The Domain Name System (DNS) is a completely decentralized and distributed database that maps easy-to-remember, fully-qualified domain names (for example, www.infoweapons.com) to IP addresses, which are far more difficult to remember. In many ways it is like a telephone directory, which matches names to numbers. DNS can also translate IP addresses into domain names (a process called reverse lookup). It also provides information on the preferred servers for certain services of a particular domain (such as e-mail or LDAP servers).

The DNS database and the software used to run it are distributed literally across millions of DNS servers (sometimes called name servers) throughout the world. Some DNS servers are authoritative for a particular domain, which means that they are responsible for the DNS data for that domain and answer queries about that domain directly. Other, non-authoritative DNS servers know how to get the mappings for nodes in that domain from the domain’s authoritative DNS server, or from another server that has cached the required data from a previous query.

An authoritative server can also assign other DNS servers as authoritative for its subdomains. The DNS database is therefore hierarchical, with some name servers being authoritative for a domain and containing the locations of other name servers assigned to subdomains and other nodes within a domain name space. At the top of this hierarchical, distributed database are the root servers, which are the authoritative name servers for Top Level Domains (such as com or org).