Always On VPN IKEv2 Features and Limitations

Always On VPN IKEv2 Features and LimitationsThe Internet Key Exchange version 2 (IKEv2) VPN protocol is a popular choice for Windows 10 Always On VPN deployments. IKEv2 is a standards-based IPsec VPN protocol with customizable security parameters that allows administrators to provide the highest level of protection for remote clients. In addition, it provides important interoperability with a variety of VPN devices, including Microsoft Windows Server Routing and Remote Access Service (RRAS) and non-Microsoft platforms such as Cisco, Checkpoint, Palo Alto, and others.

IKEv2 Limitations

IKEv2 is clearly the protocol of choice in terms of security. It supports modern cryptography and is highly resistant to interception. It’s not without some operational challenges, however. Consider the following.

Firewalls

IKEv2 uses UDP ports 500 and 4500 for communication. Unfortunately, these ports are not always open. Often, they are blocked by network administrators to prevent users from bypassing security controls or attackers from exfiltrating data.

Fragmentation

IKEv2 packets can become quite large at times, especially when using client certificate authentication with the Protected Extensible Authentication Protocol (PEAP). This can result in fragmentation occurring at the network layer. Unfortunately, many firewalls and network devices are configured to block IP fragments by default. This can result in failed connection attempts from some locations but not others.

Load Balancing

Load balancing IKEv2 connections is not entirely straightforward. Without special configuration, load balancers can cause intermittent connectivity issues for Always On VPN connections. Guidance for configuring IKEv2 load balancing on the Kemp LoadMaster and the F5 BIG-IP can be found here:

IKEv2 Fragmentation

IKEv2 fragmentation can be enabled to avoid IP fragmentation and restore reliable connectivity. IKEv2 fragmentation is supported in Windows 10 and Windows Server beginning with v1803. Guidance for enabling IKEv2 fragmentation on Windows Server RRAS can be found here. Support for IKEv2 fragmentation on non-Microsoft firewall/VPN devices is vendor-specific. Consult with your device manufacturer for more information.

IKEv2 Security and RRAS

Be advised that the default security settings for IKEv2 on Windows Server RRAS are very poor. The minimum recommended security settings and guidelines for implementing them can be found here.

IKEv2 or TLS?

IKEv2 is recommend for deployments where the highest level of security and protection is required for remote connections. In these scenarios, the sacrifice of ubiquitous availability in favor of ultimate security might be desired.

SSTP or another TLS-based VPN protocol is recommended if reliable operation and connectivity are desired. SSTP and TLS VPNs can be configured to provide very good security by following the security and implementation guidelines found here.

IKEv2 with TLS Fallback

In theory, preferring IKEv2 and falling back to the Secure Socket Tunneling Protocol (SSTP) or another TLS-based VPN protocol when IKEv2 is unavailable would seem like a logical choice. This would ensure the highest level of protection, while still providing reliable connectivity. Unfortunately, the Windows VPN client doesn’t work this way in practice. Details here.

Additional Information

Windows 10 Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Windows 10 Always On VPN IKEv2 Load Balancing with Kemp LoadMaster

Windows 10 Always On VPN IKEv2 Fragmentation

Windows 10 Always On VPN IKEv2 and SSTP Fallback

Windows 10 Always On VPN IKEv2 Security Configuration

Windows 10 Always On VPN Certificate Requirements for IKEv2

Windows 10 Always On VPN Protocol Recommendations for Windows Server RRAS

Always On VPN SSTP Connects then Disconnects

Always On VPN SSTP Connects then DisconnectsWhen Always On VPN clients are configured to use the Secure Socket Tunneling Protocol (SSTP) with Windows Server Routing and Remote Access Service (RRAS), administrators may encounter a scenario in which a client can establish a VPN connection using SSTP successfully, but is then disconnected immediately. The system event log contains an entry with Event ID 6 from the RasSstp source that includes the following error message.

“The SSTP-based VPN connection to the remote access server was terminated because of a security check failure. Security settings on the remote access server do not match settings on this computer. Contact the system administrator of the remote access server and relay the following information.”

Always On VPN Connect and Disconnect with SSTP

Common Causes

The two most common causes of this issue are when SSTP is configured for SSL offload, and when a VPN client is on a network where SSL inspection is taking place.

