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

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 ProfileXML Editing and Formatting with Visual Studio Code

Always On VPN ProfileXML Editing and Formatting with Visual Studio CodeWindows 10 Always On VPN is designed to be implemented and managed using a Mobile Device Management (MDM) platform such as Microsoft Intune. With Intune specifically, there is an option to configure an Always On VPN profile in the UI. However, it provides only limited support and does not include all settings and options required for many deployments. Crucially, IKEv2 advanced security settings cannot be configured using the Intune portal. Also, there is currently no option for configuring a device tunnel with Intune. In these scenarios the administrator must manually create a ProfileXML file and provision it using Intune, System Center Configuration Manager (SCCM), or PowerShell.

ProfileXML

ProfileXML includes all settings that define the Always On VPN connection. The options and settings available are documented in the VPNv2 Configuration Service Provider (CSP) reference on Microsoft’s web site. ProfileXML is formatted using elements and settings within those elements. The formatting and syntax are critical to ensuring proper operation. Any error in syntax or formatting can result in an error, such as those described here.

XML Readability

Formatting is also important for readability, which is often helpful when reviewing configuration settings or troubleshooting syntax errors. For example, an element may be defined correctly but may be nested wrong. Often XML files are created with all text being left-justified, or with everything on a single line, making the content difficult to read. Using a file editor that recognizes XML files can be beneficial.

Visual Studio Code

To create, edit, and review ProfileXML it is recommended that a proper editing tool be used. I recommend using Microsoft’s Visual Studio Code. It is free, and it is especially helpful when editing XML files. Visual Studio Code can be downloaded here.

XML Tools VS Code Plug-In

To further enhance Visual Studio Code’s XML editing and formatting capabilities I recommend installing the XML Tools plug-in. This tool extends the native features of VS code for handling XML files. One important thing it adds is a formatting feature that will make your ProfileXML much easier to manage. The XML Tools plug-in for VS Code can be downloaded here.

XML Formatting

Once the XML Tools plug-in for VS code has been installed, formatting XML for readability is straightforward. Simply right-click anywhere in the document and choose Format Document.

Always On VPN ProfileXML Editing and Formatting with Visual Studio CodeOnce complete, the XML document will be formatted with proper indenting and nesting of elements, as shown here.

Always On VPN ProfileXML Editing and Formatting with Visual Studio CodeSummary

Formatting and syntax must be strictly adhered to when creating a ProfileXML file for Windows 10 Always On VPN. Using Visual Studio Code with the XML Tools plug-in allow the administrator to create and edit XML with proper formatting, which greatly improves readability and allows for streamlined configuration review and troubleshooting.

Acknowledgements

Special thanks to Colin, an avid reader of the articles on this web site for this tip. Thanks, Colin! 🙂

Additional Information

Always On VPN and DirectAccess Scripts and Sample Files on GitHub

Always On VPN IKEv2 Security Configuration

Always On VPN Device Tunnel Step-by-Step Configuration using PowerShell

Always On VPN Hands-On Training Classes in 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 IKEv2 Connection Failure Error Code 800

Always On VPN administrators may encounter a scenario in which Windows 10 clients are unable to establish an IKEv2 VPN connection to a Windows Server Routing and Remote Access Service (RRAS) server or a third-party VPN device under the following conditions.

  1. The VPN connection is configured using ProfileXML.
  2. ProfileXML includes the <CryptographySuite> element.
  3. The VPN server is configured to use a custom IPsec policy.
  4. The VPN server supports only IKEv2.
  5. The <NativeProtocolType> in ProfileXML is set to Automatic.

When these specific conditions are met, the client will be unable to connect to the VPN server using IKEv2. The error message states:

The remote connection was not made because the attempted VPN tunnels failed. The VPN server might be unreachable. If this connection is attempting to use an L2TP/IPsec tunnel, the security parameters required for IPsec negotiation might not be configured properly.

Always On VPN IKEv2 VPN Connection Failure Error Code 800

In addition, the event log will include an error message from the RasClient source with event ID 20227 that includes the following error message.

The user [username] dialed a connection named [connection name] which has failed. The error code returned on failure is 800.

Always On VPN IKEv2 VPN Connection Failure Error Code 800

A manually configured VPN connection using IKEv2 will connect successfully under these same conditions, however.

IKEv2 Error Code 800

Error code 800 translates to ERROR_AUTOMATIC_VPN_FAILED, which is somewhat ambiguous. The error description is:

Unable to establish the VPN connection. The VPN server may be unreachable, or security parameters may not be configured properly for this connection.

Digging Deeper

A network trace of the IKEv2 VPN connection reveals the true source of the problem, which is a failure of the client and server to successfully negotiate an IKEv2 security association (SA). During the SA initiation process, the parameters offered by the client are unacceptable to the server, resulting in a NO_PROPOSAL_CHOSEN notification being returned by the server.

