Using Microsoft Endpoint Manager (Intune), administrators can provision Always On VPN to devices that are Azure AD joined only. Users accessing on-premises resources from these devices can still use seamless single sign-on, making this deployment option popular for organizations moving to the cloud.
Short Names
After deploying Always On VPN to Windows 10 devices that are Azure AD joined only and configured to use client certificate authentication, administrators may find that users cannot access on-premises resources by their short name, such as \\app1. The connection fails and returns the following error message.
“Windows can’t find <servername/sharename>. Check the spelling and try again.”
FQDN
Interestingly, on-premises resources are accessible using their fully qualified domain name (FQDN), such as \\app1.corp.example.net.
Troubleshooting
Testing name resolution using the short name works as expected, and the resource is reachable at the network layer, as shown here.
Workaround
This issue is related to how Windows performs authentication when connected via VPN. To resolve this issue, edit the rasphone.pbk file and change the value of UseRasCredentials to 0. Rasphone.pbk can be found in the $env:AppData\Microsoft\Network\Connections\Pbk folder.
After updating this setting, restart the VPN connection for the change to take effect.
Proactive Remediations
While helpful for testing, editing rasphone.pbk manually obviously does not scale well. To address this, consider using Intune Proactive Remediations. Intune Proactive Remediations allows administrators to deploy detection and remediation PowerShell scripts to monitor specific settings and update them if or when they change. Proactive Remediations will ensure the setting is applied consistently across all managed endpoints.
GitHub Repository
I have created a new GitHub repository dedicated to PowerShell scripts for Endpoint Manager Proactive Remediations for Always On VPN. There you will find detection and remediation scripts for the UseRasCredentials settings change described in this article.
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.
Expand the Proxy section in the Configuration settings of the Always On VPN configuration profile.
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.
Leave the Address and Port number fields blank.
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.
Enter the IP address, hostname, or fully qualified domain name (recommended) in the Address field.
Enter the port number in the Port number field.
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.
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.
The Name Resolution Policy Table (NRPT) in Windows provides policy-based name resolution request routing for DNS queries. DirectAccess uses the NRPT to ensure that only requests for resources in the internal namespace, as defined by the DirectAccess administrator, are sent over the DirectAccess connection. DNS queries for all other namespaces are sent to the DNS servers defined on the client’s network interface.
Note: This behavior changes when force tunneling is enabled. In this case, all DNS queries are sent over the DirectAccess connection with the exception of the NLS and the DirectAccess server’s public hostname(s). If force tunneling is enabled, the configuration guidance described below is not required.
Split DNS
NRPT configuration is straightforward when the internal and external namespaces are unique. However, when split DNS is used, meaning when the internal and external namespaces are the same, DirectAccess configuration is more challenging. Typically, there may be many resources that should not go over the DirectAccess connection, such as public-facing web servers, email and unified communications servers, federation servers, etc. Without additional configuration, requests for all of these services would go over the DirectAccess connection. That may or may not be desirable, depending on the requirements of the implementation.
DirectAccess Server
One crucial public resource is the DirectAccess server itself. When using split DNS, the DirectAccess implementation’s public hostname will, by default, be included in the internal namespace. In this scenario, the DirectAccess client will fail to establish a connection to the DirectAccess server.
Troubleshooting
When troubleshooting failed connectivity, the output of ipconfig will show the IP-HTTPS tunnel interface media state as “Media disconnected”.
The output of Get-NetIPHttpsState will also return an error code 0x2AF9 with an interface status “Failed to connect to the IPHTTPS server; waiting to reconnect”.
To further troubleshoot this issue, examine the output of Get-NetIPHttpsConfiguration. Test name resolution of the FQDN listed in the ServerURL field. If the issue is related to NRPT configuration, the client will fail to resolve this name to an IP address. Testing from a non-DirectAccess client should resolve correctly, however.
NRPT Configuration
If split DNS is employed, it is necessary to include the DirectAccess server’s public hostname in the NRPT as an exemption. This will cause the DNS query for the public hostname to use public DNS servers, allowing the DirectAccess client to establish a connection successfully.
To resolve this issue, open the Remote Access Management console on the DirectAccess server, highlight DirectAccess and VPN under Configuration, and then click Edit on Step 3. Select DNS, and then double-click on an empty row in the table.
Enter the public hostname for the DirectAccess deployment in the DNS suffix field (the public hostname can be found by clicking Edit on Step 2). Do NOT specify a DNS server. Click Apply, click Next twice, and then click Finish.
Note: For multisite deployments, be sure to include the public hostname for each entry point in the enterprise. Also, if multisite is configured to use GSLB, include the GSLB hostname as well.
PowerShell
Alternatively, you can run the following PowerShell commands to automatically configure the NRPT for split DNS. For multisite deployments, be sure to run these commands on at least one DirectAccess server in each site.
The Name Resolution Policy Table (NRPT) in Windows provides policy-based name resolution request routing for DNS queries. DirectAccess uses the NRPT to ensure that only requests for resources in the internal namespace, as defined by the DirectAccess administrator, are sent over the DirectAccess connection. DNS queries for all other namespaces are sent to the DNS servers defined on the client’s network interface.
