3Com Switch 7750 Configuration Guide Guide

NTP CONFIGURATION

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

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