When a network configuration change is detected, Windows will use the Network Connection Status Indicator (NCSI) technology to:
- Check the connectivity to the Intranet
- Check the connectivity to the Internet
NCSI determines connectivity using the following process:
- The adapter will send a DNS query for www.msftconnecttest.com and www.ipv6.msftconnecttest.com(for dual stack machines)
- If successful, an http GET request is sent for www.msftconnecttest.com/connecttest.txt.
- If the client receives an HTTP 200 OK response, NCSI sends a standard DNS query for an A record of dns.msftncsi.com and subsequently a standard DNS query is sent for an AAAA record of dns.msftncsi.com.
If the DNS request in step 1 fails, or the HTTP response is anything other than HTTP 200 OK in step 2, then the LAN adapter and/or the Pulse virtual adapter will display a status of "No Internet access" and applications such as Microsoft Office 365 will report network access failures and not connect.