Undersea cables

Who is most - and least - vulnerable to cable clipping?

I’m a researcher at the UC Berkeley Center for Long-Term Cybersecurity where I direct the Daylight Lab. This newsletter is my work as I do it: more than half-baked, less than peer-reviewed.

98% of traffic on the Internet travels through cables that run deep under the ocean. These cables are the physical material through which data flows through terrestrial space. (Check out Cleo Abram’s videos on TikTok).

Cutting the cable

Various people, particularly the US military, have been concerned about cable clipping. The idea is that someone—a foreign navy or, in Canada, beavers—would come around and snip a submarine Internet cable.

A well-aimed cable clip could cause extreme disruption. Outages, congestion; locally, regionally, sometimes globally.

My questions: which country’s Internet is most vulnerable to this type of cable clipping event? Which country is least susceptible? As you’ll see, the answers to these questions reflect political relationships—internationally and domestically. Moreover, as world powers like China build new cables, these questions will likely shape geopolitics in the future.

A network of the network

I constructed a graph—effectively, a network of cable connectivity between countries. (Find all code and data here). I used network analysis methods to identify points of fragility and strength in this network.

Where’s the power?

Who’s the hardest to disconnect? That’s isn’t just a question of how many people you connect to—it’s a question of how vital those connections are. For example, India could sever its links to Sri Lanka, but doing so would cut off its most direct path to Africa! 1

I used a measure called betweenness centrality, which captures how frequently nodes function as intermediaries (or brokers) for other nodes. This measure serves as a proxy for each country’s “leverage” over the global network. It answers the question, “how much trouble could each country cause by cutting all of the undersea cables within their borders?”

So, who has the most leverage over the global Internet?

Long-time readers of this blog will be unsurprised to learn that the US has incredible leverage over the global network of submarine Internet cables. (Look back at the network graph above—you can see the US's brokerage position between Europe and Asia).2

The upshot: most countries likely couldn’t afford to cut cables bound for the US. The consequences for the rest of the world—and them—would be unbearable.

Checking the hype: Is the PEACE Cable really a threat?

Given the US’s high-leverage position, I’m not surprised that countries like China are doing some cable diplomacy, laying the so-called PEACE Cable to Europe. I’m also unsurprised that the US is upset about it. A new link between Europe and Asia threatens to weaken their brokerage power. From the Bloomberg article above:

In 2018, Australia scuppered a Huawei Marine Networks cable that would have connected the Solomon Islands, Papua New Guinea, and Sydney via a group of Pacific island nations. Last year, a portion of an 8,000-mile cable from Los Angeles to Hong Kong, partly funded by Google and Facebook, was rerouted after U.S. national security officials blocked plans for a connection to territory that’s under Chinese control.

So that’s the narrative: China’s power over the physical layer of the Internet is growing. Let’s check this narrative against some data. What does the future really bear for the US’s power over the physical layer of the Internet?

As in the application layer, power over the Internet continues to consolidate in the US.

I analyzed the current network graph against the probable future network, considering all cables under construction but not yet operational. Once all planned lines come online, the US’s betweenness centrality will increase 4.5% over the next two years. Meanwhile, China’s will decrease by 15%!

Does the PEACE Cable alone threaten the US’s leverage? Maybe. But in the context of all planned cables, the story is quite different. As in the application layer, power over the Internet continues to consolidate in the US.

What now?

Three things:

  1. Identify weak points. Where is the Internet most vulnerable to outages—and what links would make those places more resilient?

  2. Appreciate the political significance of new cable lines. For example, how do new submarine cables change the balance of geopolitical influence over the network?

  3. Understand connectivity within countries. This data is between countries. Terrestrial cable data will help us understand patterns within national borders—for example, urban/rural divides.

1. Identify weak points

Who risks having their Internet cut off entirely by a foreign power? A few nations connect to only one other country via undersea cable.3

  • Saint Pierre and Miquelon only connects to Canada

  • Vanuatu and Tonga only connect to Fiji

  • Ukraine only connects to the Russian Federation (see Limonier et al., 2021).

