What type of DNS server is not configured with any zones, but fields DNS queries and sends iterative queries to upstream DNS servers and stores the results?

Authoritative server.

Explanation:

DNS is an application layer protocol of the OSI and the TCP/IP suite network model. It is called the domain name server, as it helps client host to lookup or resolve domain name to IP addresses. An example of a DNS server is the authoritative server.

The authoritative server is a zone-less server that fields DNS queries and sends iterative queries to other DNS servers and stores the result.

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