1-11 NTP ConfigurationWhen configuring NTP, go to these sections for information you are interested in:z Introduction to NTPz NTP Configuration Task Listz Configuring NTP Implementation Modesz Configuring Access Control Rightz Configuring NTP Authenticationz Configuring Optional NTP Parametersz Displaying NTP Configurationz Configuration ExamplesIntroduction to NTPNetwork Time Protocol (NTP) is a time synchronization protocol defined in RFC 1305. It is used for timesynchronization between a set of distributed time servers and clients. Carried over UDP, NTP transmitspackets through UDP port 123.NTP is intended for time synchronization between all devices that have clocks in a network so that theclocks of all devices can keep consistent. Thus, the devices can provide multiple unified-time-basedapplications (see section Applications of NTP).A local system running NTP can not only be synchronized by other clock sources, but also serve as aclock source to synchronize other clocks. Besides, it can synchronize, or be synchronized by othersystems by exchanging NTP messages.Applications of NTPAs setting the system time manually in a network with many devices leads to a lot of workload andcannot ensure accuracy, it is unfeasible for an administrator to perform the operation. However, anadministrator can synchronize the clocks of devices in a network with required accuracy by performingNTP configuration.NTP is mainly applied to synchronizing the clocks of all devices in a network. For example:z In network management, the analysis of the log information and debugging information collectedfrom different devices is meaningful and valid only when network devices that generate theinformation adopts the same time.z The billing system requires that the clocks of all network devices be consistent.z Some functions, such as restarting all network devices in a network simultaneously require thatthey adopt the same time.z When multiple systems cooperate to handle a rather complex transaction, they must adopt thesame time to ensure a correct execution order.