SSTP Offload

The most common cause of this issue is when SSL offload is configured for SSTP on an external load balancer or application delivery controller (ADC). To prevent interception from a Man-in-the-Middle attack, the VPN client sends the certificate hash of the SSL certificate used when the VPN connection was established. If this information does not match what is configured on the RRAS server, the connection is assumed to be compromised and the connection is immediately dropped.

SSL Inspection

Another scenario where this issue may occur is when a VPN client is behind a network device configured to perform SSL deep-packet inspection (DPI). SSTP VPN clients will be unable to connect to the VPN server in this scenario.

Resolution

When offloading SSL to another device, the RRAS server must be configured to know which SSL certificate is being presented to remote clients. This information is stored in the following registry key.

HKLM:\SYSTEM\CurrentControlSet\Services\SstpSvc\Parameters\SHA256CertificateHash

However, this registry entry requires a binary value, which makes it a challenge to configure manually. To resolve this problem, it is recommended that the same SSL certificate installed on the load balancer/ADC also be installed on the VPN server (even though SSL will be offloaded). To do this, first import the SSL certificate and private key in to the Local Computer certificate store, then open the RRAS management console and perform the following steps.

  1. Right-click the VPN server and choose Properties.
  2. Select the Security tab.
  3. Uncheck Use HTTP in the SSL Certificate Binding section.
  4. Select the appropriate SSL certificate from the Certificate drop-down list (click View to verify).
  5. Click Apply.

This will add the correct SSL certificate information to the registry. Next, re-enable HTTP for SSL offload by performing the following steps.

  1. Check Use HTTP in the SSL Certificate Binding section.
  2. Click Apply.

PowerShell Configuration

If the SSL certificate cannot be installed on the VPN server, or to automate this configuration across multiple servers remotely, download and run the Enable-SstpOffload PowerShell script from my GitHub repository here and run the following command.

Enable-SSTPOffload -CertificateHash [SHA256 Certificate Hash of Public SSL Certificate] -Restart

For example…

Enable-SSTPOffload -CertificateHash “C3AB8FF13720E8AD9047DD39466B3C8974E592C2FA383D4A3960714CAEF0C4F2” -Restart

Additional Information

Windows 10 Always On VPN Load Balancing and SSL Offload

Windows 10 Always On VPN SSL Certificate Requirements for SSTP

Windows 10 Always On VPN Protocol Recommendations for Windows Server RRAS

Always On VPN SSTP Load Balancing and SSL Offload

SSL Certificate Considerations for DirectAccess IP-HTTPSThe Windows Server Routing and Remote Access Service (RRAS) is a popular choice for a VPN server to support Windows 10 Always On VPN deployments. One significant advantage RRAS provides is support for the Secure Socket Tunneling Protocol (SSTP). SSTP is a Microsoft proprietary VPN protocol that uses Transport Layer Security (TLS) to ensure privacy between the VPN client and server. The advantage to using a TLS-based transport is that it leverages the standard HTTPS TCP port 443, making it firewall friendly and ensuring ubiquitous remote access even behind highly restrictive firewalls.

Load Balancing SSTP

Load balancing SSTP can be accomplished in much the same way as a load balancing a common web server using HTTPS. The external load balancer is configured with a virtual IP address (VIP) and each VPN server is configured behind it. Session persistence should be configured to use SSL with source IP address persistence as a fallback.

SSL Offload for SSTP

In most cases, simply forwarding encrypted SSTP connections to the VPN server will be sufficient. However, offloading SSL/TLS processing to an Application Delivery Controller (ADC) or load balancer can be beneficial for the following reasons.

Resource Utilization

Enabling TLS offload for SSTP VPN connections can reduce CPU and memory utilization on the VPN server. However, this will likely only be necessary for very busy servers supporting many concurrent connections.

Security

In some cases, the administrator may not be able to install the public SSL certificate on the VPN server. For example, a security policy may exist that restricts SSL certificate installation to dedicated security devices using a Hardware Security Module (HSM). In some cases, it may be desirable to restrict access to high value certificates such as wildcard certificates.

Certificate Management

Often SSL certificates are implemented on load balancers to reduce certificate sprawl and to ease the management and administration burden in the enterprise. By having all enterprise certificates installed only on dedicated security devices, administrators can more effectively monitor and manage SSL certificate lifecycles.

SSTP Configuration for TLS Offload

Configuration changes must be made on the load balancer and the RRAS server to support TLS offload for SSTP.

