Always On VPN Servers and Failover

When configuring Microsoft Always On VPN, one of the first and most crucial settings is defining the public hostname of the VPN server to which clients connect. If you’re deploying Always On VPN client configuration settings using Intune—either with the native VPN policy template or a custom XML profile—you’ll see that multiple server entries are supported. Intune even allows administrators to define a “default server.” At first glance, this might suggest that the client will try the default server first and automatically fail over to the others if it’s unavailable. Unfortunately, that’s not how it works.

Intune VPN Template

When using the native Intune VPN device configuration template, administrators will find multiple entry fields for the servers in the Base VPN section.

In the example below, the Global VPN entry is marked as ‘default’.

Custom XML

When defining VPN settings using XML configuration, administrators can also list multiple servers.

Interestingly, the VPNv2 CSP used by custom XML profiles doesn’t support the concept of a “default server” at all.

How It Really Works

Defining multiple servers in the Always On VPN profile does not enable automatic failover. The client connects only to the first server in the list. The so-called “default server” setting in Intune is ignored, and the GUI even allows you to mark all servers as default, which is meaningless.

However, the configuration isn’t entirely useless. If you define multiple servers, they’ll appear on the client side as manual options. If the first server becomes unavailable, the user can open the Settings app, navigate to the advanced settings of the Always On VPN profile, and select an alternate server to connect manually.

Summary

Although Intune and XML configurations allow multiple VPN servers, Always On VPN does not provide automatic failover. Clients only attempt to connect to the first server in the list, and the “default server” setting in Intune has no effect. Multiple entries are still useful, but only for manual server selection by end-users when the primary server is down. For true automated high availability and redundancy, consider an external solution such as Azure Traffic Manager.

Additional Information

Always On VPN Multisite with Azure Traffic Manager

Always On VPN Load Balancing with Loadbalancer.org

Recently, I had the opportunity to deploy the Loadbalancer.org load balancer as part of an enterprise Always On VPN deployment. In the past, I’ve published guidance for using F5 BIG-IP, Citrix ADC (formerly NetScaler), and Kemp LoadMaster, so in this post, I’ll provide guidance for configuring Loadbalancer.org for Always On VPN.

IKEv2

Open the Loadbalancer.org management console and follow the steps below to configure Always On VPN load balancing on the appliance.

Create Virtual Service

Create a layer 4 virtual service for IKEv2.

  1. Click Cluster Configuration.
  2. Click Layer 4 – Virtual Services.
  3. Click Add a new Virtual Service.
  4. Enter a descriptive name for the virtual service in the Label field.
  5. Enter the virtual IP address (VIP) for the service in the IP Address field.
  6. Enter 500,4500 in the Ports field.
  7. Select UDP from the Protocol drop-down list.
  8. Select NAT from the Forwarding Method drop-down list.
  9. Click Update.

Add Real Servers

Add real servers to the virtual service.

  1. Click Layer 4 – Real Servers.
  2. Click Add a new Real Server next to the IKEv2 virtual service.
  3. Enter a descriptive name for the real server in the Label field.
  4. Enter the IP address of the real server in the Real Server IP Address field.
  5. Click Update.
  6. Repeat these steps for each additional VPN server in the cluster.

SSTP

Follow the steps below to configure SSTP load balancing on the appliance.

Create Virtual Service

Create a layer 4 virtual service for SSTP.

  1. Click Cluster Configuration.
  2. Click Layer 4 – Virtual Services.
  3. Click Add a new Virtual Service.
  4. Enter a descriptive name for the virtual service in the Label field.
  5. Enter the virtual IP address (VIP) for the service in the IP Address field.
  6. Enter 443 in the Ports field.
  7. Select TCP from the Protocol drop-down list.
  8. Select NAT from the Forwarding Method drop-down list.
  9. Click Update.

Configure Virtual Service Health Check

Update the health check method for the SSTP virtual service.

  1. Click Layer 4 – Virtual Services.
  2. Click Modify on the SSTP virtual service.
  3. Select Negotiate from the Check Type drop-down list in the Health Checks section.
  4. Enter 443 in the Check Port field.
  5. Select HTTPS from the Protocol drop-down list.
  6. Enter /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ in the Request to send field.
  7. Enter 401 in the Response expected field.
  8. Click Update.

