Configuration considerations for NTP
Network time synchronization is guaranteed only when a common external time server is used by all switches. If you are in VCS mode, when an ntp server command is invoked on one switch in a cluster, the configuration is applied to all switches in the cluster.
The ntp server command accepts up to five server addresses in IPv4 or IPv6 format. When you configure multiple NTP server addresses, the ntp server command sets the first obtainable address as the active NTP server. If there are no reachable time servers, then the local switch time is the default time until a new active time server is configured.