Domain Name System (DNS often denoted) is a service used to resolve host names into IP addresses and vice versa. The service is realized through a distributed database consisting of the DNS server.
The name denotes the DNS protocol that governs the operation of the service, the programs that implement the server on which they run, all of these servers that cooperate to provide the service.
DNS names, or "domain names", are one of the most visible features of the Internet.
There is confusion about the expansion of the definition: S is often interpreted as service, but the correct definition is system. The operation to convert a name into an address is called DNS resolution, convert IP address into a name is called reverse resolution.
The ability to assign a name easy to store text to a server (such as a world wide web site) greatly improves the use of the service, because human beings are easier to remember names textual (while the hosts and routers can be reached using numeric IP addresses). For this reason, the DNS is fundamental to the wide spread of internet even among non-technical users, and is one of its most visible.
You can assign several names to the same IP address (or vice versa) to represent the different services or functions provided by the same host (or hosts that provide the same service) This flexibility is useful in many cases. A domain name consists of a series of strings separated by periods, for example it.wikipedia.org. Unlike IP addresses, where the most important number is the first from the left, in a DNS name the most important part is the first from the right. This is called top-level domain (or TLD, Top Level Domain), for example. Org or. Com.
A second-level domain consists of two parts, for example, wikipedia.org, and so forth. Each element specifies a further subdivision. When a second level domain is registered all'assegnatario, has the right to use domain names related to subsequent levels as it.wikipedia.org (third-level domain) and others as some.other.stuff.wikipedia.org ( fifth level domain), and so forth.