Editing Domain Name System (section)

===DNS resolvers===
The [[Client-side|client side]] of the DNS is called a DNS resolver. A resolver is responsible for initiating and sequencing the queries that ultimately lead to a full resolution (translation) of the resource sought, e.g., translation of a domain name into an IP address. DNS resolvers are classified by a variety of query methods, such as ''recursive'', ''non-recursive'', and ''iterative''. A resolution process may use a combination of these methods.<ref name="rfc1034" />

In a ''non-recursive query'', a DNS resolver queries a DNS server that provides a record either for which the server is authoritative, or it provides a partial result without querying other servers. In case of a [[#Record_caching|caching DNS resolver]], the non-recursive query of its local [[Name server#Caching name server|DNS cache]] delivers a result and reduces the load on upstream DNS servers by caching DNS resource records for a period of time after an initial response from upstream DNS servers.

In a ''recursive query'', a DNS resolver queries a single DNS server, which may in turn query other DNS servers on behalf of the requester. For example, a simple stub resolver running on a [[home router]] typically makes a recursive query to the DNS server run by the user's [[ISP]]. A recursive query is one for which the DNS server answers the query completely by querying other name servers as needed. In typical operation, a client issues a recursive query to a caching recursive DNS server, which subsequently issues non-recursive queries to determine the answer and send a single answer back to the client. The resolver, or another DNS server acting recursively on behalf of the resolver, negotiates use of recursive service using bits in the query headers. DNS servers are not required to support recursive queries.

The ''iterative query'' procedure is a process in which a DNS resolver queries a chain of one or more DNS servers. Each server refers the client to the next server in the chain, until the current server can fully resolve the request. For example, a possible resolution of www.example.com would query a global root server, then a "com" server, and finally an "example.com" server.