Always On VPN Proxy Server Configuration

Always On VPN Proxy Server Configuration

Web proxy servers are not as common today as they once were, but a few organizations still leverage them to provide secure Internet access for their employees. Commonly they are used to inspect and control Internet traffic and to enforce acceptable use policies. Some organizations may wish to extend this protection to Always On VPN clients in the field by enabling force tunneling. Administrators can define a web proxy server for Always On VPN connections globally for web traffic or individual websites or domains.

VPN Proxy

A VPN web proxy server can be defined when the Always On VPN user tunnel connection uses force tunneling. Although you can still configure a VPN web proxy server with split tunneling enabled, it will not work. It is only functional when force tunneling is in use.

Administrators can configure a VPN web proxy server using the Microsoft Endpoint Manager UI or custom XML deployed with Endpoint Manager or PowerShell. Administrators can define a VPN web proxy server explicitly, or a proxy automatic configuration (PAC) file can be specified.

Note: VPN proxy server settings only work when force tunneling is enabled. Force tunneling is an unsupported configuration for the device tunnel, making the global proxy server setting for the device tunnel unsupported.

Proxy Autoconfiguration

Perform the following steps to configure a VPN web proxy server with a PAC file in Endpoint Manager.

  1. Expand the Proxy section in the Configuration settings of the Always On VPN configuration profile.
  2. Enter the URL for the PAC file in the Automatic configuration script field. Be sure to include the port number in the URL when using a non-standard port.
  3. Leave the Address and Port number fields blank.
  4. Choose Enable or Disable from the Bypass proxy for local addresses drop-down list.

To configure a VPN web proxy server with a PAC file using custom XML, include the following code between the <VPNProfile> and </VPNProfile> tags in the Always On VPN XML configuration file.

Explicit Proxy

Perform the following steps to configure an explicit VPN web proxy server in Endpoint Manager.

  1. Enter the IP address, hostname, or fully qualified domain name (recommended) in the Address field.
  2. Enter the port number in the Port number field.
  3. Choose Enable or Disable from the Bypass proxy for local addresses drop-down list.

To configure an explicit VPN web proxy server using custom XML, include the following code between the <VPNProfile> and </VPNProfile> tags in the Always On VPN XML configuration file.

Namespace Proxy

Administrators can also define VPN web proxy servers on a per-namespace or per-hostname basis. Namespace VPN proxy servers can be helpful for scenarios where routing public websites over the Always On VPN connection is required. Most commonly, this is necessary because the public website restricts access to the IP address of the on-premises Internet gateway.

A namespace VPN proxy server is implemented using a Name Resolution Policy Table (NRPT) rule. At the time of this writing, a bug in Microsoft Endpoint Manager prevents administrators from deploying this option using the UI.

As you can see here, administrators can specify a proxy server as part of an NRPT rule in the Endpoint Manager UI. Notice this section of the UI validates the proxy FQDN correctly.

Always On VPN Proxy Server Configuration

However, when you try to save the configuration profile, Endpoint Manager returns the following error.

“Unable to save due to invalid data. Update your data then try again: ProxyServerUri must be a valid URL or be empty.”

Interestingly, when entering a URL such as http://proxy.lab.richardhicks.net:8080/ in the Proxy field, the Endpoint Manager UI accepts it and successfully validates. But according to the VPNv2 Configuration Service Provider (CSP) reference, the value must be entered as an IP address. A hostname or FQDN also works based on my testing. Entering a URL as shown in the example above will not work at all.

With that, the only way to implement a namespace VPN web proxy server is to use custom XML. To do this, include the following code between the <VPNProfile> and </VPNProfile> tags in the Always On VPN XML configuration file.

Include the leading “.” to specify the entire domain, as shown above. Omit the leading “.” to specify an individual host (for example, app.richardhicks.com). Repeat this section for each additional host or domain, as required.

Caveat

Unfortunately, the Microsoft Internet Explorer web browser is the only browser that functions with the namespace VPN web proxy server. All modern web browsers, including Microsoft Edge, ignore the namespace proxy setting entirely, which seriously limits this feature’s usefulness in most organizations today.

Workaround

If routing a public website over the Always On VPN tunnel is required, adding its IP address(es) to the Always On VPN connection’s routing table is needed. However, doing this presents some unique challenges, as public websites frequently have many IP addresses, which are often dynamically changing. Also, it is common for public websites to pull content from many different domains or use Content Delivery Networks (CDNs), making the problem of identifying which IP addresses to add to the Always On VPN connection’s routing table even more challenging. Further, administrators must update the client configuration each a public website’s IP address changes, adding significant management overhead.

Summary

Routing client Internet traffic through an on-premises web proxy server for Always On VPN clients works well when force tunneling is enabled. Administrators can explicitly define a web proxy server or use a proxy automatic configuration (PAC) file. All web browsers work without issue in this scenario. Using a namespace proxy is only effective when browsing with Microsoft Internet Explorer. All modern web browsers, including Microsoft Edge, ignore namespace proxy settings.

Additional Information

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

Windows 10 VPNv2 Configuration Service Provider (CSP) Reference

Windows 10 Always On VPN Client DNS Server Configuration

Always On VPN DNS Registration Update Available

Always On VPN DNS Registration Update AvailableWhen configuring Always On VPN, administrators have the option to enable DNS registration for VPN clients. When this option is set, VPN clients will register the IP address assigned to their VPN interface in the internal DNS. This allows client devices to be managed using their hostname from the internal network whenever they are connected remotely.