Load Balancer

Install the public SSL certificate on the load balancer and configure it for TLS termination. Configure the load balancer to then use HTTP for backend server connections. Consult the load balancer vendor’s documentation for configuration guidance.

RRAS Server

If the public SSL certificate is installed on the VPN server, enabling TLS offload for SSTP is simple and straightforward. Follow the steps below to enable TLS offload for SSTP VPN connections.

  1. Open the RRAS management console (rrasmgmt.msc).
  2. Right-click the VPN server and choose Properties.
  3. Select the Security tab.
  4. Check Use HTTP in the SSL Certificate Binding section.
  5. Click Ok and then Yes to restart the Remote Access service.

Always On VPN SSTP Load Balancing and SSL Offload

If the public SSL certificate is not or cannot be installed on the RRAS server, additional configuration will be required. Specifically, SSL offload for SSTP must be configured using the Enable-SSTPOffload PowerShell script, which can be downloaded here.

Once the script has been downloaded and imported, open an elevated PowerShell command window and enter the following command.

Enable-SSTPOffload -CertificateHash [SHA256 Certificate Hash of Public SSL Certificate] -Restart

For example…

Enable-SSTPOffload -CertificateHash “C3AB8FF13720E8AD9047DD39466B3C8974E592C2FA383D4A3960714CAEF0C4F2” -Restart

Re-Encryption

When offloading TLS for SSTP VPN connections, all traffic between the load balancer and the VPN server will be sent in the clear using HTTP. In some scenarios, TLS offload is required only for traffic inspection, not performance gain. When terminating TLS on the load balancer and re-encrypting connections to the VPN server is required, it is only supported if the same certificate is used on both the load balancer and the VPN server.

Additional Information

Windows 10 Always On VPN SSL Certificate Requirements for SSTP

Windows 10 Always On VPN IKEv2 and SSTP Fallback

Windows 10 Always On VPN Hands-On Training Classes for 2019

Always On VPN and Third Party VPN Devices

Always On VPN and Third Party VPN DevicesOne of the most important advantages Windows 10 Always On VPN has over DirectAccess is infrastructure independence. That is, Always On VPN does not rely exclusively on a Windows Server infrastructure to support Always On VPN connections. Always On VPN will work with many third-party firewalls and VPN devices, as long as they meet some basic requirements.

Advantages

Third-party firewalls or VPN devices offer some important advantages over Windows Servers running the Routing and Remote Access Services (RRAS), both in terms of security and performance.

Security

Dedicated security devices (physical or virtual) provide better security than a common Windows server. They commonly run specialized, security-hardened operating systems that are highly secure and resistant to attack. In addition, these solutions typically allow the administrator to define policy to restrict access to internal resources and do so in a centralized way. This is often easier to implement and manage than using traffic filters on the client side. They often include advanced security features such as URL filtering and malware inspection to better protect remote clients. Some solutions include Hardware Security Module (HSM) integration to further enhance security.

Performance

Purpose-built solutions often provide better throughput and performance than do Windows Servers by virtue of their proprietary operating systems. This allows for better network throughput and the ability to support many more connections per device.

Disadvantages

The main drawbacks for using a third-party device are cost and administrative overhead. Third-party solutions must be acquired, for which there is typically a non-trivial cost associated. They often need additional per-user licensing. In addition, many of these solutions require specialized skill sets to implement, manage, and support which could further increase the overall cost of the solution.

Interoperability Requirements

Any firewall or VPN device can be used for Always On VPN as long as they support the Internet Key Exchange version 2 (IKEv2) VPN protocol for remote access connections. Most modern firewalls today support IKEv2, but some (such as the Sophos XG firewall) do not. Check with your vendor to validate support.

Native Client

If the firewall or VPN device supports IKEv2 for remote access connections, the native Windows VPN provider can be used to establish an Always On VPN connection. The native provider is used when the Always On VPN ProfileXML is configured using the NativeProfile element.

Plug-In VPN Client

One crucial drawback to using IKEv2 is that it is commonly blocked by firewalls. Many third-party VPN vendors offer a plug-in client that enables support for TLS-based transport, which is more firewall friendly than IKEv2. Plug-in VPN providers are available in the Microsoft store.

Below is a current list of available third-party VPN plug-in providers for Windows 10. (Updated April 5 to now include Cisco AnyConnect!)

