Always On VPN and IPv6

Internet Protocol version 6 (IPv6) has been with us for nearly 30 years. IPv6 adoption on the public Internet has steadily increased over the last decade, and today is approaching 50%. However, enterprise adoption of IPv6 has been surprisingly sluggish despite its numerous benefits. IPv6 includes an expanded address space that removes complex subnetting requirements and globally unique addressing that eliminates the need to perform Network Address Translation (NAT), among others. Organizations should consider deploying IPv6 internally to take advantage of these capabilities.

IPv6 and RRAS

I’ve deployed Microsoft Always On VPN for customers using IPv6 numerous times. The following describes configuration settings required to support IPv6 in a Microsoft environment using a Windows Server Routing and Remote Access (RRAS) server.

To begin, open the Routing and Remote Access management console (rrasmgmt.msc) on the RRAS VPN server, then follow the steps below to enable IPv6 support for Always On VPN connections.

Note: The configuration below assumes that IPv6 is already deployed on the internal network, either natively or dual-stacked with IPv4.

IPv6 Remote Access

Perform the following steps to enable IPv6 remote access on the RRAS VPN server.

  1. Right-click the RRAS VPN server in the navigation tree and choose Properties.
  2. Check the box next to the IPv6 Remote access server on the General tab.

Prefix Assignment

Next, an IPv6 prefix must be assigned to each RRAS VPN server. This IPv6 prefix must be unique for each server and not in use anywhere else on the internal network. Unlike IPv4, IPv6 addresses cannot be assigned from the same prefix (subnet) as the VPN server’s internal network interface. With that, ensure that internal network IPv6 routing returns traffic for the assigned IPv6 prefixes to the corresponding VPN server.

Perform the following steps to assign an IPv6 prefix for VPN client use.

  1. Right-click the RRAS VPN server in the navigation tree and choose Properties.
  2. Select the IPv6 tab.
  3. Check the box next to Enable IPv6 Forwarding.
  4. If force tunneling is required (not recommended), check the box next to Enable Default Route Advertisement.
  5. Enter an IPv6 prefix in the IPv6 prefix assignment field. Again, ensure the IPv6 prefix is globally unique, and that internal network routing is configured to return traffic to the VPN server that owns the prefix.
  6. If your RRAS server is multi-homed, select the internal network interface from the Adapter drop-down list.

DHCP

Organizations with IPv6 deployed internally may use Microsoft Windows DHCPv6 or a dedicated DNS/DHCP/IP Address Management (IPAM) (DDI) solution like Infoblox. However, Windows Server RRAS does not support DHCPv6 for VPN client IP address assignment. Administrators must manually assign an IPv6 prefix per server. However, administrators can use DHCP alongside IPv6 prefix assignment for VPN client IPv4 addressing.

Limitations

While IPv6 may solve some problems for Always On VPN administrators, it has some limitations. Here are some crucial considerations for IPv6 and Always On VPN at the time of this writing.

Traffic Filters

You cannot use IPv6 when configuring traffic filters for Always On VPN. Specifying IPv6 elements in a traffic filter rule will prevent Always On VPN from working at all. More details here.

Intune and Routing

When split tunneling is enabled, Microsoft Intune will not accept IPv6 routes using the standard IPv6 subnet prefix of /64. The UI complains that “the value must be between 1 and 32”.

You can use the custom XML deployment option to configure Always On VPN to support split tunneling correctly as a workaround.

Additional Information

Overview of IPv6

Everything You Never Knew about NAT

Disabling IPv6 Breaks Windows Server RRAS

Microsoft Always On VPN Traffic Filters and IPv6

Discussing Microsoft and IPv6 on the IPv6 Buzz Podcast (Packet Pushers)

Always On VPN Disconnects in Windows 11

Always On VPN administrators migrating their endpoints to Windows 11 may encounter a scenario where Always On VPN randomly disconnects when the VPN profile is deployed using Microsoft Intune. The same configuration deployed to Windows 10 devices works reliably, however. In addition, Always On VPN profiles deployed using PowerShell (natively or with SCCM) or PowerON DPC do not experience this problem.