DNS Registration

DNS registration is enabled in one of two ways, depending on how Always On VPN client devices are managed.

Intune

When using the native Microsoft Intune UI to manage Always On VPN profiles, DNS registration can be configured by selecting Enabled next to Register IP addresses with internal DNS in the Base VPN settings section.

Always On VPN DNS Registration Update Available

ProfileXML

When using custom ProfileXML with PowerShell, SCCM, or Intune, the administrator will define the RegisterDNS element to enable DNS registration.

Always On VPN DNS Registration Update Available

Known Issues

Some users have reported unexpected behavior when DNS registration is enabled. Specifically, under some circumstances the VPN client will register the IP address of the VPN network interface along with the IP address of its public network interface (Wi-Fi, Ethernet, etc.). However, the VPN client can only be managed using the VPN interface. If the VPN client’s hostname resolves to its public IP address, manage out will fail.

This appears to happen only when Name Resolution Policy Table (NRPT) rules are defined in Intune DNS settings, or if the DomainNameInformation element is defined in ProfileXML.

Always On VPN DNS Registration Update AvailableAlways On VPN DNS Registration Update Available

Resolution

Microsoft recently released fixes for this DNS registration issue for Windows 10. The fix for this issue is included in the following updates.

Windows 10 1803 – KB4507466
Windows 10 1809 – KB4505658
Windows 10 1903 – KB4505903

Additional Configuration

After installing the update, the following registry entry must be defined on each VPN client.

HKLM\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters\DisableNRPTForAdapterRegistration DWORD = 1

To enable this setting, open an elevated PowerShell window and run the following command.

New-ItemProperty -Path ‘HKLM:SYSTEM\CurrentControlSet\Services\Dnscache\Parameters\’ -Name DisableNRPTForAdapterRegistration -PropertyType DWORD -Value 1 -Force

Once complete, restart the client device for the changes to take effect. After validation testing is complete, the registry entry can be deployed to Always On VPN clients using Active Directory group policy preferences or Intune.

Additional Information

Deploying Windows 10 Always On VPN with Intune using Custom ProfileXML

Windows 10 Always On VPN Updates to Improve Connection Reliability

Windows 10 Always On VPN Device Tunnel Configuration using Microsoft Intune

Windows 10 Always On VPN Hands-On Training Classes

Always On VPN Updates to Improve Connection Reliability

Always On VPN Updates to Improve Connection ReliabilityA longstanding issue with Windows 10 Always On VPN is that of VPN tunnel connectivity reliability and device tunnel/user tunnel interoperability. Many administrators have reported that Always On VPN connections fail to establish automatically at times, that only one tunnel comes up at a time (user tunnel or device tunnel, but not both), or that VPN tunnels fail to establish when coming out of sleep or hibernate modes. Have a look at the comments on this post and you’ll get a good understanding of the issues with Always On VPN.

Recent Updates

The good news is that most of these issues have been resolved with recent updates to Windows 10 1803 and 1809. Specifically, the February 19, 2019 update for Windows 10 1803 (KB4487029) and the March 1, 2019 update for Windows 10 1809 (KB4482887) include fixes to address these known issues. Administrators are encouraged to deploy Windows 10 1803 with the latest updates applied when implementing Always On VPN. Windows 10 1809 with the latest updates applied is preferred though.

Persistent Issues

Although initial reports are favorable for these updates and based on my experience the effectiveness and reliability of Windows 10 Always On VPN is greatly improved, there have still been some reports of intermittent VPN tunnel establishment failures.

Possible Causes

During my testing, after applying the updates referenced earlier both device tunnel and user tunnel connections are established much more consistently than before the updates were applied. I did encounter some issues, however. Specifically, when coming out of sleep or hibernate, VPN connections would fail to establish. Occasionally VPN connections would fail after a complete restart.

NCSI

After further investigation it was determined that the connectivity failure was caused by the Network Connectivity Status Indicator (NCSI) probe failing, causing Windows to report “No Internet access”.

Always On VPN Updates to Improve Connection Reliability

Cisco Umbrella Roaming Client

In this instance the NCSI probe failure was caused by the Cisco Umbrella Roaming Client installed and running on the device. The Umbrella Roaming Client is security software that provides client protection by monitoring and filtering DNS queries. It operates by configuring a DNS listener on the loopback address. NCSI probes are known to fail when the DNS server is running on a different interface than is being tested.

Resolution

Microsoft released a fix for this issue in Windows 10 1709. The fix involves changing a group policy setting to disable interface binding when perform DNS lookups by the NCSI. You can enable this setting via Active Directory group policy by navigating to Computer Configuration > Administrative Templates > Network > Network Connectivity Status Indicator > Specify global DNS. Select Enabled and check the option to Use global DNS, as shown here.

Always On VPN Updates to Improve Connection Reliability

For testing purposes this setting can be enabled individual using the following PowerShell command.

New-ItemProperty -Path “HKLM:\SOFTWARE\Policies\Microsoft\Windows\NetworkConnectivityStatusIndicator\” -Name UseGlobalDNS -PropertyType DWORD -Value 1 -Force

Third-Party Software

As Always On VPN connectivity can be affected by NCSI, any third-party firewall or antivirus/antimalware solution could potentially introduce VPN connection instability. Observe NCSI operation closely when troubleshooting unreliable connections with Always On VPN.

Additional Information

Windows 10 1803 Update KB4487029

Windows 10 1809 Update KB4482887

Cisco Umbrella Roaming Client Limited Network Connectivity Warning

Network Connectivity Status Indicator (NCSI) Operation Explained