3Com 4200G 12-Port, Руководство по настройке

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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 is based on user datagram protocol (UDP).
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 network 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 negotiate with
other network devices by exchanging NTP packet to reach the time for them to
synchronize to.
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
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 with the
increasing of stratum number. The clocks with the stratum of 16 are in
unsynchronized state and cannot serve as reference clocks.
The local clock of an S4200G series switch cannot operate as a reference clock. And
an S4200G series switch can serve as a time server only when it is synchronized.