Installing Network Time Protocol (NTP) is optional but strongly recommended. NTP helps ensure a consistent time of day across all of the service nodes in the cloud. If you enable NTP in a network, configure the service nodes to obtain their time over the network.
If IP multicast is enabled on the IP subnets on which the service nodes reside, you can leverage IP multicast to configure NTP.
If IP multicast is not enabled on the IP subnets on which the service nodes reside, configure NTP manually.
Using NTP involves configuring the NTP server and the NTP client. Typically, the NTP server is a separate system from the other systems on which you configure OpenStack. The NTP client is installed and configured on the nodes or systems that host the OpenStack components.
For more information about NTP, refer to the documentation at http://www.ntp.org/documentation.html.