DNS Zone - Internet Infrastructure DNS Zones

Internet Infrastructure DNS Zones

The arpa top-level domain serves as a delegation zone for various technical infrastructure aspects of DNS and the Internet, and does not follow the registration and delegation system of the country and generic domains. The name arpa is a remnant of the ARPANET, one of the predecessor stages of today's Internet. Intended as a transition aid to the modern DNS system, deleting the arpa domain was later found to be impractical. It is now officially the acronym for Address and Routing Parameter Area. It contains sub-zones used for reverse resolution of IP addresses to host names (IPv4: in-addr.arpa, IPv6: ip6.arpa), telephone number mapping (ENUM, e164.arpa), and uniform resource identifier resolution (uri.arpa, urn.arpa). Although the administrative structure of this domain and its sub-domains is different, the technical delegation into zones of responsibility is similar and the DNS tools and servers used are identical to any other zone. Sub-zones are delegated by components of the respective resources. For example, 8.8.2.5.5.2.2.0.0.8.1.e164.arpa., which might represent an E.164 telephone number in the ENUM system, might be sub-delegated at suitable boundaries of the name. Examples of IP addresses in the reverse DNS zone are: 166.188.77.208.in-addr.arpa, resolving to the domain name www.example.com. In the case of IP addresses, the reverse zones are always delegated to the Internet service provider (ISP) to which the IP address block is assigned. When an ISP allocates a range to a customer, it usually also delegates the management of that space to the customer by insertion of name server resource records (pointing to the customers DNS facilities) into their zone. Notably, however, many ISPs serving individual end-users, such as homes or small businesses with only one IP address do not do so.