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The Domain name system (DNS) is a distributed database providing a hierarchical naming system for identifying hosts on the internet. DNS wasdeveloped to slove the problems that arose for identifying hosts on the internet grew dramatically in early 1980's. the DNS database is a tree structure called the domain name space.Each domain (node in tthe tree structure) is named and and can contain sub-domains. The domain name identifies the domain's position in the database in relation to its present domain.A period (.) seprates each part of the names for the network nodes of the DNS domain.For example, theDNSdomain name csu.edu specifies the csu sub domain whose parent is the edu domain; csu.com specifies the csu sub domain whose parent is the com domain.

Top -level Domais:

The root and top-level domains of the DNS database are managed by the inter NIC. The top-level domain name are divided into three main areas:

1). Organizational domains (3-character name)

2). Geographical domains (2-character country codes found in ISO3166)

3). The in-addr.arpa.domain (a special domain used for address to name mapping)

Organizational domain name were originally used in the United States, but as the internet began to grow internationally, it became obvious that an organizational division was inadequate for a global entity.Geographical domain names were then introduced . Even though a ".us" country domain exists,domain name in the united states are still predominantly organizational.