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How to Build a NTP Server

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					NTP, or Network Time Protocol, is a standard Internet protocol used to distribute
accurate time to client computers. NTP is freely downloadable from the NTP website.
With the addition of an accurate reference clock, you can build your own highly
accurate stratum one NTP Server.

This article describes how to build and configure your very own stratum one NTP
Server. By adding a low-cost GPS or radio time reference to your Linux machine, you
can have your very own highly accurate time reference. Your NTP server can be used
to synchronize all the machines on your network to the precise time.

NTP is available as source code for compilation and configuration on a Linux
machine. The source code freely downloadable from the NTP.org website. Many
Linux distributions, such as Redhat and Debian have a pre-installed version of NTP.
Other distributions may include it as an installable RPM.

In order to build a stratum one NTP server, you need an accurate external timing
reference. Many timing references are available, most utilise GPS or national time and
frequency radio sources such as WWVB, DCF77 and MSF. The Global Positioning
System (GPS) is a great timing reference, since it is available worldwide and the
equipment required for receiving time and positioning information is very low-cost.

Most GPS receivers have a RS232 serial port that can be easily interfaced to a PC.
The receiver generally provides continuous time and positioning information in a
standard format known as NMEA. An NTP server can utilise the timing information
provided by a NMEA receiver as an accurate timing reference. Additionally, some
receivers also provide a highly accurate pulse output that can be utilised by a NTP
server as a highly precise epoch. Any timing pulse generated by a GPS receiver may
need to be converted into a usable RS232 signal level. This can be achieved by
feeding the pulse into a RS232 driver chip.

Many radio based reference clocks are available that utilise national time and
frequency standards. WWVB is a US radio time and frequency transmission, DCF77
is transmitted from Germany, MSF is available throughout the UK. The advantage of
a radio signal as a reference clock for your NTP server is that you can usually pick up
a good signal indoors, close to the NTP server. In contrast, GPS requires an antenna
with a good view of the sky.

Once you have your NTP server external reference clock set-up and installed, you
need to configure the clock in the NTP configuration file 'ntp.conf'. This usually
involves finding and specifying the reference clock code for your timing reference.
Once configured, your NTP server will act as an accurate source of time for your
network time clients.

Most modern computers operating systems can utilise NTP to synchronize time.
Linux and Unix machines can utilise the NTP distribution itself. Modern Windows
operating systems such as XP and 2003 have pre-installed SNTP clients that can point
to the IP address or DNS name of a NTP server for synchronisation. Many network
devices such as routers and switches can also utilise your NTP server for
synchronization.

				
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