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 RRAS Internal Interface Non-Operational

Windows 10 Always On VPN Routing Configuration

Always On VPN administrators troubleshooting connectivity issues may find the Internal network interface in the Routing and Remote Access management console (rrasmgmt.msc) administrative status indicates ‘Unknown’. They will also notice the Operational Status shows Non-operational.

Internal Interface

For clarification, the ‘Internal’ network interface in the Routing and Remote Access management console, as shown above, is not a physical network adapter on the server. Instead, it is a virtual network interface used only for incoming VPN connections.

Non-Operational

The Internal virtual network interface will not be created until the VPN server accepts its first VPN connection. Because of this, the Internal interface will have an operational status of non-operational until the first client attempts to connect. When this occurs, RRAS creates the interface, then assigns it the first IP address from the static IPv4 address pool. Alternatively, if DHCP is configured, it will assign the first IP address returned by the DHCP server.

Interface Names

While discussing network interfaces, I typically recommend renaming them in Windows to identify their function, especially when using two NIC configurations. However, be careful not to name the server’s internal network adapter ‘Internal’, as this can be confusing in the future. In my example above, I use the name ‘LAN’ to identify the internal adapter to distinguish it from the server’s ‘Internal’ virtual interface.

Additional Information

Windows Server RRAS Service Does Not Start

Windows Server RRAS Monitoring and Reporting

Microsoft Always On VPN and RRAS in Azure

Microsoft Always On VPN and RRAS with Signle NIC

Always On VPN Training at TechMentor Redmond 2019

TechMentor Redmond 2019I’m pleased to announce that I’ll be delivering two technical training sessions at this year’s TechMentor Redmond event. This event takes place on the Microsoft campus in Redmond, WA August 5-9, 2019. I’ll be presenting two sessions on Thursday, August 8. They are:

TH16 – Wireshark Essentials: Your First Day with Wireshark

During this session you will learn essential techniques for optimizing packet analysis using Wireshark. Topics will include filter and display tips, workspace oganization, using shortcuts for common tools, and configuring Wireshark profiles. I’ll also touch upon some advanced techniques such as graphing and geography database integration.

TH20 – Always On VPN: The Good, the Bad, and the Ugly!

During this session you will gain a full understanding of Always On VPN including and how it compares with its predecessor, DirectAccess. I’ll share detailed information about this new technology, and how it best fits in to your organizations mobility strategy. Always On VPN has some important advantages over DirectAccess, and some challenging drawbacks. I’ll explain everything good, bad, and even the ugly.

TechMentor Redmond 2019

 

Don’t miss out on this fantastic event. Register now to take advantage of early bird savings, which end June 7. Hope to see you there!