3Com Switch 7754, Configuration Manual

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NTP C
ONFIGURATION
Introduction to NTP
Network time protocol (NTP) is a time synchronization protocol defined by
RFC1305. It is used for time synchronization among a set of distributed time
servers and clients. NTP transmits packets through UDP port 123.
NTP is intended for time synchronization of all devices that have clocks in a
network, so that the clocks of all devices can keep consistent. This enables the
applications that require unified time.
A system running NTP not only can be synchronized by other clock sources, but
also can serve as a clock source to synchronize other clocks. Besides, it can
synchronize, or be synchronized by other systems by exchanging NTP packets.
Applications of NTP NTP is mainly applied to synchronizing the clocks of all the network 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 accounting system requires that the clocks of all the network devices be
consistent.
■
Some functions, such as restarting all the network devices in a network
simultaneously require that they adopt the same time.
■
When multiple systems cooperate to handle a rather complex event, to ensure
a correct execution order, they must adopt the same time.
■
To perform incremental backup operations between a backup server and a
host, you must make sure they adopt the same time.
As setting the system time manually in a network with many devices leads to a lot
of workload and cannot ensure the accuracy, it is unfeasible for an administrator
to perform the operation. However, an administrator can synchronize the devices
in a network with required accuracy by performing NTP configuration.
NTP benefits from the following advantages:
■
Defining the accuracy of clocks by strata to synchronize the time of all the
devices in a network quickly
■
Supporting access control and MD5 authentication
■
Sending protocol packets in unicast, multicast or broadcast mode
n
The accuracy of a clock is determined by its stratum, which ranges from 1 to 16.
The stratum of the reference clock ranges from 1 to 15. The accuracy descends