AUDIE CORNISH, HOST:

North Korea, meanwhile, experienced another nationwide Internet outage today. It lasted for about half an hour. This followed a blackout that went on for some nine hours yesterday and raised a lot of questions about who or what could be behind the disruption. Dyn Research has been watching the outages. The firm studies internet performance around the world. And Doug Madory, Dyn's director of Internet analysis, was among the first people to flag what was happening. Welcome to the program, Doug.

DOUG MADORY: Hello.

CORNISH: So when did you first notice? What exactly did you see?

MADORY: So we monitor - one of our data sources that we use is BGP - that's Border Gateway Protocol. And what that is is just the information that the Internet service providers around the world exchange with each other on how to direct traffic around the Internet from one place to another. And so the BGP routes for North Korea starting on Sunday started to become very unstable. We saw them go down, come right back up, go down, come right back up, and was having a lot of difficulty staying online.

CORNISH: Help us understand in layman's terms, like, what happened. I don't know how common it is for North Korea to have outages.

MADORY: Sure. In the last couple of years, there's been occasions that they have had outages. And because they are the only party that handles international connectivity for North Korea, when they have an outage then essentially they have a national outage on this very small Internet they have. So what we saw in the last couple of days was not something that I've observed before. Typically the outages are brief. They are also isolated events. And we don't see this 24 hours of routing instability where they are struggling to maintain a connection followed by nine and a half hours of blackout.

CORNISH: How large is the network of North Korea? I mean, give us some comparison.

MADORY: Absolutely. It's a little over a thousand IP addresses for the country. As comparison, the Internet - the United States is just under a billion, and so it is quite small.

CORNISH: It's not unusual to see Internet outages in many places in the world, right? I mean, give us some examples of other instances where governments experience Internet outages. Why - you know, how does this compare?

MADORY: OK. Sure. There have been a number of cases in the last couple of years, either by the direction of the government - that included Syria, Egypt and then last year was Sudan - and then even in cases of antigovernment protestors or forces in Thailand and Libya. North Korea, like Cuba and Uzbekistan and a handful of countries that rely on a single ISP for their international connectivity, they have an outage then that means they are shut off from the global Internet.

CORNISH: What do you make of the speculation that the U.S. is somehow responsible for this outage?

MADORY: I think this doesn't look like an outage as far as like a fiber cut or a power outage - some of the more catastrophic technological failures that cause Internet outages. Like I said, we saw these networks struggling to maintain connections for hours and hours until finally they dropped offline. And so that's more consistent with two possibilities - benign explanation would be that this is just extraordinarily poor timing for a software glitch on the router or this is also consistent with some sort of a denial of service attack directed at the network of North Korea. Given the sophistication was quite low, it does seem that if it were a cyber-attack that it would be surprising to find out a nation-state did this and it took them hours to take down this tiny network.

CORNISH: Doug Madory - he's the director of Internet analysis for Dyn Research. He joined us to talk about the Internet blackouts North Korea has been experiencing over the last 24 hours. Thanks so much for explaining it to us.

MADORY: Thank you. Transcript provided by NPR, Copyright NPR.