These relationships reflect historical relationships of power and dependency. And, as emerging powers build new cables (e.g., connecting China and Europe), these patterns will go on to shape geopolitical relations in a rapidly-changing world.

Who risks having their Internet cut off entirely by a foreign power? A few nations connect to only one other country.

I’m worried for Ukraine—and for Tonga. Once we get data on terrestrial cables, I’m sure I’ll be worried for Kashmir and Rojava. These measurements can help us learn who needs some additional leverage on the network—and what they can do to help themselves get it.4

2. Appreciate the political significance of new cable lines

The Internet both shapes and reflects geopolitics. The connectivity patterns we see in undersea cables are, to a degree, the function of historical relationships. But the Internet shapes politics as well. It’s of strategic importance to every country in the world.

An ongoing interest of mine is using Internet measurement to track geopolitical shifts. By watching our network change, we can quantify who is losing or gaining influence. And, watching connectivity patterns change between particular countries could help us understand how geopolitical relationships are shifting, weakening, or strengthening over time.

3. Understand connectivity within countries

Here’s the big thorn in my side: I don’t have data on cables that transport data over the land. If you know of a good source for terrestrial cable data, please let me know.

Why land cables? Here’s a question: which city do you think would be easier to disconnect from the global Internet: San Francisco or Natchitoches, Louisiana?

Internet infrastructure reflects and shapes domestic power dynamics—for example, the dependencies of rural areas on urban centers. How does Internet infrastructure intersect with rurality/urbanity in the US and abroad? What does that intersection mean for people’s access to services (like telemedicine)?

I look forward to digging more here.

This work was supported in part by the Internet Society.

In other news… Op-ed in The Hill, topical content

I wrote an op-ed in The Hill about my ongoing concern with caching services (CDNs, reverse proxies) and how they threaten to break the dang Internet.

In the op-ed, I mentioned the US’s no-due-process domain seizures. Well, speak of the devil, the US just seized the domains of some Iranian news outlets. This is the first instance I’m aware of in which the US has flexed its jurisdictional muscles over top-level domain registrars to cut down on “disinformation.” (In the past, the US used domain seizures primarily for copyright claims). This is an escalation for sure.

Again, the unique thing about the US’s web-blocking strategy is that it doesn’t technically fragment the Internet: when China blocks something, it’s blocked in China; when the US block something, it’s blocked for the whole world. That said, this kind of blocking does risk making the US an (even) less ‘benign’ hegemon. Watch this space!


I always thought the focus on cable clipping was a bit odd. A country can use its army to cut off cables domestically. Imagine if China “turned off” cables bound for Indonesia on their won switchboard. Indonesia would feel it!


We do have a few surprises here, though. Fiji's betweeness centrality is high; it connects the South Pacific (including Australia and New Zealand) to ‘the West.’ And two countries (Tonga and Vanuatu) are utterly reliant on it. (A prior version of this post claimed Fiji had leverage over Australia—as Doug Madory points out, that’s not quite right).


Once we get terrestrial cables, this picture will become a bit clearer. For example, Ukraine has a terrestrial connection to Western Europe through the C&W East cable.


Before anyone emails me about Starlink: yeah, okay, maybe someday companies like Astranis will provide a satellite-powered link to the global Internet. But I understand that these satellite connections are nowhere near ready to transport data at the volumes of undersea cables. That will require some future technology, potentially involving quantum entanglement.

Okay, I can’t just leave you hanging on that. Here’s the idea. You entangle two particles. One stays on Earth, and one goes up to a satellite. When you spin the particle on earth, the particle on the satellite spins the same way simultaneously. You’ve got faster-than-light communication that’s completely tamper-resistant!

(Remember: if an eavesdropper snuck into your facility and secretly entangled a particle of their own, they wouldn’t be able to observe its state without disturbing it—and the other entangled particles in so doing).

China’s Micius experiment is a working proof of concept for this idea.