A 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”.
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.
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