  • Check Point Capsule
  • Cisco AnyConnect
  • F5 Access
  • Fortinet Forticlient
  • Palo Alto GlobalProtect
  • Pulse Secure
  • SonicWall Mobile Connect

Always On VPN and Third-Party VPN Devices

Note: Win32 VPN client applications from third-party vendors are not supported with Windows 10 Always On VPN.

Additional Information

What is the Difference Between DirectAccess and Always On VPN?

5 Things DirectAccess Administrators Should Know about Always On VPN

3 Important Advantages of Always On VPN over DirectAccess

Always On VPN and DirectAccess Scripts and Sample Files on GitHub

Always On VPN and DirectAccess Scripts and Sample Files on GitHubIf you’re looking for specialized configuration scripts for Windows 10 Always On VPN, Windows Server Routing and Remote Access Service (RRAS), or DirectAccess then have a look at my GitHub page! There I’ve uploaded a few tools I’ve created (with the help of my good friend Jeff Hicks!) along with some sample ProfileXML files. Here’s a sample of what you’ll find there today.

Always On VPN

This repository includes PowerShell scripts and sample ProfileXML files used for configuring Windows 10 Always On VPN. These scripts have been adopted from those provided by Microsoft and modified to work with a separate XML file. These scripts can be used for local testing and for deploying Always On VPN connections using System Center Configuration Manager (SCCM). The ProfileXML files can be helpful for those administrators looking for real world configuration examples.

https://github.com/richardhicks/aovpn

SstpOffload

This repository includes a PowerShell script to enable TLS offload for Windows Server RRAS Secure Socket Tunneling Protocol (SSTP) VPN connections when the public SSL certificate can’t be installed on the RRAS server. TLS offload for SSTP can be enabled in scenarios where better security, performance, and scalability are desired.

https://github.com/richardhicks/sstpoffload

DirectAccess

This repository includes the PowerShell script Move-DaInboxAccountingDatabase which can be used to move the DirectAccess inbox accounting database files. The default location of the database files is on the C: drive, and many administrators have encountered disk space issues, especially in large scale deployments. This script will relocate the database files to the location of your choice.

https://github.com/richardhicks/directaccess

More to Come!

Be sure to check my GitHub site for more PowerShell script and sample files on a regular basis. Or better yet, give me a follow! I’ll be sure to post more as time goes on. In addition, I’ll be going through my older articles where I’ve provided PowerShell code samples and will include them in the repository too.

Standard Disclaimer

All the sample files and PowerShell scripts I’ve shared on GitHub are provided as-is. Although they’ve been thoroughly tested, I can’t be certain I’ve accommodated every deployment scenario. Please use caution when running these scripts on production machines.

Additional Information

Always On VPN Hands-On Training Classes 2019

Jeff Hicks’ Blog

Always On VPN IKEv2 and SSTP Fallback

Always On VPN IKEv2 and SSTP FallbackA while back I wrote about the various VPN protocols supported for Windows 10 Always On VPN. The two most common are Internet Key Exchange version 2 (IKEv2) and Secure Socket Tunneling Protocol (SSTP). The article covers in detail each protocol’s advantages and disadvantages. To summarize, IKEv2 provides the best security (when configured correctly!) and SSTP is firewall-friendly ensuring ubiquitous access. Ideally an Always On VPN connection will attempt to use the more secure IKEv2 first, then fallback to SSTP only when IKEv2 is unavailable. Unfortunately, Always On VPN connections do not work this way today.

IKEv2 and SSTP

IKEv2 and SSTP are not mutually exclusive. When using Windows Routing and Remote Access Service (RRAS) as the VPN server, both protocols can be configured and enabled for VPN clients. To allow VPN clients to automatically select a protocol, the NativeProtocolType element in ProfileXML can be set to Automatic.

Always On VPN IKEv2 and SSTP Fallback

IKEv2 with SSTP Fallback?

In theory, with the NativeProtocolType set to Automatic, the Windows 10 client would first attempt to establish an IKEv2 connection, then fall back to SSTP if IKEv2 is not available. In practice, this is not the case.

SSTP Preferred over IKEv2

In operation, setting the NativeProtocolType to Automatic results in the Windows 10 client attempting to establish a VPN connection using SSTP first! If the SSTP connection fails, only then will IKEv2 be used. The only scenario in which I can imagine SSTP failing and IKEv2 being successful would be if SSTP is not supported by the VPN server. Sadly, this scenario may result in failed connections due to a bug in the way ProfileXML settings are processed. Details here.

