What is www.msftncsi.com?
If you are running a firewall one of the most common sites you’ll run across is www.mstfncsi.com. This is because the url www.msftncsi.com is generally used by Windows machines to verity that there is network connectivity. A Windows machine (Windows 8, Windows 7 and even Windows Vista I believe) will try to get a file from a web server to determine if there is network connectivity. There are two tests that a Microsoft Windows Client will perform to determine if there is outside connectivity to the Internet. The first one of such tests is being able to resolve msftncsi.com successfully and then retrieve a text time. The second test is more basic and it tries to retry said file directly via an IP address instead of using your DNS server to resolve those addresses. This way Windows can determine if you are having issues with your DNS, router, etc. If it determines successfully that there is network connectivity you’ll see on your network card status indications if there is IPv4 Connectivity and IPv6 Connectivity:
In my case, I have only IPv4 Connectivity as my Internet Service Provider (ISP) does not support IPv6 yet.
Below are a few details of the URLs that are used. As you might imagine there is an ipv6 and an ipv4 address:
- http://www.msftncsi.com/ncsi.txt is used to verify IPV4 connectivity and DNS resolution
- http://ipv6.msftncsi.com/ncsi.txt is used to verify IPV6 connectivity and DNS resolution
Besides that there are some IP addresses it uses to try to verify connectivity without using DNS resolution. Below are a few: