Distribution of DNS
1.By centralized data base
The information contained in the domain name space must be stored. A simple design or DNS would have one DNS server that contains all the mappings. In this centralized design. Client simply direct all queries to the single DNS server, and the DNS server responds directly to the querying clients. The problems with a centralized design include.
a.Traffic Volume: A single DNS server would have handle all DNS queries (for all the HTTP request and e mail message generated from hundreds of millions of hosts.
b. A single point of failure. It the DNS server crashes so does the entire internet.
c. Distant Centralized Database: A single DNS server cannot be close to all querying client. If we put the single DNs server in new York city then all quarters form Australia must travel to the other side of the globe perhaps over slow and congested links. This can lead to significant delays.
d.aintenance: This single DNS server would have to keep records for all internet hosts. Not only would this centralized database be huge,, but it would have to be updated frequently to account for every new host to those servers. In the internet there are 13 root DNS serves ( Ladled a through M) most of which are located in north America.
In summary single DNS with centralized data base has lot of problems. To overcome these problems DNS should b presented in a particular hierarchy. Show as below.