VPN Strategy

The initial VPN protocol selection behavior is dictated by the VpnStrategy setting of the Always On VPN connection in the rasphone.pbk file. This file can be found under C:\Users\[username]\AppData\Roaming\Microsoft\Network\Connections\Pbk. The documentation on the Microsoft website is terribly outdated and does not include the following important VpnStrategy settings pertinent to Windows 10 Always On VPN connections.

  • 5 = Only SSTP is attempted
  • 6 = SSTP is attempted first
  • 7 = Only IKEv2 is attempted
  • 8 = IKEv2 is attempted first
  • 14 = IKEv2 is attempted followed by SSTP

Always On VPN Default Behavior

For Always On VPN, when the NativeProtocolType is set to Automatic in ProfileXML, VpnStrategy is set to 6 by default, which means the connection will attempt to use SSTP first. If it fails, IKEv2 will be attempted.

Always On VPN IKEv2 and SSTP Fallback

If the NativeProtocolType in ProfileXML is set to IKEv2, VpnStrategy is set to 7 and only IKEv2 is used. A connection using SSTP is never attempted.

Workaround

Setting the VpnStrategy to 8 or 14 will force the client to attempt an IKEv2 connection first. However, this setting is dynamically updated by Windows and is subject to change. For example, if an IKEv2 connection fails and SSTP is successful, Windows will then set the VpnStrategy to 6 and all subsequent VPN connection attempts will use SSTP first. Because of this it will be necessary to update the VpnStrategy setting each time prior to establishing a VPN connection. This will require some clever scripting and perhaps automation using a scheduled task based on an event trigger. I will leave that custom configuration as an exercise for the reader. If you’ve developed something to address this challenge, please feel free to share in the comments below. 🙂

Additional Information

Always On VPN Protocol Recommendations for Windows Server RRAS

Always On VPN IKEv2 Security Configuration

Always On VPN Certificate Requirements for IKEv2

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster Load Balancer

Troubleshooting Always On VPN Error Code 0x80092013

Troubleshooting Always On VPN Error Code 0x80092013Windows Server Routing and Remote Access Service (RRAS) is commonly used for Windows 10 Always On VPN deployments because it is easy to configure and manage and it includes Microsoft’s proprietary Secure Socket Tunneling Protocol (SSTP). SSTP is a Transport Layer Security (TLS) VPN protocol that is firewall-friendly and ubiquitously available. However, a common configuration mistake can lead to failed connections.

Error 0x80092013

A Windows 10 Always On VPN client may fail to establish a VPN connection to an RRAS VPN server when using SSTP. The VPN client will return the following error message.

“Can’t connect to Always On VPN. The revocation function was unable to check revocation because the revocation server was offline.”

Troubleshooting Always On VPN Error Code 0x80092013

The event log will also include RasClient event ID 20227 with the following error.

“The user [domain\user] dialed a connection named [connection name] which has failed. The error code returned on failure is -2146885613.”

Troubleshooting Always On VPN Error Code 0x80092013

The Win32 error code –2146885613 converts to hexadecimal 0x80092013, which translates to CRYPT_E_REVOCATION_OFFLINE, indicating that the client was unable to successfully perform a check of the VPN server’s SSL certificate.

Revocation Checking

When the VPN client attempts to establish an SSTP connection to the Windows RRAS VPN, it will check the Certification Revocation List (CRL) using the information provided in the SSL certificate. If the CRL is unreachable for any reason, the client will not complete the connection

Common Cause of Error 0x80092013

Certificate revocation failures for Windows 10 Always On VPN SSTP connections commonly occur when the RRAS VPN server is configured with an SSL certificate issued by an internal certification authority (CA) and the CRL is not publicly available.

Resolving Error 0x80092013

Making the internal CA’s CRL available publicly will of course resolve this error. However, best practice recommendations for the SSTP SSL certificate call for the use of a certificate issued by a public CA. For detailed information about SSL certificate requirements and recommendations, please see Always On VPN SSL Certificate Requirements for SSTP.

Additional Information

Always On VPN SSL Certificate Requirements for SSTP

Always On VPN ECDSA SSL Certificate Request for SSTP

Always On VPN Protocol Recommendations for Windows RRAS

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