Always On VPN LockDown Mode

Always On VPN LockDown ModeWhen an Always On VPN connection is provisioned to a Windows 10 client, there’s nothing to prevent a user from disconnecting or even deleting the connection. Some administrators have expressed concern about this, fearful that users may disable the VPN to improve performance or circumvent access controls when force tunneling is enabled. Also, administrators may wish to prevent users from accidentally or purposefully making changes to the configuration, or even deleting the connection entirely.

LockDown Mode

To address these concerns, Microsoft included a feature called LockDown mode for Always On VPN. Once enabled, the following conditions apply.

  • The LockDown VPN connection is always on.
  • The LockDown VPN connection cannot be disabled.
  • The user can’t make changes to or delete the LockDown connection.
  • No other VPN connections can exist on the client.
  • Force tunneling is enabled by default (split tunneling in LockDown mode is not supported).

Challenges with LockDown Mode

Always On VPN LockDown mode brings with it some unique challenges, however. Consider the following.

Limited Protocol Support

LockDown mode only supports IKEv2 and the native (built-in) VPN client. Third-party plug-in provider clients are not supported. IKEv2 is an excellent VPN protocol in terms of security, but operationally speaking it has some serious drawbacks.

Force Tunneling Only

LockDown mode uses force tunneling exclusively. All network traffic must go over the VPN connection. However, if the VPN connection is not available, the client will be unable to access any network resources at all, local or remote.

Captive Portal Issues

LockDown mode prevents clients from connecting to network resources from a network with a captive portal.

On-premises Connectivity

In LockDown mode all network traffic must flow over the VPN tunnel even if the client is on the internal network. This also means that if the VPN server is not reachable internally (unable to resolve public hostname, protocols/ports blocked by internal firewall, unable to route to VPN server, etc.) the client will not be able to access any internal or external network resources at all.

Deleting a LockDown VPN Connection

Deleting a LockDown VPN connection is also challenging. Administrators will find that trying to delete it using the UI or PowerShell often fails. To delete a LockDown Always On VPN connection, use psexec.exe to open an elevated PowerShell command window running in the system context using the following command.

.\psexec.exe -i -s C:\windows\system32\WindowsPowerShell\v1.0\powershell.exe

In the new elevated PowerShell window run the following commands to delete the LockDown VPN connection.

$Namespace = “root\cimv2\mdm\dmmap”
$ClassName = “MDM_VPNv2_01”

$obj = Get-CimInstance -Namespace $Namespace -ClassName $ClassName
Remove-CimInstance -CimInstance $obj

Optionally, download and run Remove-LockDownVPN.ps1 here.

Summary

While Always On VPN LockDown mode might seem like a good idea initially, its implementation is heavy-handed and practically speaking ends up causing more problems than it solves. For administrators that plan to enable this feature, carefully consider the drawbacks and limitations outlined above and their impact on supportability and the user experience.

Additional Information

Windows Always On VPN Device Tunnel Config using Microsoft Intune

Windows 10 Always On VPN Security Configuration 

Windows 10 Always On VPN Hands-On Training

 

Always On VPN Device Tunnel Configuration using Intune

Always On VPN Device Tunnel Configuration using IntuneA while back I described in detail how to configure a Windows 10 Always On VPN device tunnel connection using PowerShell. While using PowerShell is fine for local testing, it obviously doesn’t scale well. In theory you could deploy the PowerShell script and XML file using System Center Configuration Manager (SCCM), but using Microsoft Intune is the recommended and preferred deployment method. However, as of this writing Intune does not support device tunnel configuration natively. The administrator must create a ProfileXML manually and use Intune to deploy it.

Device Tunnel Prerequisites

I outlined the Always On VPN device tunnel prerequisites in my previous post here. To summarize, the client must be running Windows 10 Enterprise edition and be domain-joined. It must also have a certificate issued by the internal PKI with the Client Authentication EKU in the local computer certificate store.

ProfileXML

To begin, create a ProfileXML for the device tunnel that includes the required configuration settings and parameters for your deployment. You can find a sample Windows 10 Always On VPN device tunnel ProfileXML here.

