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                 2.29 DOMAIN NAME SYSTEM (DNS)

              The Domain Name System (DNS), which allows computers to communicate with one another and send email or display
              webpages, is at the heart of how the Internet works.

              The DNS (Domain Name System) is a database that maps domain names to IP addresses. The hierarchical domain
              namespace that we mentioned earlier is the foundation of DNS. DNS is a distributed directory that provides the
              framework for a single, worldwide domain name directory. This directory is made up of tens of thousands of servers
              owned by tens of thousands of companies all around the world.

              DNS Services

              The services provided by DNS are as follows:

              Ð ÐHost Aliasing: One or more alias names can be assigned to a host with a complicated hostname. An application can
                 use DNS to get the canonical hostname for a specified alias hostname as well as the host's IP address.

              Ð ÐMail Server Aliasing: A mail application can use DNS to find out the hostname for an alias hostname as well as the
                 IP address of the host.

              Ð ÐLoad Distribution: DNS is also used to distribute load among duplicated servers.
              Types of Name Servers

              The names given to the machines must be carefully chosen from a name space, with complete control over the name-
              to-IP address mapping. Flat name spaces and hierarchical names are the two forms of name spaces.
                                Flat Name Spaces                                  Hierarchical Name Space
               A name in a flat name space is just a string of      Each name in a hierarchical name space is made up of
               characters with no structure.                        numerous parts.
               An address is assigned to a name in this space.      The first section identifies the organization's nature,
                                                                    the second part specifies the organization's name, the
                                                                    third part defines the organization's department, and
                                                                    so on.

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