Installing and Administering Internet Services

284 Chapter7

Conﬁguring the Network Time Protocol (NTP)

Getting Started with NTP

Steps to Start NTP Conﬁguration

For your basic NTP conﬁguration, you will need to do the following

Step 1. Choose a source of time.

Step 2. Determine how frequently your system clock should synchronize with

the source of time selected.

Step 3. Select back-up time servers.

Step 4. Conﬁgure your primary NTP server.

The following sections cover these steps in detail.

Choosing the Source of Time

The time of day is ofﬁcially deﬁned, regulated, and distributed by

government organizations. These organizations coordinate with one

another and keep their clocks within nanoseconds of each other at all

times. The ﬁrst step in using NTP is selecting the best source of time for

your organization.

When selecting a source of time, you must be careful to choose the source

of time that will be best for you. Examine them carefully and do not base

your selection on price alone. If the kinds of applications and processes

your network users run are sensitive to time, it is best to select the

source of time that will provide stability and will not be affected by

network delays or outages.

Also, select a source of time that you can reach. The closer the source of

time, the better. Choose a source that is physically close and one that

takes very few network hops to reach. For more information on physical

and network distance, seeXXXX “Conﬁguring Mulltiple Time Servers” on

page 221.

Available Time Sources

The most common time distribution mechanisms used from which you

can draw time are:

• public time server (phone or modem) via the internet

• local clock impersonators

• radio receiver--terrestrial and satellite broadcast