Note: Be sure to define a custom IPsec policy in ProfileXML for the device tunnel. The default security settings for the IKEv2 protocol (required for the device tunnel) are quite poor. Details here.

Intune Deployment

Open the Intune management console and follow the steps below to deploy an Always On VPN device tunnel using Microsoft Intune.

Create Profile

1. Navigate to the Intune portal.
2. Click Device configuration.
3. Click Profiles.
4. Click Create profile.

Define Profile Settings

1. Enter a name for the VPN connection in the Name field.
2. Enter a description for the VPN connection in the Description field (optional).
3. Select Windows 10 and later from the Platform drop-down list.
4. Select Custom from the Profile type drop-down list.

Always On VPN Device Tunnel Configuration using Intune

Define Custom OMA-URI Settings

1. On the Custom OMA-URI Settings blade click Add.
2. Enter a name for the device tunnel in the Name field.
3. Enter a description for the VPN connection in the Description field (optional).
4. Enter the URI for the device tunnel in the OMA-URI field using the following syntax. If the profile name includes spaces they must be escaped, as shown here.

./Device/Vendor/MSFT/VPNv2/Example%20Profile%Name/ProfileXML

5. Select String (XML file) from the Data Type drop-down list.
6. Click the folder next to the Select a file field and chose the ProfileXML file created previously.
7. Click Ok twice and then click Create.

Always On VPN Device Tunnel Configuration using Intune

Assign Profile

Follow the steps below to assign the Always On VPN device tunnel profile to the appropriate device group.

1. Click Assignments.
2. Click Select groups to include.
3. Select the group that includes the Windows 10 client devices.
4. Click Select.
5. Click Save.

Always On VPN Device Tunnel Configuration using Intune

Demonstration Video

A video demonstration of the steps outlined above can be viewed here.

Additional Information

Windows 10 Always On VPN Device Tunnel Configuration using PowerShell

Windows 10 Always On VPN IKEv2 Security Configuration

Deleting a Windows 10 Always On VPN Device Tunnel

Windows 10 Always On VPN Device Tunnel Missing in the UI

Video: Deploying Windows 10 Always On VPN User Tunnel with Microsoft Intune

Always On VPN Training in Switzerland June 2019

Always On VPN Training in Switzerland June 2019I’m pleased to announce that I’ll be bringing my popular Windows 10 Always On VPN hands-on training course to Europe in June this year! Many of you asked about training opportunities outside of the U.S., so I’ve added a class to be held in Bern, Switzerland from June 3-5, 2019.

Sponsored by RealStuff, this three-day hands-on training class will provide comprehensive education covering all aspects of an Always On VPN deployment, including the following.

  • Windows 10 Always On VPN overview
  • Introduction to CSP
  • Infrastructure requirements
  • Planning and design considerations
  • Installation, configuration, and client provisioning

Additional advanced topics will also be covered.

  • Redundancy and high availability
  • Cloud-based deployments
  • Third-party VPN infrastructure and client support
  • Multifactor authentication
  • Always On VPN migration strategies

Windows 10 Always On VPN Hands-On Training Classes for 2018

Don’t miss out on this valuable learning opportunity! Seating is limited, so register today!

Always On VPN Training in Switzerland June 2019

Always On VPN Device Tunnel Does Not Connect Automatically

When configuring a Windows 10 Always On VPN device tunnel, the administrator may encounter a scenario in which the device tunnel does not connect automatically. This can occur even when ProfileXML is configured with the AlwaysOn element set to “true”.

Always On VPN Device Tunnel Does Not Connect Automatically

Manual Connection

An administrator can establish a device tunnel connection manually using rasdial.exe however, indicating no issues with connectivity or authentication that would prevent a successful automatic connection.

Always On VPN Device Tunnel Does Not Connect Automatically

Root Cause

This scenario will occur when the device tunnel configuration is applied to a Windows 10 Professional edition client.

