NTP Servers: Basic NTP Configuration
This article explores the basics of NTP configuration.
Network Time Protocol
has been developed to keep computers synchronized. All computers are prone to
drift and accurate timing is essential for many time critical applications.
A version of NTP is
installed on most versions of Windows (although a stripped down version called
SNTP ?Simplified NTP- is in older versions) and Linux but is free to download
from NTP.org.
When synchronising a
a network it is preferable to use a dedicated NTP server that receives a timing
source from an atomic clock either via specialist radio transmissions or the
GPS network. However, many Internet time references are available, some more
reliable than others, although it must be noted Internet based time sources can’t
be authenticated by NTP, leaving your computer vulnerable to threats.
NTP is hierarchical and
arranged into stratum. Stratum 0 is timing reference, while stratum 1 is a
server connected to a stratum 0 timing source and a stratum 2 is a computer (or
device) attached to a stratum 1 server.
The Basic
configuration of NTP is done using the /etc/ntp.conf file you have to edit it
and place the IP address of stratum 1 and stratum 2 servers. Here is an example
of a basic ntp.conf file:
server xxx.yyy.zzz.aaa prefer (time server address
such as time.windows.com)
server 123.123.1.0
server 122.123.1.0
stratum 3
Driftfile /etc/ntp/drift
The most basic
ntp.conf file will list 2 servers , one that it wishes to synchronise too and an
IP address for itself. It is good housekeeping to have more than one server for
reference in case one goes down.
A server with the tag
?prefer’ is used for a trusted source ensuring NTP will always use that server
when possible. The IP address will be used in case of problems when NTP will
synchonise with itself is. The drift file is where NTP builds a record of the system
clock’s drift rate and automatically adjusts for it.
NTP will adjust your
system time but only slowly. NTP will await at least ten packets of information
before trusting the time source. To test NTP simply change your system clock by
half an hour at the end of the day and the time in the morning should be
correct.
About the author
Richard N Williams is a technical author and a
specialist in the telecommunications and network time synchronisation industry
helping to develop dedicated time server products. Please visit us for
more information about a GPS time server or other NTP server
