2.2.1.3 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.

Note: This recommendation only applies if ntp is in use on the system.

Rationale:

If ntp is in use on the system proper configuration is vital to ensuring time synchronization is working properly.

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>

Add or edit the OPTIONS in /etc/sysconfig/ntpd to include '-u ntp:ntp':

OPTIONS='-u ntp:ntp'

Reload the systemd daemon:

systemctl daemon-reload

Enable and start the ntp service:

systemctl --now enable ntpd

See Also

https://workbench.cisecurity.org/files/3636