Always On VPN Load Balancing for RRAS in Azure

Always On VPN Load Balancing for RRAS in AzurePreviously I wrote about Always On VPN options for Microsoft Azure deployments. In that post I indicated that running Windows Server with the Routing and Remote Access Service (RRAS) role for VPN was an option to be considered, even though it is not a formally supported workload. Despite the lack of support by Microsoft, deploying RRAS in Azure works well and is quite popular. In fact, I recently published some configuration guidance for RRAS in Azure.

Load Balancing Options for RRAS

Multiple RRAS servers can be deployed in Azure to provide failover/redundancy or to increase capacity. While Windows Network Load Balancing (NLB) can be used on-premises for RRAS load balancing, NLB is not supported and doesn’t work in Azure. With that, there are several options for load balancing RRAS in Azure. They include DNS round robin, Azure Traffic Manager, the native Azure load balancer, Azure Application Gateway, or a dedicated load balancing virtual appliance.

DNS Round Robin

The easiest way to provide load balancing for RRAS in Azure is to use round robin DNS. However, using this method has some serious limitations. Simple DNS round robin can lead to connection attempts to a server that is offline. In addition, this method doesn’t accurately balance the load and often results in uneven distribution of client connections.

Azure Traffic Manager

Using Azure Traffic Manager is another alternative for load balancing RRAS in Azure. In this scenario each VPN server will have its own public IP address and FQDN for which Azure Traffic Manager will intelligently distribute traffic. Details on configuring Azure Traffic Manager for Always On VPN can be found here.

Azure Load Balancer

The native Azure load balancer can be configured to provide load balancing for RRAS in Azure. However, it has some serious limitations. Consider the following.

  • Supports Secure Socket Tunneling Protocol (SSTP) only.
  • Basic health check functionality (port probe only).
  • Limited visibility.
  • Does not work with IKEv2.
  • Does not support TLS offload for SSTP.

More information about the Azure Load Balancer can be found here.

Azure Application Gateway

The Azure Application Gateway can be used for load balancing RRAS SSTP VPN connections where advanced capabilities such as enhanced health checks and TLS offload are required. More information about the Azure Application Gateway can be found here.

Load Balancing Appliance

Using a dedicated Application Delivery Controller (ADC), or load balancer is a very effective way to eliminate single points of failure for Always On VPN deployments hosted in Azure. ADCs provide many advanced features and capabilities to ensure full support for all RRAS VPN protocols. In addition, ADCs offer much better visibility and granular control over VPN connections. There are many solutions available as virtual appliances in the Azure marketplace that can be deployed to provide RRAS load balancing in Azure.

Summary

Deploying Windows Server RRAS in Azure for Always On VPN can be a cost-effective solution for many organizations. Although not a formally supported workload, I’ve deployed it numerous times and it works quite well. Consider using a dedicated ADC to increase scalability or provide failover and redundancy for RRAS in Azure whenever possible.

Additional Information

Windows 10 Always On VPN Options for Azure Deployments

Windows 10 Always On VPN and RRAS in Microsoft Azure

Windows 10 Always On VPN with Microsoft Azure Gateway

Error Importing Windows Server RRAS Configuration

Error Importing Windows Server RRAS Configuration Windows Server and the Routing and Remote Access Service (RRAS) is a popular choice for Windows 10 Always On VPN deployments. It is easy to implement and support, offers flexible scalability, and is cost-effective. In addition, it provides support for a TLS-based VPN protocol which is required for many deployments.

Configuration Backup

When deploying RRAS to support Always On VPN, it’s an excellent idea to export the configuration once all settings have been finalized. Often this is done by opening an elevated command window and running netsh.exe ras dump and piping the output to a text file, as shown here.

netsh.exe ras dump > rasconfig.txt

Import Error

Importing a saved configuration is accomplished by opening an elevated command window and running netsh.exe exec [filename], as shown here.

netsh.exe exec rasconfig.txt

Oddly, this doesn’t work by default. The import will fail and return the following error message.

“The following command was not found: ■.”

Error Importing Windows Server RRAS Configuration

Root Cause

Importing the RRAS configuration fails because the default configuration output is saved in Unicode format. Inexplicably this encoding is not recognized by netsh.exe when importing the configuration.

Workaround

Follow the steps below to save the configuration file in a format that can be imported using netsh.exe.

