If I remember right the Windows Network Connectivity Status Indicator (NCSI) is running multiple tests to check if the client is connected to the internet.
- The following URL is used for the first test: https://www.msftconnecttest.com
- If the URL is reachable from the client a HTTP Get-Request for https://www.msftconnecttest.com/connecttest.txt is sent.
- If this is successfully, NCSI will try to resolve the DNS name dns.msftncsi.com.
- If the response is "131.107.255.255" the test is successful and the indicator in the Task Bar will show "Internet access".
So you should add https://www.msftconnecttest.com to your white-list in the Firewall.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten