What Is a DNS Zone?

Organization

All the DNS zones are organized into a hierarchical, tree-like structure, with cascading lower-level domains, which collectively form the DNS namespace. In other words, a DNS domain is a branch of the DNS namespace, and a DNS zone is part of the subtree that constitutes the domain. The terms domain and zone are sometimes used interchangeably, but while each DNS zone is anchored at a specific DNS domain node, zones are not domains.

The domain Somecompany.com may contain all of the data for Somecompany.com and subdomains, such as Marketing.somecompany.com, Production.somecompany.com and Sales.somecompany.com. The zone Somecompany.com, on the other hand, contains only data for Somecompany.com, plus references to the name servers for the subdomains. A single name server can, however, be authoritative for many zones or divide part of its zone and delegate it to other servers. Each server answers queries about hosts in its zone.

Each DNS zone requires a primary, or master, name server and a secondary name server. The primary name server maintains a DNS zone file, which contains information about the zone and database records for the distributed DNS database, known as resource records. Any updates are made to the primary name server, while the secondary name server copies, or mirrors, data stored on the primary name server. The mechanism for updating the primary and secondary name servers is known as DNS zone transfer, which is an answer to a DNS query to list all the DNS information for a domain. DNS zone transfer is one of the weak points in DNS security.

A DNS zone file contains a series of standard configuration settings, which are searched when someone requests a forward translation, from a domain name to an Internet address, or a reverse translation, from an Internet address to a domain name. Key record types in a DNS zone file include a start of authority (SOA) record, which is the first record in the file and provides settings for the primary name server in the zone, and name server (NS) records, one for each name server within the zone.