--8<------ /etc/ntp.conf ----------------------------------------------- ... server 0.centos.pool.ntp.org server 1.centos.pool.ntp.org server 2.centos.pool.ntp.org
... restrict 0.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery restrict 1.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery restrict 2.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery ... --8<--------------------------------------------------------------------
This means roughly : "use these three public NTP servers to synchronize, but don't let them mess with your configuration".
No.
The "server" lines are to tell NTP what servers to query to keep it's own clock in sync. The "restrict" lines are used to limit which ntp clients are allowed to use your server to sync their clock and what alterations (if any) the client can make to your server.