Always On VPN Device Tunnel Does Not Connect Automatically

Device Tunnel Support

The Windows 10 Always On VPN device tunnel is supported only on Windows 10 1709 or later Enterprise edition clients that are domain-joined. To ensure the device tunnel connects automatically, upgrade to Windows 10 Enterprise 1709 or later and join it to a domain.

Always On VPN Device Tunnel Does Not Connect Automatically

Source: https://docs.microsoft.com/en-us/windows-server/remote/remote-access/vpn/vpn-device-tunnel-config#device-tunnel-requirements-and-features

Additional Information

Windows 10 Always On VPN Device Tunnel Configuration using PowerShell

Windows 10 Always On VPN Device Tunnel Missing in the Windows UI

Deleting a Windows 10 Always On VPN Device Tunnel

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Always On VPN IKEv2 Load Balancing with F5 BIG-IPThe Internet Key Exchange version 2 (IKEv2) is the protocol of choice for Always On VPN deployments where the highest level of security is required. Implementing Always On VPN at scale often requires multiple VPN servers to provide sufficient capacity and to provide redundancy. Commonly an Application Delivery Controller (ADC) or load balancer is configured in front of the VPN servers to provide scalability and high availability for Always On VPN.

Load Balancing IKEv2

In a recent post I described some of the unique challenges load balancing IKEv2 poses, and I demonstrated how to configure the Kemp LoadMaster load balancer to properly load balance IKEv2 VPN connections. In this post I’ll outline how to configure IKEv2 VPN load balancing on the F5 BIG-IP load balancer.

Note: This article assumes the administrator is familiar with basic F5 BIG-IP load balancer configuration, such as creating nodes, pools, virtual servers, etc.

Initial Configuration

Follow the steps below to create a virtual server on the F5 BIG-IP to load balance IKEv2 VPN connections.

Pool Configuration

To begin, create two pools on the load balancer. The first pool will be configured to use UDP port 500, and the second pool will be configured to use UDP port 4500. Each pool is configured with the VPN servers defined as the individual nodes.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Virtual Server Configuration

Next create two virtual servers, the first configured to use UDP port 500 and the second to use UDP port 4500.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Persistence Profile

To ensure that both IKEv2 UDP 500 and 4500 packets are delivered to the same node, follow the steps below to create and assign a Persistence Profile.

1. Expand Local Traffic > Profiles and click Persistence.
2. Click Create.
3. Enter a descriptive name for the profile in the Name field.
4. Select Source Address Affinity from the Persistence Type drop-down list.
5. Click the Custom check box.
6. Select the option to Match Across Services.
7. Click Finished.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Assign the new persistence profile to both UDP 500 and 4500 virtual servers. Navigate to the Resources tab on each virtual server and select the new persistence profile from the Default Persistence Profile drop-down list. Be sure to do this for both virtual servers.

Always On VPN IKEv2 Load Balancing with F5 BIG-IP

Additional Resources

Windows 10 Always On VPN IKEv2 Load Balancing with Kemp LoadMaster Load Balancer 

Windows 10 Always On VPN IKEv2 Security Configuration

Windows 10 Always On VPN and IKEv2 Fragmentation

Windows 10 Always On VPN Certificate Requirements for IKEv2

Video: Windows 10 Always On VPN Load Balancing with the Kemp LoadMaster Load Balancer

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

 

Troubleshooting Always On VPN Error Code 809

When testing an Always On VPN connection, the administrator may encounter a scenario where the VPN client fails to connect to the VPN server. On the Windows 10 client the error message states the following.

“Can’t connect to [connection name]. The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g. firewalls, NAT, routers, etc.) between your computer and the remote server is not configured to allow VPN connections. Please contact your Administrator or your service provider to determine which device may be causing the problem.”

Always On VPN and IKEv2 Fragmentation

In addition, the Application event log records an error message with Event ID 20227 from the RasClient source. The error message states the following.

“The User [username] dialed a connection named [connection name] with has failed. The error code returned on failure is 809.”

Troubleshooting Always On VPN Error Code 809

Connection Timeout

The error code 809 indicates a VPN timeout, meaning the VPN server failed to respond. Often this is related directly to network connectivity, but sometimes other factors can come in to play.

