Resource Records and Zones
To resolve names, servers consult their zones (also called DNS database files or simply db files). The zones contain resource records (RRs) that make up the resource information associated with the DNS domain. For example, some resource records map friendly names to IP addresses, and others map IP addresses to friendly names.
Certain resource records not only include information about servers in the DNS domain, but also serve to define the domain by specifying which servers are authoritative for which zones. These resource records, the SOA and NS resource records, are described in more detail later in this section.