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1 NTP Configuration
Introduction to NTP
Network time protocol (NTP) is a time synchronization protocol defined in RFC 1305. It is used for time
synchronization between a set of distributed time servers and clients. Carried over UDP, NTP transmits
packets through UDP port 123.
NTP is intended for time synchronization between all devices that have clocks in a network so that the
clocks of all devices can keep consistent. Thus, the devices can provide multiple unified-time-based
applications (See section
Applications of NTP).
A local system running NTP can not only be synchronized by other clock sources, but also serve as a
clock source to synchronize other clocks. Besides, it can synchronize, or be synchronized by other
systems by exchanging NTP messages.
Applications of NTP
As setting the system time manually in a network with many devices leads to a lot of workload and
cannot ensure accuracy, it is unfeasible for an administrator to perform the operation. However, an
administrator can synchronize the clocks of devices in a network with required accuracy by performing
NTP 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 collected
from different devices is meaningful and valid only when network devices that generate the
information 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 that
they adopt the same time.
z When multiple systems cooperate to handle a rather complex transaction, they must adopt the
same time to ensure a correct execution order.
z To perform incremental backup operations between a backup server and a host, you must make
sure they adopt the same time.
NTP has the following advantages:
z Defining the accuracy of clocks by stratum to synchronize the clocks of all devices in a network
quickly
z Supporting access control (See section Configuring Access Control Right) and MD5 encrypted
authentication (See section
Configuring NTP Authentication)
z Sending protocol packets in unicast, multicast, or broadcast mode
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