(also DNS iteration)
In an iterative DNS query, if the DNS server has no relevant DNS records in its cache, it refers the DNS client to another DNS server. The process repeats (iterates) until one of the queried DNS servers returns the correct IP address for the domain.
Query to root server (first step): One of 13 root servers in the world extracts the top-level domain from the query and provides details for the next server.
Query to authoritative name server (last step): The ANS returns the correct IP address (or NXDOMAIN if it cannot find the domain) to the DNS resolver.