In the DNS Cache context, Primary and Secondary DNS servers refer to the two servers one would enter into their IP settings under “DNS Servers†as the computers to ask when the local machine doesn’t know the IP address for a given name. These servers can be run by the Carrier or on your own depending on your expertise, but typically the Carrier runs these servers for you.
Outdated uses of these terms refer to Authoritative DNS. Initially the intentio n was for a client to query the Primary DNS server and if a response weren’t received, the Secondary DNS server would be queried. In reality, any number of Authoritative DNS servers can be listed for a domain name, which should be queried in no particular order.
