3Com Switch 4210 9-Port, Руководство по настройке

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NTP C
ONFIGURATION
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 “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:
■
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.
■
The billing system requires that the clocks of all network devices be consistent.
■
Some functions, such as restarting all network devices in a network
simultaneously require that they adopt the same time.
■
When multiple systems cooperate to handle a rather complex transaction, they
must adopt the same time to ensure a correct execution order.
■
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:
■
Defining the accuracy of clocks by stratum to synchronize the clocks of all
devices in a network quickly
■
Supporting access control (See “Configuring Access Control Right” ) and MD5
encrypted authentication (See “Configuring NTP Authentication” )
■
Sending protocol packets in unicast, multicast, or broadcast mode
n
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The clock stratum determines the accuracy, which ranges from 1 to 16. The
stratum of a reference clock ranges from 1 to 15. The clock accuracy decreases