A primary server for a zone is the server that stores the definitive versions of all records in that zone.
It is identified by start-of-authority (SOA) resource record.
DNS provides a mechanism whereby the primary for a zone can notify all the known secondaries for that zone when the contents of the zone have changed.
The contents of a zone are either manually configured by an administrator, or managed using Dynamic DNS.
Name servers can also be configured to give authoritative answers to queries in some zones, while acting as a caching name server for all other zones.
An authoritative name server can either be a primary server (master) or a secondary server (slave).
If the server for a zone is not also authoritative for its parent zone, the server for the parent zone must be configured with a delegation for the zone.) that are authoritative for the zone that contains the domain.
That server provides the answer to the question, or definitively says it can't be answered, and the caching resolver then returns this response to the client that asked the question.The most important function of DNS servers is the translation (resolution) of human-memorable domain names and hostnames into the corresponding numeric Internet Protocol (IP) addresses, the second principal name space of the Internet which is used to identify and locate computer systems and resources on the Internet.The top hierarchy of the Domain Name System is served by the root name servers maintained by delegation by the Internet Corporation for Assigned Names and Numbers (ICANN).Because they can answer questions more quickly, they also increase the performance of end-user applications that use the DNS.Recursive name servers resolve any query they receive, even if they are not authoritative for the question being asked, by consulting the server or servers that are authoritative for the question.Caching name servers (DNS caches) store DNS query results for a period of time determined in the configuration (time-to-live) of each domain-name record.DNS caches improve the efficiency of the DNS by reducing DNS traffic across the Internet, and by reducing load on authoritative name-servers, particularly root name-servers.Caching name servers are often also recursive name servers—they perform every step necessary to answer any DNS query they receive.To do this the name server queries each authoritative name-server in turn, starting from the DNS root zone.The authority, resolving and caching functions can all be present in a DNS server implementation, but this is not required: a DNS server can implement any one of these functions alone, without implementing the others.Internet service providers typically provide caching resolvers for their customers.