DNS(Domain Name Server or System)

Hello Friends, In this blog post I am going to let you know about the DNS(Domain Name System or Server). In this post, you will see why do we need to have the DNS, and what is the function of DNS or how does it work?

The program rarely refers to mailboxes, hosts and other resources, by their binary network addresses. Instead of binary numbers, they use ASCII strings. Nevertheless, the network only understands the binary addresses, so some mechanism is required to convert the ASCII to network addresses.

In the past of ARPANET, there was simply a file, host.txt that contained all the hosts and their IP addresses. Each night, all the hosts would fetch it from the site at which it was maintained. This approach is well for a network of a few hundred large timesharing machines.

However, when thousands of workstations were connected to the net, everyone realized this approach could not continue to work forever. For one thing, the size of the file would become too large.

However, even more, important hostname conflicts would occur constantly unless names were centrally managed, Something unthinkable in a huge international network. To these problems, DNS(Domain Name System) was invented.

The essence of DNS is the invention of a hierarchical, domain-based naming scheme and a distributed database system for implementing the naming scheme.

The primary use of DNS is for mapping hostnames and email destinations to IP addresses but can also be used for another purpose. The DNS is a distributed database. It is used by TCP/IP applications. We use the term distributed because no single site on the internet knows all the information.

Each site maintains its own database of information and runs a server program that other systems across the internet (clients) can query. The DNS provides the protocols that allow the client and servers to communicate with each other.

On Unix hosts, the resolver is accessed primarily through two library functions, gethostbyname, and gethostbyaddr, which are linked with the application when the application is built.

The first takes a hostname and returns an IP address, and the second takes an IP and looks up a hostname. The resolver contacts one or more name servers to do the mapping.

The resolver is normally the part of the application. It is not part of the operating system kernel as are the TCP/IP protocols. RFC 1034 specifies the concept and facilities provided by DNS, and RFC 1035 details the implementation and specifications.

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