Always On VPN IKEv2 VPN Connection Failure Error Code 800

Custom Cryptography Settings Ignored

It appears that the Always On VPN connection ignores the custom cryptography settings defined in the CryptographySuite element in ProfileXML. However, this only occurs when the NativeProtocolType is set to Automatic. Presumably, this is a bug. 🙂

Workaround

As a workaround, set the NativeProtocolType to IKEv2. When NativeProtocolType is set to IKEv2, the VPN connection recognizes the IKEv2 parameters defined in the CryptographySuite element and the VPN connection will be established successfully.

Additional Information

Always On VPN IKEv2 Security Configuration

Always On VPN Certificate Requirements for IKEv2

Always On VPN IKEv2 Load Balancing with the KEMP LoadMaster Load Balancer

Always On VPN IKEv2 Security Configuration

Always On VPN IKEv2 Security ConfigurationWhen deploying Windows 10 Always On VPN, many administrators choose the Internet Key Exchange version 2 (IKEv2) protocol to provide the highest level of security and protection for remote connections. However, many do not realize the default security parameters for IKEv2 negotiated between a Windows Server running the Routing and Remote Access Service (RRAS) and a Windows 10 VPN client are far less than ideal from a security perspective. Additional configuration on both the server and the client will be required to ensure adequate security and protection for IKEv2 VPN connections.

Windows 10 and RRAS IKEv2 Defaults

In their default configuration, a Windows 10 client connecting to a Windows Server running RRAS will negotiate an IKEv2 VPN connection using the following IPsec security parameters.

  • Encryption: 3DES
  • Authentication/Integrity: SHA-1
  • Key Size: DH Group 2 (1024 bit)

This information can be obtained by opening an elevated PowerShell command window and running the following command.

Get-NetIPsecMainModeSA | Select-Object -First 1

Always On VPN IKEv2 Security Configuration

This can also be confirmed by viewing a network trace as shown here.

Always On VPN IKEv2 Security Configuration

These IPsec security parameters might have been acceptable in the 90’s, but they certainly are not today. 🙂

Improving IKEv2 Security

To provide a baseline level of protection to meet today’s requirements for security and privacy for IKEv2 VPN connections, the following are the minimum recommended IPsec security parameters.

  • Encryption: AES128
  • Authentication/Integrity: SHA-256
  • Key Size: DH Group 14 (2048 bit)

RRAS Custom IPsec Policy

To implement these recommended security baselines for IKEv2 on a Windows Server running RRAS it will be necessary to define a custom IPsec security policy. To do this, open an elevated PowerShell command window and run the following commands on each RRAS server.

Set-VpnServerConfiguration -CustomPolicy -AuthenticationTransformConstants SHA256128 -CipherTransformConstants AES128 -DHGroup Group14 -EncryptionMethod AES128 -IntegrityCheckMethod SHA256 -PFSgroup PFS2048 -SADataSizeForRenegotiationKilobytes 102400

Restart the Remote Access Management service for the changes to take effect.

Restart-Service RaMgmtSvc -PassThru

Always On VPN IKEv2 Security Configuration

Windows 10 Client Settings

The IPsec policy must match on both the server and the client for an IKEv2 VPN connection to be successful. Unfortunately, none of the IKEv2 IPsec security association parameters proposed by default on Windows 10 clients use 2048-bit keys (DH Group 14), so it will be necessary to define a custom IPsec security policy on the client to match the settings configured on the server.

To configure a matching IPsec security policy on an individual Windows 10 VPN client, open an elevated PowerShell command window and run the following command.

$connection = “[connection name]”
Set-VpnConnectionIPsecConfiguration -ConnectionName $connection -AuthenticationTransformConstants SHA256128 -CipherTransformConstants AES128 -DHGroup Group14 -EncryptionMethod AES128 -IntegrityCheckMethod SHA256 -PFSgroup PFS2048 -Force

Always On VPN IKEv2 Security Configuration

Restore Defaults

In the process of testing it may be necessary to restore the default IKEv2 configuration on both the client and the server. This can be accomplished by running the following PowerShell commands.

Server – Set-VpnServerConfiguration -RevertToDefault

Client – Set-VpnConnectionIPsecConfiguration -ConnectionName [connection_name] -RevertToDefault -Force

Always On VPN XML Settings

To implement a custom IPsec policy using the minimum recommended security settings for an Always On VPN connection using IKEv2, add the following settings to your ProfileXML.

