Intro
Finding out how Windows decides if there is an Internet connection or not can be a challenge often posed by trying to do an Internet search comprised or words that are common and therefore used in many other contexts. I have to give credit to someone else who found most of these pertinent links that help explain how Windows decides whether or not your PC has an Internet connection.
What they don’t tell you
I think there are a lot more tests microsoft does than what they’ve documented. In my opinion, based on observation, in addition to the sites they recommend to whitelist, also whitelist
www.msftconnecttest.com
Some PCs get stuck in a loop requesting www.msftconnecttest.com/connecttest.txt indefinitely, which isn’t good for anyone.
Here’s one they don’t mention, of the same ilk:
ipv6.msftconnecttest.com/connecttest.txt
I’m thinking to just leave that one alone, unless you really are fully running on ipv6.
Now if you have a PAC file, what you’re going to see are accesses for
<PAC-file-address>/connecttest.txt
I don’t think that one’s documented either. I’m not yet sure how best to have the PAC file web server respond, where best means the reply which would make the PC most likely to decide Yes I really do have an Internet connection.
References and related
This Pulse Secure article is pretty good. You start with an Internet connection, then launch Pulse Secure vpn, then find you are told there is no longer an Internet connection. This explains why it might be, but in my opinion it is incomplete as it does not even consider the case where an authenticating proxy is the sole gateway to the Internet:
https://kb.pulsesecure.net/articles/Pulse_Secure_Article/KB43805
These are two more articles about VPN tunneling
https://community.pulsesecure.net/t5/Pulse-Desktop-Clients/Pulse-Secure-blocks-Windows-10-apps-from-internet-access/td-p/11944
https://docs.pulsesecure.net/WebHelp/PCS/8.3R1/Home.htm#PCS/PCS_AdminGuide_8.3/About_VPN_Tunneling.htm
network Location Awareness (NLA) and Network Connection Status Indicator (NCSI) are explained in these articles
https://support.microsoft.com/en-us/help/4494446/an-internet-explorer-or-edge-window-opens-when-your-computer-connects
https://support.microsoft.com/en-us/help/2778122/using-authenticated-proxy-servers-together-with-windows-8