Herculean Internet and Web Have Achilles' Heels

by John Roach

The Internet and World Wide Web are communications networks that have unleashed unprecedented wealth and connectivity to millions of people around the world. But a well-planned attack could bring these kings of the “new economy” to their knees.p. It was thought that networks with distributed resource management, such as the Internet and World Wide Web, were not susceptible to failure because removal of a single node, such as a web page or router, would not affect the entire system.p. While this is true for random failure of nodes, an attack on the most connected nodes — those web pages and routers vital to maintenance of the network’s connectivity — would drastically reduce the ability of the remaining nodes to communicate with each other, according to a report in today’s Nature.p. The vulnerability of the Internet and World Wide Web to attack is a result of their network structure. They are “scale-free” networks; most of the nodes have one or two links, whereas a few nodes have a large number of links and so play a key role in the behavior of the network. Removal of a few highly connected nodes could cripple the system.p. Scale-free networks differ from “exponential” networks. In exponential networks, each node has roughly the same number of connections and thus no particular node holds much weight. Removal of any node makes it more difficult for the other nodes to communicate about the difference between two common transportation networks:the U.S. highway system and the U.S. airline routing map," said Albert-Laszlo Barabasi, an associate professor of physics at the University of Notre Dame in Indiana and co-author of the Nature study.p. Two to six highway links serve most cities in the highway system; a few have more and none have less than two. That is a fairly homogenous network, like an exponential one, said Barabasi.p. The majority of airportsare small, with two to four links, but they all connect to a few very large hubs that have hundreds of links.p. “While it is not clear that the airline system is indeed a scale-free network, they have generally the same characteristics regarding the important role the hubs play, in contrast with the exponential networks,that are very democratic since all nodes look pretty much the same,” he said.p. Since there are many more nodes with just a few links than highly connected nodes in a scale-free network, there is much greater probability that a random failure will affect a small node than a big node inthe network. This inherently protects scale-free networks such as the Internet from being debilitated by random failures.p. “However, the structure that makes the scale-free network superior to the exponential network in the case of random error becomes its Achilles’ heel under hostile attack,” writes Yuhai Tu of the IBM T.J. Watson Research Center in Yorktown Heights, New York, in a Natureperspective on the research.p. Barabasi hopes this research will be used to increase Internet security.Tu thinks the research provides a useful framework to qualitatively describe and analyze complex network systems such as gene regulatory networks.p. “Perhaps if we could understand why certain network topology is preferred and selected by nature, such knowledge could ultimately help us design more robust artificial systems,” he concludes.p. July 27, 2000

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