Domain Name System

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The Domain Name System (DNS) associates information with so-called domain names; most importantly, it serves as the "phone book" for the Internet by translating hostnames, e.g. www.example.com, into IP addresses, e.g. 208.77.188.166, allowing networking equipment to deliver information. It also stores other information, like the list of mail exchange servers that accept E-mail for a given domain.

The most basic task of DNS is to translate hostnames to IP addresses. In very simple terms, it can be compared to a phone book. DNS also has other important uses.

DNS makes it possible to assign Internet names to organizations independently of the physical routing hierarchy represented by the numerical IP address. Because of this, hyperlinks and Internet contact information can remain the same, whatever the IP routing, and can interpret a human-readable form (like "example.com"), which is easier to remember than the IP address 208.77.188.166. People take advantage of this when they recite meaningful URLs and e-mail addresses without caring how the machine will actually find and communicate with them.

The Domain Name System distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative server for each domain to keep track of its own changes, avoiding the need for a central registrar to be continually consulted and updated.

The Domain Name System consists of a hierarchical set of DNS servers. Each domain or subdomain has authoritative DNS servers that publish information about that domain and the name servers of any domains "beneath" it. The hierarchy of authoritative DNS servers aligns with the hierarchy of domains.