NTP Server

On server

# yum install ntp
# chkconfig ntpd on
# vi /etc/ntp.conf
add a line
restrict default ignore
restrict 202.54.1.5 mask 255.255.255.245
server 202.54.1.5
(Replace 202.54.1.5 and mask with actual remote ISP or ntp.org NTP server IP. Save and close the file.)
then client configuration
#vi /etc/ntp.conf
add a line like
server <NTP server IP>
restrict <server IP>mask <subnet mask>
#iptables -F
#ntpdate -b <server IP>

Now all is done