A DNS zone is a specific portion of the DNS namespace in the Domain Name System (DNS), which is managed by a specific organization or administrator. A DNS zone is an administrative space that allows for more granular control of the DNS components, such as authoritative nameserver. The DNS is broken up into many different zones, which are distinctly managed areas in the DNS namespace. DNS zones are not necessarily physically separated from one another, however, a DNS zone can contain multiple subdomains and multiple zones can exist on the same server. The domain namespace of the Internet is organized into a hierarchical layout of subdomains below the DNS root domain. The individual domains of this tree may serve as delegation points for administrative authority and management. However, usually, it is furthermore desirable to implement fine-grained boundaries of delegation, so that multiple sub-levels of a domain may be managed independently. Therefore, the domain name space is partitioned into areas (zones) for this purpose. A zone starts at a domain and extends downward in the tree to the leaf nodes or to the top-level of subdomains where other zones start. A DNS zone is implemented in the configuration system of a domain name server. Historically, it is defined in the zone file, an operating system text file that starts with the special DNS record type Start of Authority (SOA) and contains all records for the resources described within the zone. This format was originally used by the Berkeley Internet Name Domain Server (BIND) software package and is defined in RFC 1034 and RFC 1035. Domains and zones Most top-level domain name registry operators offer their name spaces to the public or to entities with mandated geographic or otherwise scoped purpose for registration of second-level domains. Similarly an organization in charge of a lower level domain may operate its name space similarly and subdivide its space. Each registration or allocation of subdomain space obligates the registrant to maintain an administrative and technical infrastructure to manage the responsibility for its zone, including sub-delegation to lower-level domains. Each delegation confers essentially unrestricted technical autonomy over the allocated space. An area of one or more subdomains that has been delegated for management is called a DNS zone. A zone always starts at a domain boundary to include all leaf nodes (hosts) in the domain, or it ends at the boundary of another independently managed zone.