Troubleshooting VPN Error Code 809

When troubleshooting VPN error code 809 the following items should be carefully checked.

  • Name Resolution – Ensure the VPN server’s public hostname resolves to the correct IP address.
  • Firewall Configuration – Confirm the edge firewall is configured properly. Inbound TCP port 443 is required for the Secure Socket Tunneling Protocol (SSTP) and inbound UDP ports 500 and 4500 are required for the Internet Key Exchange version 2 (IKEv2) protocol. Make sure that any NAT rules are forwarding traffic to the correct server.
  • Load Balancer Configuration – If VPN servers are located behind a load balancer, make certain that virtual IP address and ports are configured correctly and that health checks are passing. For IKEv2 specifically, it is crucial that UDP ports 500 and 4500 be delivered to the same backend server. This commonly requires custom configuration. For example, on the KEMP LoadMaster the administrator will configure “port following”. On the F5 BIG-IP a  custom “persistence profile” must be configured. On the Citrix NetScaler a “persistency group” must be defined.

IKEv2 Fragmentation

VPN error code 809 can also be caused by IKE fragmentation when using the IKEv2 VPN protocol. During IKEv2 connection establishment, payload sizes may exceed the IP Maximum Transmission Unit (MTU) for the network path between the client and server. This causes the IP packets to be fragmented. However, it is not uncommon for intermediary devices (routers, NAT devices, or firewalls) to block IP fragments. When this occurs, a VPN connection cannot be established. However, looking at a network trace of the connection attempt, the administrator will see that the connection begins but subsequently fails.

Troubleshooting Always On VPN Error Code 809

Enable IKEv2 Fragmentation Support

The IKEv2 protocol includes support for fragmenting packets at the IKE layer. This eliminates the need for fragmenting packets at the IP layer. IKEv2 fragmentation must be configured on both the client and server.

Client

IKEv2 fragmentation was introduced in Windows 10 1803 and is enabled by default. No client-side configuration is required.

Server

IKEv2 is commonly supported on many firewall and VPN devices. Consult the vendor’s documentation for configuration guidance. For Windows Server Routing and Remote Access (RRAS) servers, IKEv2 fragmentation was introduced in Windows Server 1803 and is also supported in Windows Server 2019. It is enabled via a registry key. The following PowerShell command can be used to enable IKEv2 fragmentation on supported servers.

New-ItemProperty -Path “HKLM:\SYSTEM\CurrentControlSet\Services\RemoteAccess\Parameters\Ikev2\” -Name EnableServerFragmentation -PropertyType DWORD -Value 1 -Force

Validation

Once IKEv2 fragmentation is configured on the VPN server, a network capture will reveal the IKE_SA_INIT packet now includes the IKEV2_FRAGMENTATION_SUPPORTED notification message.

Always On VPN and IKEv2 Fragmentation

Additional Information

Windows 10 Always On VPN and IKEv2 Fragmentation

Windows 10 Always On VPN IKEv2 Security Configuration

Windows 10 Always On VPN Hands-On Training Classes

Always On VPN and IKEv2 Fragmentation

The IKEv2 protocol is a popular choice when designing an Always On VPN solution. When configured correctly it provides the best security compared to other protocols. The protocol is not without some unique challenges, however. IKEv2 is often blocked by firewalls, which can prevent connectivity. Another lesser know issue with IKEv2 is that of fragmentation. This can result in failed connectivity that can be difficult to troubleshoot.

IP Fragmentation

IKEv2 uses UDP for transport, and typically most packets are relatively small. The exception to this is when authentication takes place, especially when using client certificate authentication. The problem is further complicated by long certificate chains and by RSA keys, especially those that are greater than 2048 bit. If the payload exceeds 1500 bytes, the IP packet will have to be broken in to smaller fragments to be sent over the network. If an intermediary device in the path is configured to use a smaller Maximum Transmission Unit (MTU), that device may fragment the IP packets.

IP Fragmentation and Firewalls

Many routers and firewalls are configured to drop IP fragments by default. When this happens, IKEv2 communication may begin initially, but subsequently fail. This typically results in an error code 809 with a message stating the following.

