Today i found out most of our linux machine were not behaving as usual than any other day.
Whenever i tried taking putty of the linux server It used to hang after giving the password .
Later i realize that it was a DNS server issue all across the network .
Also i realize the fact that to avoid ip spoofing linux server validates the client ip/hostname by looking them in dns.As we were having dns issue linux server were not able to resolve the ip/hostname .and was taking time to log in.
However I was able to solve it temporarily by modifying
$ vi /etc/ssh/sshd_config
#service sshd restart.
or by adding client's IP address in Server's /etc/hosts file.