DNS By: Muhammad Hanif

Quote of the day……. Anger corrupts faith in the same way as vinegar destroys honey. Make somebody happy today, and mind your own business.

DNS (Domain Name System) DNS stands for Domain Name System To identify an entity, TCP/IP protocols use the IP address, which uniquely identifies the connection of a host to the Internet. However, people prefer to use names instead of numeric addresses. Therefore, we need a system that can map a name to an address or an address to a name.

DNS Users generally prefer names to numbers Computers prefer numbers to names DNS provides the mapping between the name and numbers i.e. domain name to IP address

DNS In the Internet the domain name space is divided into the Following sections: Generic Domains Country Domains

Generic Domain The generic domains define registered hosts according to their generic behavior.

Country Domain The country domains section uses two-character country abbreviations e.g., pk for Pakistan

Name System Each name is made of several parts separated by dot (.) The first part can define the name of an organization. The second part can define the nature of the organization. i.e. commercial, education, organization etc. Some domain names have other parts like the starting parts will define departments in the organization & the ending parts will specify the country or sub type of organization. E.g. www.yahoo.com www.uoslahore.edu.pk For each new domain registartion, first it is check that some one else don’t has domain name, if not then it is registered.

Domain Name Space For simplicity the domain name is design hierarchal as shown in figure.

Resolution Mapping a name to an address or an address to a name is called name-address resolution. Resolver: DNS is designed as a client-server application. A host that needs to map an address to a name or a name to an address calls a DNS client called a resolver. The resolver accesses the closest DNS server with a mapping request. If the server has the information, it satisfies the resolver; otherwise, it refers the resolver to other servers to provide the information. After the resolver receives the mapping, it finally delivers the result to the process that requested it.