Ensure ntp is configured - restrict -4

Information

ntp is a daemon which implements the Network Time Protocol (NTP). It is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on NTP can be found at http://www.ntp.org. ntp can be configured to be a client and/or a server.

Solution

Add or edit restrict lines in /etc/ntp.conf to match the following:
restrict -4 default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery

Add or edit server or pool lines to /etc/ntp.conf as appropriate:
server <remote-server>

Configure ntp to run as the ntp user by adding or editing one of the following files as appropriate for your distribution:
/etc/sysconfig/ntpd :
OPTIONS="-u ntp:ntp"

/etc/sysconfig/ntp :
NTPD_OPTIONS="-u ntp:ntp"

/etc/init.d/ntp:
RUNASUSER=ntp

See Also

https://www.cisco.com/c/en/us/td/docs/security/firepower/623/configuration/guide/fpmc-config-guide-v623.html