How does DNS Work in Internet?

 The hierarchical system of domain names in Internet has been broadly classified into

three categories:

1. Generic domain names
2. Country based domain names
3. Inverse domains
   
   

The three-character top-level names are called the generic domains or the
organizational domains. The generic domain defines registered hosts in accordance
with their behavior for example, yahoo.com uses ‘com’ as top level name as it
signifies that yahoo is a commercial organization. Table 1 shows some of the top-level domains of today’s Internet domain hierarchy.

Domain  Name	Meaning
Com	Commercial organizations
Gov	Government institutions
Org	Non-profit organizations
Mil	Military groups
Edu	Educational institutions
Net	Major network support centers
Int	International organizations

There are also top-level domains named for each of the ISO 3166 international 2-
character country codes (e.g., zw for Zimbabwe). These are called the country
domains. Many countries have their own second-level domains underneath, which
parallel the generic top-level domains.

As it is a simple matter in principle to search the database for an IP address with its
symbolic name (because of the hierarchical structure), the reverse process cannot
follow the hierarchy. Therefore, there is another namespace for the reverse mapping
called Inverse domain. The information about the inverse domain is always stored in
the domain “in-addr.arpa”. Here, the IP addresses are stored in a hierarchical form
such that each level of the tree depicts 8 bits of information of IP address. However,
since domain names have the least significant parts of the name first, but dotted
decimal format has the most significant bytes first, the dotted decimal address is
shown in reverse order. For example, the domain in the domain name system
corresponding to the IP address 171.10.1.2 is 2.1.10.171.in-addr.arpa. The above
mapping is carried out by using a special kind of query called inverse pointer query.