“Can’t connect to [connection name]. The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g. firewalls, NAT, routers, etc.) between your computer and the remote server is not configured to allow VPN connections. Please contact your Administrator or your service provider to determine which device may be causing the problem.”

Always On VPN and IKEv2 Fragmentation

Troubleshooting

When troubleshooting potential IKEv2 fragmentation-related connection failures, a network trace should be taken of the connection attempt on the client. Observe the packet sizes during the conversation, especially IKE_AUTH packets. Packet sizes exceeding the path MTU will have to be fragmented, as shown here.

Always On VPN and IKEv2 Fragmentation

Measuring Path MTU

Measuring the path MTU between the client and server can be helpful when troubleshooting fragmentation related issues. The mtupath.exe utility is an excellent and easy to use tool for this task. The tool can be downloaded here.

Always On VPN and IKEv2 Fragmentation

IKEv2 Fragmentation

To address the challenges with IP fragmentation and potential connectivity issues associated with network devices dropping fragmented packets, the IKEv2 protocol itself can be configured to perform fragmentation at the IKE layer. This eliminates the need for IP layer fragmentation, resulting in better reliability for IKEv2 VPN connections.

Both the server and the client must support IKEv2 fragmentation for this to occur. Many firewall and VPN vendors include support for IKEv2 fragmentation. Consult the vendor’s documentation for configuration guidance. For Windows Server Routing and Remote Access (RRAS) servers, the feature was first introduced in Windows Server 1803 and is supported in Windows Server 2019. Windows 10 clients support IKEv2 fragmentation beginning with Windows 10 1803.

Enabling IKEv2 Fragmentation

Windows 10 clients support IKEv2 fragmentation by default. However, it must be enabled on the server via the registry. The following PowerShell command will enable IKEv2 fragmentation support on Windows Server 1803 and later.

New-ItemProperty -Path “HKLM:\SYSTEM\CurrentControlSet\Services\RemoteAccess\Parameters\Ikev2\” -Name EnableServerFragmentation -PropertyType DWORD -Value 1 -Force

Validation Testing

Once IKEv2 fragmentation is configured on the VPN server, a network capture will reveal the IKE_SA_INIT packet now includes the IKEV2_FRAGMENTATION_SUPPORTED notification message.

Always On VPN and IKEv2 Fragmentation

Additional Information

Windows 10 Always On VPN IKEv2 Security Configuration

RFC 7383 – IKEv2 Message Fragmentation

IEA Software MTU Path Scan Utility

Windows 10 Always On VPN Hands-On Training Classes

Always On VPN and Network Policy Server (NPS) Load Balancing

Always On VPN and Network Policy Server (NPS) Load BalancingLoad balancing Windows Server Network Policy Servers (NPS) is straightforward in most deployment scenarios. Most VPN servers, including Windows Server Routing and Remote Access Service (RRAS) servers allow the administrator to configure multiple NPS servers for redundancy and scalability. In addition, most solutions support weighted distribution, allowing administrators to distribute requests evenly between multiple NPS servers (round robin load balancing) or to distribute them in order of priority (active/passive failover).

The Case for NPS Load Balancing

Placing NPS servers behind a dedicated network load balancing appliance is not typically required. However, there are some deployment scenarios where doing so can provide important advantages.

Deployment Flexibility

Having NPS servers fronted by a network load balancer allows the administrator to configure a single, virtual IP address and hostname for the NPS service. This provides deployment flexibility by allowing administrators to add or remove NPS servers without having to reconfigure VPN servers, network firewalls, or VPN clients. This can be beneficial when deploying Windows updates, migrating NPS servers to different subnets, adding more NPS servers to increase capacity, or performing rolling upgrades of NPS servers.

Traffic Shaping

Dedicated network load balancers allow for more granular control and of NPS traffic. For example, NPS routing decisions can be based on real server availability, ensuring that authentication requests are never sent to an NPS server that is offline or unavailable for any reason. In addition, NPS traffic can be distributed based on server load, ensuring the most efficient use of NPS resources. Finally, most load balancers also support fixed or weighted distribution, enabling active/passive failover scenarios if required.