1. Open the exported configuration file using notepad.exe.
2. From the Menu bar choose File > Save As.
3. From the Encoding drop-down list choose ANSI.
4. Click Save.

Error Importing Windows Server RRAS Configuration

Once complete, import the file using netsh.exe exec [filename]. Restart the RemoteAccess service to apply the changes.

PowerShell

Administrators can use PowerShell to export the RRAS configuration and ensure the correct encoding format is used by default. To do this, open an elevated PowerShell window and run the following command.

Invoke-Command -ScriptBlock {netsh ras dump} | Out-File [filename] -Encoding ASCII

Additional Information

Windows 10 Always On VPN and Windows Server Routing and Remote Access Service (RRAS)

Windows 10 Always On VPN Protocol Recommendations for Windows Server Routing and Remote Access Service (RRAS)

Always On VPN SSTP Load Balancing with Kemp LoadMaster

Always On VPN SSTP Load Balancing with Kemp LoadMaster The Windows Server Routing and Remote Access Service (RRAS) includes support for the Secure Socket Tunneling Protocol (SSTP), which is a Microsoft proprietary VPN protocol that uses SSL/TLS for security and privacy of VPN connections. The advantages of using SSTP for Always On VPN is that it is firewall friendly and ensures consistent remove connectivity even behind highly restrictive firewalls.

Load Balancing SSTP

In a recent post, I described some of the use cases and benefits of SSTP load balancing as well as the offloading of TLS for SSTP VPN connections. Using a load balancer for SSTP VPN connections increases scalability, and offloading TLS for SSTP reduces resource utilization and improves performance for VPN connections. There are positive security benefits too.

Note: A comprehensive reference with detailed, prescriptive guidance for configuring the Kemp LoadMaster for Always On VPN can be found in the Always On VPN Load Balancing Deployment Guide for Kemp Load Balancers. Download this free guide now!

Configuration

Enabling load balancing on the Kemp LoadMaster platform is fundamentally similar to load balancing HTTPS web servers. However, there are a few subtle but important differences.

Health Check

Using a standard TCP port check on the LoadMaster will not accurately reflect the health of the SSTP service running on the RRAS server. In addition, using a simple TCP port check could yield unexpected results. To ensure accurate service status monitoring, it is recommended that HTTP or HTTPS health checks be configured instead.

Real Server Check Method

Open the Kemp LoadMaster management console and follow the steps below to enable HTTP/HTTPS health checks for SSTP.

1. Expand Virtual Services in the navigation pane.
2. Click View/Modify Services.
3. Click Modify on the SSTP VPN virtual service.
4. Expand Real Servers.
5. Select HTTPS Protocol from the Real Server Check Method drop-down list. Alternatively, if TLS offload is enabled select HTTP Protocol.
6. In the URL field enter /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ and click Set URL.
7. In the Status Codes field enter 401 and click Set Status Codes.
8. Check the box next to Use HTTP/1.1.
9. Select Head from the HTTP Method drop-down list.

Always On VPN SSTP Load Balancing with Kemp LoadMaster

TLS Offload

It is generally recommended that TLS offload not be enabled for SSTP VPN. However, if TLS offload is desired, it is configured in much the same way as a common HTTPS web server. Specific guidance for enabling TLS offload on the Kemp LoadMaster load balancer can be found in the Always On VPN Load Balancing Deployment Guide for Kemp Load Balancers. Details for configuring RRAS and SSTP to support TLS offload can be found here.

Certificates

When enabling TLS offload for SSTP VPN connections it is recommended that the public SSL certificate be installed on the RRAS server, even though TLS processing will be handled on the LoadMaster and HTTP will be used between the LoadMaster and the RRAS server. If installing the public SSL certificate on the RRAS server is not an option, additional configuration will be required. Specifically, TLS offload for SSTP must be configured using the Enable-SSTPOffload PowerShell script, which can be found here.

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

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

Example:

Enable-SSTPOffload -CertificateHash “C3AB8FF13720E8AD9047DD39466B3C8974E592C2FA383D4A3960714CAEF0C4F2” -Restart

Re-Encryption

When offloading TLS for SSTP VPN connections, all traffic between the LoadMaster and the RRAS server will be sent in the clear using HTTP. In some instances, TLS offload is required only for traffic inspection, not performance gain. In this scenario the LoadMaster will be configured to terminate and then re-encrypt connections to the RRAS server. When terminating TLS on the LoadMaster and re-encrypting connections to the RRAS server is required, the same certificate must be used on both the LoadMaster and the RRAS server. Using different certificates on the RRAS server and the load balancer is not supported.

