A resolver looks up the resource record information associated with nodes. A resolver knows how to communicate with name servers by sending DNS queries and heeding DNS responses.
A DNS query may be either a recursive query or a non-recursive query:
- A non-recursive query is one where the DNS server may provide a partial answer to the query (or give an error). DNS servers must support non-recursive queries.
- A recursive query is one where the DNS server will fully answer the query (or give an error). DNS servers are not required to support recursive queries.
The resolver (or another DNS server acting recursively on behalf of the resolver) negotiates use of recursive service using bits in the query headers.
Resolving usually entails iterating through several name servers to find the needed information. However, some resolvers function simplistically and can only communicate with a single name server. These simple resolvers rely on a recursive query to a recursive name server to perform the work of finding information for them.
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