Beware the NTP “false-ticker” – or do the time warp again…

For the uninitiated, it’s easy to keep the clocks of computers on the Internet in synch using a protocol called NTP (Network Time Protocol).

Why might you want to do this? It’s very helpful in a large network to know that all your gear is synchronised to the same time, so that things such as transactional and logging information has the correct timestamps. It’s a must have for when you’re debugging and trying to get to the bottom of a problem.

There was an incident earlier this week where the two open NTP servers run by the US Naval Observatory (the “authority” for time within the US) both managed to give out incorrect time – there are reports of computers which synchronised against these (and more importantly, only these, or one or two other systems) had their clocks reset to 2000. The error then corrected, and clocks got put back.

Because the affected systems were chiming either only against the affected master clocks, or a limited number of others, the two incorrect times, but from a high stratum source, were taken as being correct and the affected systems had their local clocks reset.

There’s been discussion about the incident on the NANOG list…

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