Additional Information

Windows 10 Always On VPN Load Balancing Deployment Guide for Kemp Load Balancers

Windows 10 Always On VPN SSTP Load Balancing and SSL Offload

Windows 10 Always On VPN SSL Certificate Requirements for SSTP

Windows 10 Always On VPN ECDSA SSL Certificate Request for SSTP

Windows 10 Always On VPN SSTP Connects then Disconnects

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

Always On VPN SSTP Load Balancing with F5 BIG-IP

Always On VPN SSTP Load Balancing with F5 BIG-IP The Windows Server Routing and Remote Access Service (RRAS) includes support for the Secure Sockets Tunneling Protocol (SSTP), which is a Microsoft proprietary VPN protocol that uses SSL/TLS for security and privacy of VPN connections. The advantage of using SSTP for Always On VPN is that it is firewall friendly and ensures consistent remote connectivity even behind highly restrictive firewalls.

Load Balancing SSTP

In a recent post, I described some of the use cases and benefits of SSTP load balancing as well as the offloading of TLS for SSTP VPN connections. Using a load balancer for SSTP VPN connections increases scalability, and offloading TLS for SSTP reduces resource utilization and improves performance for VPN connections. There are positive security benefits too.

Configuration

Enabling load balancing for SSTP on the F5 BIG-IP platform is fundamentally similar to load balancing HTTPS web servers. However, there are a few subtle but important differences.

Default Monitor

The default HTTP and HTTPS monitors on the F5 will not accurately reflect the health of the SSTP service running on the RRAS server. In addition, using a simple TCP port monitor could yield unexpected results. To ensure accurate service status monitoring, a new custom monitor must be created to validate the health of the SSTP service.

Custom SSTP Monitor

Open the F5 BIG-IP management console and follow the steps below to create and assign a new custom monitor for SSTP.

Create Monitor

1. In the navigation tree highlight Local Traffic.
2. Click Monitors.
3. Click Create.

Always On VPN SSTP Load Balancing with F5 BIG-IP

4. Enter a descriptive name in the Name field and from the Type drop-down list choose HTTP if TLS offload is enabled, or HTTPS if it is not.
5. In the Send String field enter HEAD /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ HTTP/1.1\r\nHost:r\nConnection: Close\r\n\r\n.
6. In the Receive String field enter HTTP/1.1 401.
7. Click Finished.

Always On VPN SSTP Load Balancing with F5 BIG-IP

Assign Monitor

1. Below Local Traffic click Pools.
2. Click on the SSTP VPN server pool.
3. In the Health Monitors section select the SSTP VPN health monitor from the Available list and make it Active.
4. Click Update.

Always On VPN SSTP Load Balancing with F5 BIG-IP

CLI Configuration

If you prefer to configure the SSTP VPN monitor using the F5’s Command Line Interface (CLI), you can download the monitor configuration from my GitHub here.

TLS Offload

It is generally recommended that TLS offload not be enabled for SSTP VPN. However, if TLS offload is desired, it is configured in much the same way as a common HTTPS web server. Specific guidance for enabling TLS offload on the F5 BIG-IP can be found here. Details for configuring RRAS and SSTP to support TLS offload can be found here.

Certificates

When enabling TLS offload for SSTP VPN connections it is recommended that the public SSL certificate be installed on the RRAS server, even though TLS processing will be handled on the F5 and HTTP will be used between the F5 and the RRAS server. If installing the public SSL certificate on the RRAS server is not an option, additional configuration will be required. Specifically, TLS offload for SSTP must be configured using the Enable-SSTPOffload PowerShell script, which can be found here.

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

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

Example:

Enable-SSTPOffload -CertificateHash “C3AB8FF13720E8AD9047DD39466B3C8974E592C2FA383D4A3960714CAEF0C4F2” -Restart

Re-Encryption

When offloading TLS for SSTP VPN connections, all traffic between the F5 and the RRAS server will be sent in the clear using HTTP. In some instances, TLS offload is required only for traffic inspection, not performance gain. In this scenario the F5 will be configured to terminate and then re-encrypt connections to the RRAS server. When terminating TLS on the F5 and re-encrypting connections to the RRAS server is required, the same certificate must be used on both the F5 and the RRAS server. Using different certificates on the RRAS server and the load balancer is not supported.