<VPNProfile>
 <NativeProfile>
  <CryptographySuite>
   <AuthenticationTransformConstants>SHA256128</AuthenticationTransformConstants>
   <CipherTransformConstants>AES128</CipherTransformConstants>
   <EncryptionMethod>AES128</EncryptionMethod>
   <IntegrityCheckMethod>SHA256</IntegrityCheckMethod>
   <DHGroup>Group14</DHGroup>
   <PfsGroup>PFS2048</PfsGroup>
  </CryptographySuite>
 </NativeProfile>
</VPNProfile>

Why Not AES 256?

In the examples above you’ll notice that I’ve chosen to use AES128 and not AES256. This is by design, as AES256 does not provide any practical additional security in most use cases. Details here.

Enhanced Security and Performance

To further improve security and performance for IKEv2, consider implementing Elliptic Curve Cryptography (EC) certificates and using Galois Counter Mode (GCM) cipher suites such as GCMAES128 for authentication and encryption.

Additional Information

Always On VPN Certificate Requirements for IKEv2

Always On VPN IKEv2 Connection Failure Error Code 800

Always On VPN IKEv2 Load Balancing with the KEMP LoadMaster Load Balancer

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Always On VPN IKEv2 Load Balancing with KEMP LoadMasterIKEv2 is an IPsec-based VPN protocol with configurable security parameters that allows administrators to ensure the highest level of security for Windows 10 Always On VPN clients. It is the protocol of choice for deployments that require the best possible protection for communication between remote clients and the VPN server. IKEv2 has some unique requirements when it comes to load balancing, however. Because it uses UDP on multiple ports, configuring the load balancer requires some additional steps for proper operation. This article demonstrates how to enable IKEv2 load balancing using the KEMP LoadMaster load balancer.

IKEv2 and NAT

IKEv2 VPN security associations (SAs) begin with a connection to the VPN server that uses UDP port 500. During this initial exchange, if it is determined that the client, server, or both are behind a device performing Network Address Translation (NAT), the connection switches to UDP port 4500 and the connection establishment process continues.

IKEv2 Load Balancing Challenges

Since UDP is connectionless, there’s no guarantee that when the conversation switches from UDP 500 to UDP 4500 that the load balancer will forward the request to the same VPN server on the back end. If the load balancer forwards the UDP 500 session from a VPN client to one real server, then forwards the UDP 4500 session to a different VPN server, the connection will fail. The load balancer must be configured to ensure that both UDP 500 and 4500 from the same VPN client are always forwarded to the same real server to ensure proper operation.

Port Following

To meet this unique requirement for IKEv2 load balancing, it is necessary to use a feature on the KEMP LoadMaster load balancer called “port following”. Enabling this feature will ensure that a VPN client using IKEv2 will always have their UDP 500 and 4500 sessions forwarded to the same real server.

Load Balancing IKEv2

Open the web-based management console and perform the following steps to enable load balancing of IKEv2 traffic on the KEMP LoadMaster load balancer.

Create the Virtual Server

  1. Expand Virtual Services.
  2. Click Add New.
  3. Enter the IP address to be used by the virtual server in the Virtual Address field.
  4. Enter 500 in the Port field.
  5. Select UDP from the Protocol drop-down list.
  6. Click Add this Virtual Service.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Add Real Servers

  1. Expand Real Servers.
  2. Click Add New.
  3. Enter the IP address of the VPN server in the Real Server Address field.
  4. Click Add This Real Server.
  5. Repeat the steps above for each VPN server in the cluster.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Repeat all the steps above to create another virtual server using UDP port 4500.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Enable Layer 7 Operation

  1. Click View/Modify Services below Virtual Services in the navigation tree.
  2. Select the first virtual server and click Modify.
  3. Expand Standard Options.
  4. Uncheck Force L4.
  5. Select Source IP Address from the Persistence Options drop-down list.
  6. Choose an appropriate value from the Timeout drop-down list.
  7. Choose an appropriate setting from the Scheduling Method drop-down list.
  8. Click Back.
  9. Repeat these steps on the second virtual server.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Enable Port Following

  1. Click View/Modify Services below Virtual Services in the navigation tree.
  2. Select the first virtual server and click Modify.
  3. Expand Advanced Properties.
  4. Select the virtual server using UDP 500 from the Port Following drop-down list.
  5. Click Back.
  6. Repeat these steps on the second virtual server.

Always On VPN IKEv2 Load Balancing with KEMP LoadMaster

Demonstration Video

The following video demonstrates how to enable IKEv2 load balancing for Windows 10 Always On VPN using the KEMP LoadMaster Load Balancer.

Summary

With the KEMP LoadMaster load balancer configured to use port following, Windows 10 Always On VPN clients using IKEv2 will be assured that their connections will always be delivered to the same back end VPN server, resulting in reliable load balancing for IKEv2 connections.

