I just finished a really cool project for my CS Theory class. We were given the information about how the various Autonomous Systems on the Internet were connected for 1997, 1999, 2002, and 2004. The assignment was to find things like what the average number of connections (called degree) nodes had with each other, what the largest number of hops between 2 nodes could be (Called the diameter), average distances, etc.

The cool part was when we investigated how the system reacts to failure of nodes. I have attached the reports here:

http://www.msblabs.org/as-attack/report-100.txt
http://www.msblabs.org/as-attack/report-500.txt

Basically, here is what these reports say:

If 100 or even 500 random nodes failed all at the same time, over 99.5% of the nodes stay connected in 1 mass, and can still talk to each other. If the largest nodes were deliberately attacked and removed, the shit hit the fan.

When 100 ASes are attacked and removed, only 55% of the nodes remained in 1 mass, and the average distances between any 2 nodes as well as the max distance inside the mass doubled. Now only half the internet is reachable (if you were lucky), while the speed tanks and the bottlenecks double.

When 500 ASes are attacked and removed, the Internet fractures into an unusable mess. Over 11000 little "islands" of 1 or two nodes are created (remember there were only ~17000 nodes to begin with!). The largest single mass only has 1388 nodes. Only 8% of the Internet is reachable, if you are luckily enough to be in that mass. The speed is now 1/5 of what it was as the average number of hops jumps from 3.7 to over 21.

I'm going to do some more reseach on AS systems and how protected they are, but I think I understand what Mike meant about the Internet being taken out without poisoning the DNS trees.