Additional Information

Windows 10 Always On VPN SSTP Load Balancing and SSL Offload

Windows 10 Always On VPN SSL Certificate Requirements for SSTP

Windows 10 Always On VPN ECDSA SSL Certificate Request for SSTP

Windows 10 Always On VPN SSTP Connects then Disconnects

Windows 10 Always On VPN Load Balancing Deployment Guide for Kemp Load Balancers

 

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 SSTP Load Balancing with F5 BIG-IP

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.

Load Balancing Always On VPN SSTP Load Balancing with F5 BIG-IP

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 SSL Load Balancing with F5 BIG-IP

Windows 10 Always On VPN IKEv2 and SSTP Fallback

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

 

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

Always On VPN ECDSA SSL Certificate Request for SSTP

As I’ve discussed previously, it is strongly recommended that the TLS certificate used for SSTP be signed using the Elliptic Curve Digital Signature Algorithm (ECDSA). ECDSA provides better security and performance compared to RSA certificates for Windows 10 Always On VPN connections using SSTP. See my previous post Always On VPN SSL Certificate Requirements for SSTP for more information.

Certificate Signing Request

To generate a Certificate Signing Request (CSR) using ECDSA to send to a public Certification Authority (CA) using Windows, open the local computer certificate store (certlm.msc) on any Windows server or client and follow the steps below.

Note: Guidance for creating a CSR with ECDSA using OpenSSL can be found at the end of this post.

  1. Expand Certificates – Local Computer.
  2. Right-click the Personal folder and choose All Tasks > Advanced Operations > Create Custom Request.
  3. Click Next.
  4. Select Proceed without enrollment policy.
  5. Click Next.
  6. From the Template drop-down list choose (No template) CNG key.
  7. Click Next.
  8. Click Details.Always On VPN ECDSA SSL Certificate Request for SSTP
  9. Click Properties.
  10. On the General tab enter a name in the Friendly name field.
  11. Click on the Subject tab.
    1. In the Subject name section, from the Type drop-down list choose Common name.
    2. In the Value field enter the VPN server’s public hostname and click Add.
    3. In the Alternative name section, from the Type drop-down list choose DNS.
    4. In the Value field enter the VPN server’s public hostname and click Add.Always On VPN ECDSA SSL Certificate Request for SSTP
  12. Click on the Extensions tab.
    1. Expand Extended Key Usage (application policies).
    2. Highlight Server Authentication.
    3. Click Add.Always On VPN ECDSA SSL Certificate Request for SSTP
  13. Click on the Private Key tab.
    1. Expand Cryptographic Service Provider.
    2. Uncheck RSA,Microsoft Software Key Storage Provider.
    3. Check ECDSA_P256,Microsoft Software Key Storage Provider.Always On VPN ECDSA SSL Certificate Request for SSTP
  14. Expand Key options.
    1. Select the option to Make private key exportable.Always On VPN ECDSA SSL Certificate Request for SSTP
  15. Click Ok.
  16. Click Next.
  17. Enter a name for the file in the File Name field.
  18. Click Finish.

OpenSSL

If the TLS certificate for Always On VPN SSTP will be installed on a load balancer or other security device, creating the CSR using OpenSSL may be required. Use the following commands to generate a CSR with ECDA using OpenSSL.

openssl ecparam -out aovpn_sstp.key -name prime256v1 -genkey
openssl req -new -key aovpn_sstp.key -out aovpn_sstp.csr -sha256

Submit the Request

Once complete, submit the CSR for signing to your favorite public CA. Based on my experience, some CAs are easier to obtain ECDSA-signed certificates than other. Today, Digicert seems to be one of the better public CAs for obtaining EC TLS certificates.

Complete the Request

Once the CA has issued the certificate, import the certificate in to the local computer certificate store on the same client or server where the original CSR was created. The certificate can then be exported and imported on additional VPN servers, if required.

