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‘Leap second’ confuses some Web routers

Glitch causes about 2,000 networks to crash, most only briefly

Routers and switches such as those in this data center in Council Bluffs, Iowa, allow such centers to talk to each other. Connie Zhou/Google via Associated Press

Sometimes, the littlest changes have big effects. This week, a “leap second” — a periodic one-second adjustment that keeps the world’s official clock in time with the Earth’s rotation — caused intermittent outages to more than 2,000 Internet networks around the globe.

Dyn Inc., a Manchester, N.H., company that monitors Internet performance, reported the outages occurred just after midnight Tuesday, around the time the extra second was added. Generally, when service outages are reported, it’s the fault of a single Internet service provider, or ISP. In this case, because the outages were so widespread, Dyn concluded that the time change was the most likely reason.

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“It seems like a couple of different types of routers couldn’t handle that, and their software crashed,” said Doug Madory, Dyn’s director of Internet analysis. Madory said software engineers were discussing the problem on forums across the Web and found that the crash most likely occurred because of rusty software in routers.

Most networks were back online within a few minutes, although others took a few hours to reset themselves. Madory said that the fix was simple: Restart the router, a device that finds the fastest route to connect a computer to the Internet.

Leap seconds are fairly unusual, with only 26 implemented since 1972. That means potential outages are hard to prepare for, since it’s difficult to know what a system can handle in such an unlikely scenario. Madory said some engineers recommend inserting a leap second every couple of months, so they can test whether their software can handle it.

It doesn’t seem as if this latest outage has had any verifiable lasting consequences. The number of router networks affected, 2,096, is only a fraction of one percent of the total worldwide.

“Most models survived this with no issue,” Madory said. “By the numbers, this wasn’t a global catastrophe.”


Eden Shulman can be reached
at eden.shulman@globe.com.

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