caching DNS

[Stephane Bortzmeyer]

On Mon, Apr 14, 2008 at 01:53:37PM +0300,
 Mohammed Nayeem <nayeem at ksa.zajil.com> wrote 
 a message of 16 lines which said:

> What is the Purpose of Caching DNS normally and how its work which
> they had already Primary & Slave ?

Since it is a very basic question, I suggest to start with a good DNS
tutorial. On dead trees, you have "DNS & BIND" by Liu & Albitz
(O'Reilly editor). On line,
<http://en.wikipedia.org/wiki/Domain_Name_System> is a good start.