>>>>> "saravanan" == saravanan ganapathy writes:

saravanan> But why slave servers send a notification? To whom it will send?

Because RFC1996 says so. Please read it. I quote:

2. Definitions and Invariants

....

Notify Set set of servers to be notified of changes to some
zone. Default is all servers named in the NS RRset,
except for any server also named in the SOA MNAME.
Some implementations will permit the name server
administrator to override this set or add elements to
it (such as, for example, stealth servers).