Additional Information

Always On VPN SSL Certificate Requirements for SSTP

Always On VPN Protocol Recommendations for RRAS

 

 

Always On VPN SSL Certificate Requirements for SSTP

Always On VPN Certificate Requirements for SSTPThe Windows Server 2016 Routing and Remote Access Service (RRAS) is commonly deployed as a VPN server for Windows 10 Always On VPN deployments. Using RRAS, Always On VPN administrators can take advantage of Microsoft’s proprietary Secure Socket Tunneling Protocol (SSTP) VPN protocol. SSTP is a Transport Layer Security (TLS) based VPN protocol that uses HTTPS over the standard TCP port 443 to encapsulate and encrypt communication between the Always On VPN client and the RRAS VPN server. SSTP is a firewall-friendly protocol that ensures ubiquitous remote network connectivity. Although IKEv2 is the protocol of choice when the highest level of security is required for VPN connections, SSTP can still provide very good security when implementation best practices are followed.

SSTP Certificate

Since SSTP uses HTTPS for transport, a common SSL certificate must be installed in the Local Computer/Personal/Certificates store on the RRAS VPN server. The certificate must include the Server Authentication Enhanced Key Usage (EKU) at a minimum. Often SSL certificates include both the Server Authentication and Client Authentication EKUs, but the Client Authentication EKU is not strictly required. The subject name on the certificate, or at least one of the Subject Alternative Name entries, must match the public hostname used by VPN clients to connect to the VPN server. Multi-SAN (sometimes referred to as UC certificates) and wildcard certificates are supported.

Always On VPN Certificate Requirements for SSTP

Certification Authority

It is recommended that the SSL certificate used for SSTP be issued by a public Certification Authority (CA). Public CAs typically have their Certificate Revocation Lists (CRLs) hosted on robust, highly available infrastructure. This reduces the chance of failed VPN connection attempts caused by the CRL being offline or unreachable.

Using an SSL certificate issued by an internal, private CA is supported if the CRL for the internal PKI is publicly available.

Key Type

RSA is the most common key type used for SSL certificates. However, Elliptic Curve Cryptography (ECC) keys offer better security and performance, so it is recommended that the SSTP SSL certificate be created using an ECC key instead.

Always On VPN Certificate Requirements for SSTP

To use an ECC key, be sure to specify the use of a Cryptographic Next Generation (CNG) key and select the ECDSA_P256 Microsoft Software Key Storage Provider (CSP) (or greater) when creating the Certificate Signing Request (CSR) for the SSTP SSL certificate.

Always On VPN Certificate Requirements for SSTP

Most public CAs will support certificate signing using ECC and Elliptic Curve Digital Signature Algorithm (ECDSA). If yours does not, find a better CA. 😉

Forward Secrecy

Forward secrecy (sometimes referred to as perfect forward secrecy, or PFS) ensures that session keys can’t be compromised even if the server’s private key is compromised. Using forward secrecy for SSTP is crucial to ensuring the highest levels of security for VPN connections.

To enforce the use of forward secrecy, the TLS configuration on the VPN server should be prioritized to prefer cipher suites with Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) key exchange.

Authenticated Encryption

Authenticated encryption (AE) and authenticated encryption with associated data (AEAD) is a form of encryption that provides better data protection and integrity compared to older block or stream ciphers such as CBC or RC4.

To enforce the use of authenticated encryption, the TLS configuration on the VPN server should be prioritized to prefer cipher suites that support Galois/Counter Mode (GCM) block ciphers.

Important Note: In Windows Server 2016, GCM ciphers can be used with both RSA and ECC certificates. However, in Windows Server 2012 R2 GCM ciphers can only be used when an ECC certificate is used.

SSL Offload

Offloading SSL to a load balancer or application delivery controller (ADC) can be enabled to improve scalability and performance for SSTP VPN connections. I will cover SSL offload for SSTP in detail in a future post.

Summary

SSTP can provide good security for VPN connections when implementation and security best practices are followed. For optimum security, use an SSL certificate with an EC key and optimize the TLS configuration to use forward secrecy and authenticated cipher suites.

Additional Information

Always On VPN ECDSA SSL Certificate Request for SSTP

Always On VPN and Windows Server Routing and Remote Access Service (RRAS)

Always On VPN Protocol Recommendations for Windows Server RRAS

Always On VPN Certificate Requirements for IKEv2

3 Important Advantages of Always On VPN over DirectAccess

Microsoft SSTP Specification on MSDN

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