DNS

Many Internet users are probably not aware of how the Domain Name System (DNS) works. However, the DNS is absolutely essential for using the Internet in a comfortable and easy way. Only this system enables a website to be visited by entering a URL such as www.denic.de or an e-mail to be sent to info@denic.de. Computers within a TCP/IP network such as the Internet address each other by IP addresses, whereas humans would have great difficulties in remembering thousands of numeric combinations.  

Until the mid-1980s, the linking of computer names and IP addresses was implemented by a simple computer file. The so-called HOST.TXT file (cf. RFC952) was maintained centrally and all changes (updates) had to be sent to that central location, from where they were then redistributed to all the hosts.
As the numbers of Internet users started to grow faster and faster, this system very soon reached its limits. Both the volume of data to keep the HOST.TXT file up to date and the administrative outlay grew continuously, and, at the same time, the chances of guaranteeing the uniqueness of computer names and keeping the data fully up to date at all locations throughout the network diminished.

One solution to these problems came along in the form of the Domain Name System, a hierarchical, decentralized system for the administration of names, which shares out responsibilities and ensures the uniqueness of the names. 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. 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 in a network acts as the e-mail server for the domain concerned or what a domain's name servers are called.