Network time Protocol (NTP) is used as a synchronisation tool by most computer networks. NTP distributes a single time source around a network and ensures all devices are running in synchronisation with it. NTP is highly accurate and able to keep all machines on a network to within a few milliseconds of the time source. However, where this time source comes from can lead to problems in time synchronisation within a network.
Time is an essential aspect to computer network security. It is time that all machines on a network rely on to conduct applications and processes. Time is the only reference a computer has to know when to do something or acknowledge when a process has already happened. When time is out of sync this can lead to all sorts of errors, and furthermore, unsynchronised time exposes a network vulnerability that malicious users can exploit.
Computer network time doesn’t only have to be synchronised within a network, but also should be synchronised with any client of peer machines with which the network communicates. This is because any discrepancies could lead to the same errors that lack of synchronisation causes within a network, as essentially, when a computer communicates with another network, the client temporarily becomes part of the host’s network.
Many computer networks achieve this synchronisation using an online source of UTC (Coordinated Universal Time). UTC is the same everywhere in the world, allowing computers in different time zones to communicate with the same timescale.
The problem with using the internet for a source of time is that the accuracy of these level 2 time servers can’t be authenticated, Because computers require highly accurate, the distance between a client and the time source can lead to big discrepancies. Furthermore, not all online time sources are regularly checked for accuracy.
Another big problem with online time sources is that by utilising them, a computer network is leaving a gap in its firewall that could be exploited by malicious software.
NTP Time Servers
A more secure and more accurate solution is to get the time directly from an atomic clock source. Because atomic clocks are accurate to within a millionth of a second, the network time will always be accurate. External atomic clock sources are also more secure as malicious software in unable to exploit the signals.
Receiving a source of atomic clock time requires the use of an external NTP time servers that can receive signals from either the GPS network or one of the radio signals broadcast by the big physics laboratories such as NIST and NPL.