Troubleshooting

Administrators troubleshooting this issue will find the root cause is associated with the Always On VPN profiles being removed and replaced each time the device syncs with Intune. This occurs even if there are no changes to the configuration. Removing and replacing the Always On VPN profiles on each device sync is unnecessary, of course, but is also highly disruptive to connected users.

Intune and XML

The Intune team identified the issue, and a fix was made available in the August update. However, many of you have reported the issue persists with some Windows 11 clients after installing the latest updates. Further investigation indicates that although the issue has been resolved when using Intune and the native VPN device configuration profile template, the problem still occurs when using the Custom device configuration template.

Workaround

Microsoft is aware of the issues with deploying Always On VPN client configuration settings using XML in Intune, but there’s no indication when or if they will fix it. Until then, administrators have two options to address this problem.

Native VPN Template

When deploying Always On VPN client configuration settings to Windows 11 endpoints, use the native VPN device configuration template, as shown here.

Using the native VPN template does have some limitations, however. The following settings are not exposed using the native VPN template and can only be configured using XML.

XML

If you must use XML, I’ve had some success by ensuring the order of XML settings is exactly as Intune expects. Follow the steps below to confirm the XML settings order in your XML configuration file.

  1. Deploy your XML file with Intune.
  2. Run Get-VpnClientProfileXML.ps1 to extract the deployed XML settings.
  3. Compare the order of settings to your existing XML.
  4. Make changes to ensure all settings in your XML are in the same order as the extracted XML.
  5. Publish a new XML configuration file using Intune and test.

I’ll caution you that this workaround doesn’t always work reliably. Some customers report that this solved their problems entirely, while others have indicated it does not. My testing shows the same results. Let us know in the comments below if this works for you!

Additional Information

Always On VPN Windows 11 Issues with Intune

Always On VPN PowerShell Script Issues in Windows 11

What’s New in Always On VPN DPC v3.0

Recently I wrote about a compelling solution from PowerON Platforms for managing Always On VPN client configuration setting using Active Directory group policy. Always On VPN Dynamic Profile Configurator (DPC) addresses a very specific need for managing Always On VPN for organizations that have not yet migrated to Microsoft Endpoint Manager/Intune. Recently, PowerON Platforms released an important update to DPC that includes many new features and capabilities.

New Features

Always On VPN DPC version 3.0 includes the following new functionality Always On VPN administrators are sure to find useful.

  • Traffic filters – Support for enabling traffic filters for both device tunnel and user tunnel are now supported in DPC, greatly simplifying the task of creating access control lists to enforce zero-trust network access (ZTNA) policies.
  • Enhanced security – The option to disconnect the VPN connection if the VPN server does not present a cryptobinding TLV is now enabled by default. This often-overlooked security setting ensures VPN client connections are not intercepted by detecting man-in-the-middle attacks.
  • Device tunnel enhancements – Administrators can now display the device tunnel connection and status in the Windows UI.
  • Backup connection – Always On VPN DPC now supports the configuration and deployment of a backup VPN connection, which is helpful when Always On VPN connectivity is disrupted.
  • Hostname routing – Administrators can now define hostnames in the routing table. Hostnames are resolved on the endpoint and converted to IP addresses for including in the routing table.
  • Smart card authentication – Always On VPN DPC now supports smart card authentication as an authentication option in addition to client authentication certificates.

Learn More

Interested in learning more about Always On VPN DPC? Fill out the form below and I’ll provide you with additional information or visit aovpndpc.com to sign up for a free trial.

Additional Information

Always On VPN with Active Directory Group Policy

Always On VPN Video Demonstration

Always On VPN DPC Advanced Features

Always On VPN DPC on YouTube