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Okay now my friend would post about understanding DNS. After his dipostingan before I had
Discussing about the web server. Do not worry at length, please refer to.

Domain Name System (DNS) is to distribute the database system used to search the computer name (name resolution) in a network that uses TCP / IP (Transmission Control Protocol / Internet Protocol). DNS is used in applications connected to the Internet such as web browsers or e-mail, which helps control a computer to map host names to IP addresses.
Besides being used on the Internet, DNS can also be implemented to a private network or intranet where the control has advantages such as:
Easy, DNS is easy because the user no longer be bothered to remember the IP address
an adequate host computer name (Computer name).
Consistently, the IP address of a computer host name can be changed but not changed.
Simple, user uses only one domain name to search both the Internet and the Intranet.

DNS can be equated with a phone book function. Where every computer on the network the Internet has a host name (computer name) and Internet Protocol (IP) address. In general, each client that will connect one computer to another computer, will use the host name. Then your computer will contact the DNS server to check the host name you requested is how the IP address. IP addresses are used to connect your computer with other computers.

History of DNS
Before using control, computer networks using HOSTS files that contain information from the computer name and IP address. On the Internet, this file is managed centrally and in each location must copy the latest version of HOSTS files, from here you can imagine how difficult it if there is the addition of a computer on the network, then we should copy the latest version of this file to any location. With the ever expanding internet network, it is more troublesome, eventually created a solution where the DNS is designed to replace the function of HOSTS files, with an excess of unlimited database size, and the performace is good. DNS is an application services on the Internet that translates a domain name to IP address. For example, the www for use on the Internet, then typed domain name, for example: yahoo.com then it will be mapped to an IP eg 202.68.0.134. So in analogy to the DNS can use the phone book, where people we know by name to reach him we have to dial a telephone number on the telephone. Exact match, the host computer sends queries in the form of a computer name and domain name server to the DNS, then the control is mapped to IP addresses.

Structure of DNS
Root-Level Domains
Domain is determined based on the existing level of ability in a hierarchical structure called a level. The top level in the hierarchy is called the root domain. Root domain are expressed based on a period in which the symbol for the root domain is (".").
Top-Level Domains
In the sections below is an example of top-level domains:
com: Commercial Organizations
edu: educational institution or university
org: Non-profit Organizations
net: Networks (Internet backbone)
gov: government non-military organizations
mil: military government Organizations
num: No telephone
ARPA: Reverse DNS
xx: two-letter country code for (id: Indonesia, sg: singapore, au: Australia, etc.)
Top-level domains can contain the second-level domains and hosts.

Second-Level Domains
Second-level domains can contain hosts and other domains, called subdomains. For example: Domain Bachelors, there bujangan.com computer (host) such training.bujangan.com server1.bujangan.com and subdomains. Subdomains training.bujangan.com there is also a computer (host) as client1.training.bujangan.com.

Host Names
Domain name used with the host name will create a fully qualified domain name
(FQDN) for each computer. For example, if there is fileserver1.detik.com, where fileserver1 is the host name and domain name are detik.com.

How DNS Work?
The function of DNS is to translate computer names to IP addresses (mapped). DNS client is called resolvers and DNS servers called name servers. Resolvers or client sends a request to name server queries. Name server will process by checking the local DNS database, or contact another name server will send a failure message if it turns out a request from a client not found. The process is called the Forward Lookup Query, which is a request from the client by mapping the computer name (host) to the IP address.

 Resolvers Send Queries to Name Servers
Check to the local name server database, or contact another name server, if found will be notified to the resolvers if not will send failure message
Resolvers contacted the destination host using the IP address given name server.

Conclusion
DNS is the result of the development of methods of finding host names to IP addresses on the Internet. On the DNS client (resolver) sends queries to the Name Server (DNS). Name Server will accept requests and map names to IP address Computer Domain Name Space is a hierarchical grouping consisting of a root-level domains, the top-level domains, the second-level domains and host names.