Then you understand that "shut down the Internet" means 100 percent. Not 80 percent, not 95 percent, not 99 percent. 100 percent.
You just barely get to an immediate 30 percent by "shutting down" about 80 core routers. And then you have at least 5,000 more peering routers to go for that for remaining 70 percent. Minimum. And that's not the end of it.
The following study was the cover story of the Proceedings of the National Academy of Sciences in July 2007.
The core: At the center of the Internet are about 80 core nodes through which most traffic flows. Remove the core, and 70 percent of the other nodes are still able to function through peer-to-peer connections.
The periphery: At the very edge of the Internet are 5,000 or so isolated nodes that are the most dependent upon the core and become cut off if the core is removed or shut down. Yet those nodes within this periphery are able to stay connected because of their peer-to-peer connections.
And from MIT Technology Review regarding the same study:
Take away the core, and an interesting thing happens: about 30 percent of the nodes from the outer shell become completely cut off. But the remaining 70 percent can continue communicating because the middle region has enough peer-connected nodes to bypass the core.
With the core connected, any node is able to communicate with any other node within about four links. "If the core is removed, it takes about seven or eight links," says Carmi. It's a slower trip, but the data still gets there. Carmi believes we should take advantage of these alternate pathways to try to stop the core of the Internet from clogging up. "It can improve the efficiency of the Internet because the core would be less congested," he says.
While routing may still be possible the traffic load would make the links nearly unusable. Also factor in the effect of the remaining routers having to recalculate routes causing a “core meltdown”. Routers become very inefficient when their CPUs are focused on route calculation rather than forwarding packets.
Take a firehose and restrict its flow to a garden hose and you get the idea of what can happen. Data is fluid just like water except when it can’t flow it gets dropped which causes acknowledgment storms, the equivalent of a DDOS attack. Now multiply the effect over millions of nodes.