Before the invention of DNS each computer system on the network retrieved a file called HOSTS.TXT from a computer at SRI. This HOSTS.TXT maps the names to the numerical addresses. Now a day’s also this file exists in on few computers which contains modern operating systems. To connect to any system that supports Internet Protocol (IP), we have to know the IP address of the remote system before connecting to that system. The IP address represents 32-bit number which is designed by designers of TCP/IP that explains where the remote system is there on the network, which is called as IPv4 (Internet Protocol). Due to huge development of internet we are running down of addresses, so to rectify this a new system is designed which is known as IPv6 (Internet Protocol) which has 128-bit number for the IP address.
These IP addresses are represented as below in IPv4:
192.168.179.1 – decimal notation
11000000.10101000.10110011.00000001 – binary representation
The above shown is IPv4 address represented in decimal notation and binary representations.
This IPv4 consists of 32 bit numbers and this restricts the address space to 232 distinctive addresses. In decimal notations of address each part contains 8 bits of address which is known as octet. In decimal notations each number is separated by dot character. Some authorities maintaining distinctive host names for the internet. They maintain a particular file and web sites repeatedly update that file by their host names and IP address mappings to add in that file. These days the internet grown rapidly and the problem is the file become unmanageable because the host names must to be distinctive in the internet and these days the distinctive host names are not possible due to rapid growth of internet. The need for such things as a hierarchical naming structure and distributed management of host names paved the way for the creation of a new networking protocol that was flexible enough for use on a global scale. What evolved from this
The requirements for such things (i.e., hierarchical naming structure and distributed management) of host names covered the way for the making of new networking protocol which is flexible to use. What evolved from this is an Internet distributed database that maps the names of computer systems to their respective numerical IP network addresses.
The DNS supports host names to network address resolution, well-known as forward resolution as well as it supports network address to host names resolution known as inverse resolution. This is evolved as a critical component of the internet because of its ability to map human memorable system names into computer network numerical addresses. Using of IP addresses to connect to other computers in network is not very user-friendly representation. Thus the DNS is closely depends upon to get back an IP address by just referencing computers Fully Qualified Domain Name (FQDN). A Fully Qualified Domain Name (FQDN) is essentially a DNS host name. So by this we can convert the host name to IP address easily.
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As a tree is traversed in an ascending manner (i.e., from the leaf nodes to the root), the nodes become increasingly less specific (i.e., the leftmost label is most specific and the right most label is least specific). Typically in an FQDN, the left most label is the host name, while the next label to the right is the local domain to which the host belongs. The local domain can be a subdomain of another domain. The name of the parent domain is then the next label to the right of the sub domain (i.e., local domain) name label, and so on, till the root of the tree is reached.
The Internet keeps two most important namespaces, the domain name hierarchy and the Internet Protocol (IP) address system. The Domain Name System (DNS) keeps the domain namespace and provides conversion services among these two namespaces. Internet name servers and a communications protocol execute the Domain Name System. A DNS name server is a kind of server that which keeps DNS records, such as address records, name server records for a domain name and returns answers for the queries next to the database.
Internet Protocol
The Internet Protocol is a method or protocol by which data or information is transferred from one PC to other on Internet. Each PC on Network has at least one unique IP address to identify that PC on Internet to transfer or receive information or data. While we are transferring the data to other PC the data is divided into small chunks called packets. Each of these packets consists both the receiver and senders Internet Address. Each and every packet is sent to gateway computer first which can understands each and every part of Internet. The gateway PC reads the destination’s IP address and forwards the packet to the nearest gateway PC to transfer the packet to the destination to reduce the transfer time. Each and every packet is transferred to the destination in different order because the some packets are sent through different routes across internet. So the packets can arrive to the destination in different orders. So the Internet Protocol does not take any action over this order. The Transmission Control Protocol will takes necessary action over these packets and it puts them in correct order to retrieve appropriate information or data which is sent. Internet Protocol is a connection less protocol. This means there is no connection between the computers all the time. (http://searchunifiedcommunications.techtarget.com/sDefinition/0,,sid186_gci214031,00.html)
The Domain Name Space
The domain name space contains a hierarchy of domain names. Each node in the hierarchy may contain zero or more resource records which cleave to information associated with the domain name. The tree is sub divided into zones starting at root region. A DNS zone contains a collection of connected nodes confidently served by a reliable name server.
Figure1:- Domain Name Space
A domain name consists of one or more parts, technically called as labels and they are added and separated by dots such as universe.com
For example if we take the domain name as www.universe.com then com is the top level domain and universe is the sub domain for the domain called com and www is the sub domain of universe.com domain. (http://searchwindevelopment.techtarget.com/definition/domain-name)
Few limitations for the domain names
Every label may hold up to 63 characters.
The complete domain name may limits to 253 characters of length.
In the each label the characters used are from set of ASCII characters and this includes a to z, A to Z , 0 to 9 and hyphen. So this rule called as LDH rule.
The labels do not start with hyphen and it does not end with hyphen.
Authoritative name server
This is a server that which gives responses that have been configured by unique source. the regular DNS queries obtained to the name server are responded back by a domain administrator or by dynamic DNS methods. This server returns responses to requests about domain names that have been particularly configured by administrator. This server can be a master server or slave server. This master server saves the unique copies of all zone records. A slave server uses DNS protocol in communication with its master to use automatic updating mechanism to maintain identical copy of the master records.
Name servers
The distributed database system maintains Domain Name System, which uses client-server model. The nodes of this database are the name servers. Every domain has at least one authoritative DNS server that gives details in relation to that domain and the name servers of any domains subsidiary to it.
DNS Components
The DNS has three main components, the database, the server and the client. The database is a distributed database and is comprised of the Domain Name Space, which is basically the DNS tree. The server is commonly referred to as a name server. This is normally liable for managing some part of the Domain Name Space and for supporting clients in identifying information within the DNS tree. The client component of DNS normally contains software routines called as functions, which are responsible for requesting information from the Domain Name Space on behalf of an application.
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