The Domain Name System (DNS)
The Domain Name System is a directory service on the Internet. It is like a telephone book distributed across the world, in which one or several telephone numbers (IP addresses) are listed for a name. Providing this service, the DNS is an indispensable prerequisite for reaching services on the Internet (such as online shopping or online travel booking). Because only the DNS enables a user to get access to a particular website by entering an URL like https://www.denic.de or to send an e-mail to firstname.lastname@example.org.The participants on the Internet are computers. To be able to communicate with each other, each computer has a unique IP address, such as 192.0.2.122 or even 2001:db8:85a3::8a2e:370:7334. The DNS will map the ULR (e.g. www.denic.de) the user has entered to this combination of numbers.
How Does the DNS Work?
The Domain Name System is a redundantly operated, hierarchical, and decentralized system for the administration of names. It shares out responsibilities and ensures the uniqueness of the names on the separate hierarchical layers. This is done through a tree-like structure, known as the "name space". The tree's "root" divides into various branches, the familiar Top Level Domains, such as .de, .net or .com. These branch out further into so-called Second Level Domains, and so on and so forth (see Figure).
The DNS, however, does much more than just linking computer names to IP addresses. It can also be used for saving and retrieving further information about the services linked to a domain. A DNS query is able to find out, for instance, which computer acts as the e-mail server for the domain concerned or what a domain's name servers are called.