Traffic Visibility

Using a network load balancer for NPS also provides better visibility for NPS authentication traffic. Most load balancers feature robust graphical displays of network utilization for the virtual server/service as well as backend servers. This information can be used to ensure enough capacity is provided and to monitor and plan for additional resources when network traffic increases.

Configuration

Before placing NPS servers behind a network load balancer, the NPS server certificate must be specially prepared to support this unique deployment scenario. Specifically, the NPS server certificate must be configured with the Subject name of the cluster, and the Subject Alternative Name field must include both the cluster name and the individual server’s hostname.

Always On VPN and Network Policy Server (NPS) Load Balancing

Always On VPN and Network Policy Server (NPS) Load Balancing

Create Certificate Template

Perform the following steps to create a certificate template in AD CS to support NPS load balancing.

  1. Open the Certificate Templates management console (certtmpl.msc) on the certification authority (CA) server or a management workstation with remote administration tool installed.
  2. Right-click the RAS and IAS Servers default certificate template and choose Duplicate.
  3. Select the Compatibility tab.
    1. Select Windows Server 2008 or a later version from the Certification Authority drop-down list.
    2. Select Windows Vista/Server 2008 or a later version from the Certificate recipient drop-down list.
  4. Select the General tab.
    1. Enter a descriptive name in the Template display name field.
    2. Choose an appropriate Validity period and Renewal period.
    3. Do NOT select the option to Publish certificate in Active Directory.
  5. Select the Cryptography tab.
    1. Chose Key Storage Provider from the Provider Category drop-down list.
    2. Enter 2048 in the Minimum key size field.
    3. Select SHA256 from the Request hash drop-down list.
  6. Select the Subject Name tab.
    1. Select the option to Supply in the request.
  7. Select the Security tab.
    1. Highlight RAS and IAS Servers and click Remove.
    2. Click Add.
    3. Enter the security group name containing all NPS servers.
    4. Check the Read and Enroll boxes in the Allow column in the Permissions for [group name] field.
  8. Click Ok.

Perform the steps below to publish the new certificate template in AD CS.

  1. Open the Certification Authority management console (certsrv.msc) on the certification authority (CA) server or a management workstation with remote administration tool installed.
  2. Expand Certification Authority (hostname).
  3. Right-click Certificate Templates and choose New and Certificate Template to Issue.
  4. Select the certificate template created previously.
  5. Click Ok.

Request Certificate on NPS Server

Perform the following steps to request a certificate for the NPS server.

  1. Open the Certificates management console (certlm.msc) on the NPS server.
  2. Expand the Personal folder.
  3. Right-click Certificates and choose All Tasks and Request New Certificate.
  4. Click Next.
  5. Click Next.
  6. Select the NPS server certificate template and click More information is required to enroll for this certificate link.
  7. Select the Subject tab.
    1.  Select Common name from the Type drop-down list in the Subject name section.
    2. Enter the cluster fully-qualified hostname (FQDN) in the Value field.
    3. Click Add.
    4. Select DNS from the Type drop-down list in the Alternative name section.
    5. Enter the cluster FQDN in the Value field.
    6. Click Add.
    7. Enter the NPS server’s FQDN in the Value field.
    8. Click Add.
      Always On VPN and Network Policy Server (NPS) Load Balancing
  8. Select the General tab.
    1. Enter a descriptive name in the Friendly name field.
  9. Click Ok.
  10. Click Enroll.

Load Balancer Configuration

Configure the load balancer to load balance UDP ports 1812 (authentication) and 1813 (accounting). Optionally, to ensure that authentication and accounting requests go to the same NPS server, enable source IP persistence according to the vendor’s guidance. For the KEMP LoadMaster load balancer, the feature is called “port following”. On the F5 BIG-IP it is called a “persistence profile”, and on the Citrix NetScaler it is called a “persistency group”.

Additional Information

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Always On VPN Hands-On Training Classes in U.S. and Europe

%d bloggers like this: