Hi fa-br-ice,
Are you trying to create an internal NCSI server by customizing the following registry key?
HKLM\SYSTEM\CurrentControlSet\Services\NlaSvc\Parameters\Internet
Value: ActiveWebProbeHost (REG_SZ) defaults to “www.msftncsi.com”
Value: ActiveWebProbePath (REG_SZ) defaults to “ncsi.txt”
Value: ActiveWebProbeContent (REG_SZ) defaults to "Microsoft NCSI"
I found an article could help you consider your current condition. Please let me know if it is help.
https://blogs.technet.microsoft.com/networking/2012/12/20/the-network-connection-status-icon/
Best regards.
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