NTP synchronizes the time of day among a set of distributed time servers and clients in order to correlate events when receiving system logs and other time-specific events from multiple network devices. NTP uses the User Datagram Protocol (UDP) as its transport protocol.

All NTP communications use Coordinated Universal Time (UTC). An NTP server usually receives its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server, and then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of each other.

NTP uses a stratum to describe the distance between a network device and an authoritative time source:
  • A stratum 1 time server is directly attached to an authoritative time source (such as a radio or atomic clock or a GPS time source).

  • A stratum 2 NTP server receives its time through NTP from a stratum 1 time server.

Before synchronizing, NTP compares the time reported by several network devices and does not synchronize with one that is significantly different, even if it is a stratum 1.

You an use the security features of NTP to avoid the accidental or malicious setting of incorrect time. One such mechanism is available: an encrypted authentication mechanism.

Though similar, the NTP algorithm is more complex and accurate than the Simple Network Time Protocol (SNTP).


Enabling this feature results in synchronizing the system clock; therefore, it may affect all sub-systems that rely on system time.