The internet protocol NTP or the network time protocol is primarily designed and developed in a way to synchronize network time clients to an accurate reference clock. There are number of algorithms defined by the NTP and some specific message structure in order to pass accurate timing information from a server reference to a client machine. There is different way to install the freely available public NTP server software distribution. The article also shows how to configure NTP to synchronize time with an internet based public time reference.

The Internet based NTP servers are divided in two different categories such as primary and secondary servers. The primary servers are used to provide precise time and for this it used highly accurate external timing reference such as GPS or radio clocks. The secondary reference servers provide slightly reduced accuracy as they synchronize their time with the primary reference servers. The primary reference servers are also designated as stratum 1 where as the secondary servers are designated as stratum2.

Users can download freely the NTP source code under the GNU public license from the NTP website at ‘ntp.org’. It was originally developed for the Linux operating system. As soon as the source code is obtained it should be installed and compiled and configured on the host computer. With the installation of the source code it is automated and configuration scripts supplied in the distribution. Inmost of the Linux based operating systems the NTP package is pre-installed. But it would be better to down load the latest version.

The NTP daemon is configured by a configuration file ‘ntp.conf’ which may contain a list of public NTP server references. These references can be used by the host to synchronize time. To specify public NTP time references the ‘server’ command can be used where the characters specified after the # symbol are comments-

Server time-a.nist.gov # Public NTP server: NIST, Gaithersburg, Maryland server time-c.timefreq.bldrdoc.gov # Public NTP Server: NIST, Boulder, Colorado
After the configuration file is complete the NTP daemon can be started using the ‘ntpd start’ script. There are also some other scripts available to control the daemon such as ‘ntpd stop’ and ‘ntpd restart’. The current synchronization status of the daemon can be shown through a query ‘ntpq-p’. To control the access permissions to the NTP server ‘restrict’ command can be used.

There is some additional security level the NTP server provides by means of some authentication codes. The authentication codes are specified in the file ‘ntp.keys’ that are specified using key reference, encryption code and authentication key.