Note: Using the Negotiate health check type for the SSTP monitor on Loadbalancer.org appliances requires version 8.13.0 or later. Administrators can use the External script option when using earlier releases of Loadbalancer.org appliances. An SSTP health check script for Loadbalancer.org can be found here.

Add Real Servers

Add real servers to the virtual service.

  1. Click Layer 4 – Real Servers.
  2. Click Add a new Real Server next to the SSTP virtual service.
  3. Enter a descriptive name for the real server in the Label field.
  4. Enter the IP address of the real server in the Real Server IP Address field.
  5. Click Update.
  6. Repeat these steps for each additional VPN server in the cluster.

Review

Once complete, click System Overview to view the overall health of your VPN servers.

Summary

The Loadbalancer.org appliance is an efficient, cost-effective, and easy-to-configure load-balancing solution that works well with Always On VPN implementations. It’s available as a physical or virtual appliance. There’s also a cloud-based version. It also includes advanced features such as TLS offload, web application firewall (WAF), global server load balancing (GSLB), and more. If you are looking for a layer 4-7 load balancer for Always On VPN and other workloads, be sure to check them out.

Additional Information

Loadbalancer.org Virtual Appliance

SSTP Health Check Script for Loadbalancer.org

Always On VPN and VpnStrategy

NetMotion Mobility for DirectAccess Administrators – Split vs. Force Tunneling

Always On VPN supports a variety of VPN protocols for the user tunnel. Internet Key Exchange version 2 (IKEv2) and Secure Socket Tunneling Protocol (SSTP) are the most common. I wrote about the advantages and disadvantages of each in this post. To summarize, IKEv2 provides the highest security options but suffers from operational limitations. SSTP offers excellent security and is generally more reliable.

VpnStrategy

Always On VPN administrators must choose between IKEv2 and SSTP when configuring the Always On VPN user tunnel. Some administrators may prefer to use IKEv2 when available but then fall back to SSTP if it is not. To accomplish this requires editing the rasphone.pbk file and setting the value of VpnStrategy to 8, as described here.

Challenges

Unfortunately, setting the VpnStrategy value to 8 poses some challenges. Updating rasphone.pbk requires editing a text file on each endpoint post-deployment. Updating rasphone.pbk can be automated using the Update-Rasphone.ps1 script or Microsoft Intune proactive remediation.

Limitations

By default, Windows will overwrite the VpnStrategy setting in rasphone.pbk when fallback occurs. For example, setting VpnStrategy to prefer IKEv2 over SSTP will be reset to use SSTP first if a connection with IKEv2 fails. There’s a registry setting available that’s supposed to prevent this, but it doesn’t always work as expected.

Windows 11

There’s good news for administrators deploying Always On VPN on Windows 11. Microsoft recently introduced support for additional NativeProtocol types in XML. Specifically, VPN protocol preference can now be defined using the ProtocolList native protocol type. When using the ProtocolList native protocol type, each supported VPN protocol is listed in order of preference using the syntax shown below.

In addition, the RetryTimeInHours value defines the time Windows will try the last successful connection protocol. Setting this value to 0 overrides this and ensures the preferred protocol (the first protocol in the list) will always be attempted first.

SSTP Only

Previously the VPNv2CSP only supported IKEv2 or Automatic as values for the native protocol type. Windows 11 now supports SSTP as a native protocol type. Administrators configuring Always On VPN user tunnel connections using SSTP exclusively can now use this option.

Caveats

While the settings above are supported in both Windows 11 21H2 and 22H2, there are some known issues when enabling these settings. Specifically, when administrators define the ProtocolList value for the native protocol type, IKEv2 is always shown as the active protocol, even when an SSTP connection is established.

Also, if ProtocolList is used, the VPN connection cannot be managed using PowerShell. The VPN profile will not be displayed when running Get-VpnConnection at the time of this writing. Hopefully Microsoft will fix this soon.

Additional Information

Always On VPN CSP Updates

Always On VPN IKEv2 and SSTP Fallback

Always On VPN and Intune Proactive Remediation

Always On VPN Protocol Recommendations for Windows Server RRAS

Always On VPN IKEv2 Features and Limitations