When Time Servers go Bad
“Time is what prevents everything from happening at once,’ said eminent physicist John Wheeler. And when it comes to computers his words couldn’t be any more relevant.
Timestamps are the only method that a computer has to establish if an event has occurred, is meant to occur or shouldn’t be occurring just yet. For a home PC, the computer relies on the inbuilt clock that displays the time on the corner of your operating system, and for most home uses this is satisfactory enough.
However for computer networks that have to communicate with each other, relying in individual system clocks can cause untold problems:
All clocks drift, and computer clocks are no different and problems occur when two machines are drifting at different rates as the time does not match up. This poses a conundrum for a computer as it is unsure of which time to believe and time critical events can fail to occur and even simple tasks like sending an email can cause time confusion on a network.
For these reasons, time servers are commonly used to receive the time from an external source and distribute it around the network. Most of these devices use the protocol NTP (Network Time Protocol) which is designed to provide a method of synchronising time on a network.
However, time servers are only as good as the time source that they rely on and when there is a problem with that source, synchronisation will fail and the problems mentioned above can occur.
The most common cause for time server failure or inaccuracy is the reliance on internet based sources of time. These can neither be authenticated by NTP nor guaranteed to be accurate and they can also lead to security issues with firewall intrusion and other malicious attacks.
Ensuring the NTP time server continues to get a source of highly accurate time is fairly straight forward and is all a matter of choosing an accurate, reliable and secure time source.
In most parts of the world there are two methods that can provide a secure and reliable source of time:
- GPS time signals
- Radio referenced time signals
GPS signals are available anywhere on the planet and are based on GPS time which is generated by atomic clocks onboard the satellites.
Radio referenced signals like MSF and WWVB are broadcast on long wave from physics laboratories like NIST and NPL.
