The Internet sometimes breaks pretty easily

Like movie star Steven Seagal, the Internet is “Hard to Kill.” Unfortunately, it’s easy to cripple. You just need a butterfingered network engineer.

That’s what happened Monday when a mistyped computer command disrupted online service for millions of Americans. A similar outage occurred just over a year ago, when an attack by Internet vandals crippled access to many of the world’s most popular websites, including Twitter, Netflix, and Spotify, as well as the Boston Globe.

Incidents like these could make you believe that the Internet is dangerously fragile, and you’d be right. And wrong, as well.

Yes, it’s true that key Internet assets can be taken down by carelessness or malice. But these outages are usually brief and generally affect only small portions of the global network.

“The Internet as a whole is very robust,” said David Clark, senior research scientist at the Massachusetts Institute of Technology, and a key architect of the software protocols that make the Internet work. “The problem is that if you’re in charge of a piece of it, you can always screw your piece up.”

That’s what happened Monday, when someone at a Colorado company called Level 3 Communications pushed the wrong buttons. Recently acquired by CenturyLink Inc., Level 3 runs a massive fiber network that forms a key part of the Internet’s backbone. According to Clark, data from about 36 percent of the world’s Internet addresses travel over the Level 3 backbone to reach their destinations. All of America’s biggest Internet service providers, such as Comcast Corp. and Verizon Communications Inc., have direct connections to Level 3.

So when a Level 3 technician entered an incorrect command at a computer that routes all the traffic, billions of data bits could no longer get where they were supposed to go. Parts of the Internet all over the country temporarily went offline.

This was a foul-up on a massive scale, but similar blunders happen all the time. “There is no day without an incident,” said Andre Robechevsky, technology program manager at the Internet Society, a global group that sets technical standards for the Internet. Many happen outside the United States or involve smaller Internet companies where errors don’t do as much damage.

Robechevsky said that one reason for the occasional glitch is the constant need to reconfigure parts of the Internet. New networks are added, for example, or additional addresses are added to existing networks. Human beings must frequently reconfigure the routing computers, and every reconfiguration is a new opportunity to make a network-crashing mistake.

But such mistakes are usually corrected fast, as Clark said most people in the networking industry know each and immediately reach out when they spot something wrong.

“Internet service providers start calling each other on the phone,” Clark said, “and say, ‘I see something weird. Do you see something weird?’ ” It’s an informal but strong system that ensures that significant problems get fixed fast.

There’s also the inherent decentralization of the Internet. With thousands of service providers, connected to hundreds of backbones, the network tends to break down at different parts. Even when a major portion goes down, people on the other side of the country or the world may not notice a thing.

“It was designed as a robust network, where one network disappearing . . . will not significantly affect the overall operation,” Robechevsky said. In this respect, the Internet on Monday worked just as it was designed to work: The healthy parts stayed healthy.

Still, it’s worrisome that key portions of the global communications network can be knocked out for hours by a few keystrokes. And last year’s far scarier outage was the result of deliberate sabotage by hackers who brought down the data network of Dyn Inc., of Manchester, N.H., whose servers are vital in sending millions of Internet messages to the right addresses. They used an attack method that’s depressingly easy to copy, so there’s every reason to expect similar attacks in the future.

An apocalyptic collapse of the entire US or global Internet is quite unlikely. But that leaves us plenty to worry about. Especially engineers who are great at coding but lousy at typing.