Open your Command Prompt from the Start menu (or type “Cmd” into the search in your Windows task bar). Next, type ipconfig/all into your command prompt and press Enter. Look for the field labeled “DNS Servers.” The first address is the primary DNS server, and the next address is the secondary DNS server.
What if there is no secondary DNS?
Provides redundancy in case the primary DNS server goes down. If there is no secondary server, when the primary fails, the website will become unavailable at its human-readable domain name (although it will still be accessible by its IP).