Additional Information

Windows 10 Always On VPN Certificate Requirements for IKEv2

Windows 10 Always On VPN Protocol Recommendations for Windows Server 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

Deploying Windows 10 Always On VPN with Microsoft Intune

Deploying Windows 10 Always On VPN with Microsoft IntuneWindows 10 Always On VPN is the replacement for Microsoft’s popular DirectAccess remote access solution. It provides the same seamless, transparent, always on remote connectivity as DirectAccess. Where DirectAccess relied heavily on classic on-premises infrastructure such as Active Directory and Group Policy, Always On VPN is infrastructure independent and is designed to be provisioned and managed using a Mobile Device Management (MDM) platform such as Microsoft Intune.

Intune and Always On VPN

Until recently, provisioning Windows 10 Always On VPN connections involved manually creating a ProfileXML and uploading to Intune using a custom profile. This has proven to be challenging for many, as the process is unintuitive and error prone.

A recent Intune update now allows administrators to create a basic Windows 10 Always On VPN deployment. Although it still has its limitations, it will go a long way to making the adoption of Always On VPN easier.

Prerequisites

Certificates must first be provisioned to all clients before deploying Windows 10 Always On VPN using Intune. In addition, if using a third-party VPN client, the VPN plug-in software must be installed prior to deploying the VPN profile.

Test VPN Connection

It is recommended that a test VPN connection be created on a client machine locally before deploying an Always On VPN profile using Intune. This allows the administrator to test connectivity and validate Extensible Authentication Protocol (EAP) settings. Once complete, run the following PowerShell commands to extract the EAP configuration settings to a file for later publishing with Intune.

$Vpn = Get-VpnConnection -Name [Test VPN connection name]
$Xml = $Vpn.EapConfigXmlStream.InnerXml | Out-File .\eapconfig.xml -Encoding ASCII

Deploying Always On VPN with Intune

Follow the steps below to deploy an Always On VPN connection using Intune.

Create a VPN Profile

  1. Open the Microsoft Intune management portal.
  2. Click Device configuration.
  3. Click Profiles.
  4. Click Create profile.

Deploying Windows 10 Always On VPN with Microsoft Intune

  1. Enter a name for the VPN profile.
  2. Enter a description (optional).
  3. From the Platform drop-down menu select Windows 10 and later.
  4. From the Profile type drop-down menu select VPN.
  5. In the Settings section click Configure.

Deploying Windows 10 Always On VPN with Microsoft Intune

Define VPN Profile Settings

  1. Click Base VPN.
  2. Enter a name for the connection.
  3. Enter a description and provide the Fully Qualified Domain Name (FQDN) of the VPN server. If it will be the default server select True and click Add.
  4. Enter a description and provide the FQDN for any additional VPN servers, as required.
  5. From the Connection type drop-down list choose the preferred connection type.
  6. In the Always On section click Enable.
  7. Select Enable to Remember credentials at each logon (optional).
  8. Click Select a certificate.
  9. Choose a client authentication certificate and click Ok.
  10. Paste the contents of eapconfig.xml (saved previously) in the EAP Xml field.
  11. Click Ok.

Deploying Windows 10 Always On VPN with Microsoft Intune

Define Additional Settings

You can also configure the following optional VPN settings using Intune.

  • Apps and Traffic Rules
  • Conditional Access
  • DNS Settings
  • Proxy
  • Split Tunneling

Deploying Windows 10 Always On VPN with Microsoft Intune

After configuring any required additional settings, click Create.

Assign VPN Profile

  1. Click Assignments.
  2. From the Assign to drop-down menu choose Selected Groups.
  3. Click Select groups to include.
  4. Choose an Azure Active Directory group to apply the VPN profile and click Select.
  5. Click Save.

Deploying Windows 10 Always On VPN with Microsoft Intune

Limitations

Although the ability to provision Always On VPN using Microsoft Intune without using a custom profile is welcome, it is not without its limitations. At the time of this writing, only Always On VPN user profiles can be configured. A device tunnel, which is optional, must be configured manually using a custom profile. In addition, the Intune user interface lacks the ability to define settings for the following parameters:

  • Exclusion routes
  • Name Resolution Policy Table (NRPT) exemptions
  • Lockdown mode
  • DNS registration
  • Trusted network detection
  • Custom IKEv2 cryptography policy

To make changes to the default settings for any of the above parameters, a ProfileXML must be created manually and provisioned with Intune using a custom policy.

Additional Information

Windows 10 Always On VPN Device Tunnel Step-by-Step Configuration using PowerShell

Windows 10 Always On VPN Certificate Requirements for IKEv2

Windows 10 Always On VPN and the Name Resolution Policy Table (NRPT)

Windows 10 Always On VPN Hands-On Training

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