a static IP address. Obtain a static address and assign it to the adapter.”

Deploying DirectAccess in Microsoft Azure

This message can safely be ignored because Azure infrastructure handles all IP address assignment for hosted VMs.

The public name of the DirectAccess server entered in the Remote Access Management console must resolve to the public IP address assigned to the Azure VM, as described previously.

Deploying DirectAccess in Microsoft Azure

Additional Considerations

When deploying DirectAccess in Azure, the following limitations should be considered.

Load Balancing

It is not possible to enable load balancing using Windows Network Load Balancing (NLB) or an external load balancer. Enabling load balancing for DirectAccess requires changing static IP address assignments in the Windows operating system directly, which is not supported in Azure. This is because IP addresses are assigned dynamically in Azure, even when the option to use static IP address assignment is chosen in the Azure management portal. Static IP address assignment for Azure virtual machines are functionally similar to using DHCP reservations on premises.

Deploying DirectAccess in Microsoft Azure

Note: Technically speaking, the DirectAccess server in Azure could be placed behind a third-party external load balancer for the purposes of performing SSL offload or IP-HTTPS preauthentication, as outlined here and here. However, load balancing cannot be enabled in the Remote Access Management console and only a single DirectAccess server per entry point can be deployed.

Manage Out

DirectAccess manage out using native IPv6 or ISATAP is not supported in Azure. At the time of this writing, Azure does not support IPv6 addressing for Azure VMs. In addition, ISATAP does not work due to limitations imposed by the underlying Azure network infrastructure.

Summary

For organizations moving infrastructure to Microsoft’s public cloud, formal support for the DirectAccess workload in Azure is welcome news. Implementing DirectAccess in Azure is similar to on-premises with a few crucial limitations. By following the guidelines outlined in this article, administrators can configure DirectAccess in Azure to meet their secure remote access needs with a minimum of trouble.

Additional Resources

Implementing DirectAccess in Windows Server 2016
Fundamentals of Microsoft Azure 2nd Edition
Microsoft Azure Security Infrastructure
DirectAccess Multisite with Azure Traffic Manager
DirectAccess Consulting Services

DirectAccess IP-HTTPS Preauthentication


Introduction

DirectAccess IP-HTTPS PreauthenticationRecently I’ve written about the security challenges with DirectAccess, specifically around the use of the IP-HTTPS IPv6 transition technology. In its default configuration, the DirectAccess server does not authenticate the client when an IP-HTTPS transition tunnel is established. This opens up the possibility of an unauthorized user launching Denial-of-Service (DoS) attacks and potentially performing network reconnaissance using ICMPv6. More details on this can be found here.

Mitigation

The best way to mitigate these security risks is to implement an Application Delivery Controller (ADC) such as the F5 BIG-IP Local Traffic Manager or the Citrix NetScaler. I’ve documented how to configure those platforms here and here.

No ADC?

For those organizations that do not have a capable ADC deployed, it is possible to configure the IP-HTTPS listener on the Windows Server 2012 R2 server itself to perform preauthentication.

Important Note: Making the following changes on the DirectAccess server is not formally supported. Also, this change is incompatible with one-time passwords (OTP)  and should not be performed if strong user authentication is enabled. In addition, null cipher suites will be disabled, resulting in reduced scalability and degraded performance for Windows 8.x and Windows 10 clients. Making this change should only be done if a suitable ADC is not available.

Configure IP-HTTPS Preauthentication

To configure the DirectAccess server to perform preauthentication for IP-HTTPS connections, open an elevated PowerShell command window and enter the following command.

ls Cert:\LocalMachine\My

DirectAccess IP-HTTPS Preauthentication

Copy the thumbprint that belongs to the SSL certificate assigned to the IP-HTTPS listener. Open an elevated command prompt window (not a PowerShell window!) and enter the following commands.

netsh http delete sslcert ipport=0.0.0.0:443
netsh http add sslcert ipport=0.0.0.0:443 certhash=[thumbprint]
appid={5d8e2743-ef20-4d38-8751-7e400f200e65}
dsmapperusage=enable clientcertnegotiation=enable

DirectAccess IP-HTTPS Preauthentication

For load-balanced clusters and multisite deployments, repeat these steps on each DirectAccess server in the cluster and/or enterprise.

Summary

Once these changes have been made, only DirectAccess clients that have a computer certificate with a subject name that matches the name of its computer account in Active Directory will be allowed to establish an IP-HTTPS transition tunnel connection.

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IP

Note: For information about configuring the Citrix NetScaler to perform IP-HTTPS preauthentication, click here. For information about configuring Windows Server 2012 R2 to perform IP-HTTPS preauthentication natively, click here.

Introduction

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IPRecently I wrote about security challenges with DirectAccess and the IP-HTTPS IPv6 transition technology. Specifically, IP-HTTPS transition tunnel connections are not authenticated by the DirectAccess server, only the client. This allows an unauthorized device to obtain an IPv6 address on the DirectAccess client network. With it, an attacker can perform network reconnaissance using ICMPv6 and potentially launch a variety of Denial-of-Service (DoS) attacks. For more details, click here.

Note: DirectAccess IPsec data connections not at risk. Data is never exposed at any time with the default configuration.

Mitigation

To mitigate these issues, it is recommended that an Application Delivery Controller (ADC) be used to terminate SSL connections and enforce client certificate authentication. Doing this will ensure that only authorized connections will be accepted by the DirectAccess server. In addition, there are some scalability and performance benefits to implementing this configuration when supporting Windows 7 clients.

Important Considerations

Performing IP-HTTPS preauthentication on the F5 BIG-IP is formally unsupported by Microsoft. In addition, terminating IP-HTTPS on the F5 appliance breaks OTP authentication.

F5 BIG-IP Configuration

To configure the F5 BIG-IP to perform SSL offload for DirectAccess IP-HTTPS, follow the guidance documented here. In addition, to configure the F5 BIG-IP to perform preauthentication for DirectAccess clients, when creating the client SSL profile, click Custom above the Client Authentication section and choose Require from the Client Certificate drop-down list and Always from the Frequency drop-down list. In addition, choose your internal PKI’s root Certification Authority (CA) certificate from the Trusted Certificate Authorities drop-down list and from the Advertised Certificate Authorities drop-down list.

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IP

Summary

Enabling client certificate authentication for IP-HTTPS connections ensures that only authorized DirectAccess clients can establish a connection to the DirectAccess server and obtain an IPv6 address. It also prevents an unauthorized user from performing network reconnaissance or launching IPv6 Denial-of-Service (DoS) attacks.

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