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.