Domain Naming System (DNS)

The mechanism that implements a machine name hierarchy for TCP/IP internet is called Domain Name system (DNS). The two aspects of DNS, one is abstract and other is concrete. Abstract aspect specifies the name syntax and rules for delegation authority over name. And concrete aspect specifies the implementation of it in a computer by mapping names on to addresses. The DNS uses a hierarchical naming scheme known as Domain names.

A domain name consists of a sequence of subnames separated by a delimiter i.e., a dot. For eg : aptechhbl.Yuva.Com. Here each subname is called a label. Any suffix of label in a domain name is called Domain. Therefore in the example, there are three levels of domains i.e., aptechhbl.Yuva.com is the lowest level, Yuva.Com is next higher level and .com is the highest level domain.

A private organization can also establish a domain hierarchy in which the top level and next level labels, may represent various domains of that organization.

Ex : Bir.Vsnl.net.in is a domain name used by one of the new editions. Such domain names are unofficial names.

Most users of the domain technology follow the hierarchical labels used by the official. Internet domain system, because it scheme is flexible and comprehensive. The domain names allotted by Internet Authority are official names- Internet has choosen many top level names that refer various organization and institutions.

Domain Name

Meaning

com Commercial Organisation

edu Educational Institutions

gov Government Organization

mil Military group

net Major network support centers

org Other organizations

ARPA Arpanet domain

int International organization

Country code Each country

Domain Name Resolution

The conceptual domain name scheme as a tree is easy to understand but it does not provide several details. An algorithm can be used to overcome the drawback i.e., Name, resolution algorithm. The domain name resolution proceeds top down, starting with root server and coming down to name servers. The domain name system can be used in two ways for resolution.

(a) Contacting name servers one at a time for resolution i.e., interactive resolution.
(b) Asking the name server or complete translation i.e., recursive resolution.

In either case first a client forms a querry containing the items, such as name to be resolved, declaration of the class of name, type of answer desired and a code for translation. Then it sends to a name server for resolution. Upon receiving query domain name server checks to see if the name lies in the subdomain if it is found it translates the name to an address and appends an answer to be query to send it back to client.

The cost of lookup for the names in servers in very high. Therefore the servers use cache memory to speed up the operation and as well to save the cost.

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