Authoritative servers

An authoritative server is the authority for its zone. It queries and is queried by other name servers in the DNS. The data it receives in response from other name servers is cached. Authoritative servers are not authoritative for cached data.

There are two types of authoritative servers: master (primary) and secondary. Each zone must have only one master name server, and it should have at least one secondary name server for backup purposes to minimize dependency on a particular node. Calling a particular name server a master or secondary server is misleading. Any given name server can take on either or both roles, as defined by the conf file.

The zone data updates and maintenance are reflected in the master name server and the changes are then reflected in secondary name servers. Both master and secondary name servers are authoritative for a zone.

The zones of authority are arranged in a hierarchy based on the domain origin components. A special zone known as the root exists at the top of the domain name hierarchy in a network. The root zone contains a list of all the root servers. For example (see Figure 1), in the Internet, the root name servers store information about nodes in the root domain, and information about the delegated domains, such as com (commercial), edu (education), and mil (military). The root name servers store the names of name servers for each of these domains, which in turn store the names of name servers for their delegated subdomains.

TCP/IP applications contact a name server whenever it is necessary to translate a domain name into an IP address, or when information is required about a domain. The name server performs the translation if it has the necessary information. If it does not have the necessary information, the name server can contact other name servers, which in turn can contact other name servers. This process is called a recursive query. Alternatively, a name server can return the address of another name server that might hold the requested information. This is called a referral response to a query. Name server implementations must support referrals, but are not required to perform recursive queries. See Resolvers for more information about query responses.