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Configuring a LINUX based NTP Time Server

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Configuring a LINUX based NTP Time Server Powered By Docstoc
					?Computer time synchronisation is highly important in modern computer networks,
precision and time synchronization is critical in many applications, particularly time
sensitive transactions. Just imagine buying an airline seat only to be told at the airport
that the ticket was sold twice because it was purchased afterwards on a computer that
had a slower clock!

Modern computers do have internal clocks called Real Time Clock chips (RTC) that
provide time and date information. These chips are battery backed so that even during
power outages, they can maintain time but personal computers are not designed to be
perfect clocks. Their design has been optimized for mass production and low-cost
rather than maintaining accurate time.

For many applications, this is can be quite adequate, although, quite often machines
need time to be synchronised with other PC's on a network and when computers are
out of sync with each other problems can arise such as sharing network files or in
some environments even fraud!

Network Time Protocol (NTP) is an Internet protocol used for the transfer of accurate
time, providing time information along so that a precise time can be obtained. As NTP
was originally written for LINUX many LINUX based operating systems already
have a version of NTP installed. However the source code is free to download from
the NTP website (ntp.org) the most recent version being v 4.2.4.

NTP (version 4) can maintain time over the public Internet to within 10 milliseconds
(1/100th of a second) and can perform even better over LANs with accuracies of 200
microseconds (1/5000th of a second) under ideal conditions.

NTP works within the TCP/IP suite and relies on UDP, a less complex form of NTP
exists called Simple Network Time Protocol (SNTP) that does not require the storing
of information about previous communications, needed by NTP. It is used in some
devices and applications where high accuracy timing is not as important.

The NTP background program is configured with the file 'ntp.conf'. this may contain a
list of public NTP server references that can be used to synchronise time. NTP time
servers are specified using the 'server' command, any characters after the '#' symbol
are comments:

Example
server time-a.nist.gov # Public NTP server: Maryland
When configured, NTP can be controlled using the commands 'ntpd start' ‘ntpd stop'
‘ ntpq -p' (displays status)

NTP can also authenticate timing resources Note: It is strongly recommends that you
configure a time server with a hardware source rather than from the internet where
there is no authentication. Authentication codes are specified in the 'ntp.keys' file.

Specialist NTP servers are available that can receive transmissions from either GPS or
national time reference broadcasts. They are relatively cheap and the signal is
authenticated providing a secure time reference.

Authentication for NTP has been developed to prevent malicious tampering with
system synchronisation just as firewalls have been developed to protect networks
from attack but as with any system of security it only works if it is utilised.


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; ethernet clocks, GPS time servers, NTP servers, digital wall clocks, atomic
clock servers and SNTP time servers. Please visit us for more information about NTP
products and NTP servers

				
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posted:4/15/2011
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