The study from Harvard University's Berkman Center highlights how modern Web standards have permitted thousands of domain names to share one Internet address. It concludes that instead of precisely targeting only objectionable sites, attempts to restrict Internet addresses with pornographic, political or gambling-related content inevitably make legitimate sites unreachable too.
"The numbers are staggeringly high," said Ben Edelman, a student fellow at the Berkman Center and author of the report. "According to my results, two-thirds of sites are hosted on Web servers with 50 or more domain names."
The research comes as state and national governments weigh methods to restrict Web sites that may be legal in other jurisdictions but not theirs.
In September, a Pennsylvania judge previous study that China had blocked at least 19,000 Web sites in categories including news, health, politics and entertainment.WorldCom to block access to some offshore Web sites allegedly featuring child pornography, a move that forced WorldCom to disable those Internet addresses for all North American customers. Edelman found in a
The original version of the Hypertext Transfer Protocol (HTTP) required each Web site to have its own Internet address, which maps domain names like News.com to numeric values such as 22.214.171.124. In response to a perceived shortage of addresses, HTTP 1.1 in 1999 permitted each Internet address to host an arbitrary number of Web domains.
However, current Internet technology allows Internet service providers or backbone providers to block only by IP (Internet Protocol) addresses, not domain names or URL.
Edelman's study says the practice of Web sites sharing IP addresses is so commonplace that blocking raises free-speech problems. His data show, for instance, that Yahoo hosts 74,000 Web sites at one address; Tucows.com uses one address for 68,000 domains; and Namezero.com points 56,000 domains to one address. "More than 85 percent of active domain names are found to share their Web servers with one or more additional domains," the study says.
In Pennsylvania, a state law that took effect last year permits the attorney general to order Internet providers to block access to Web sites suspected of featuring child pornography.
Sean Connolly, a spokesman for the Pennsylvania attorney general's office, said on Wednesday that the law "has been very successful" and has led to few complaints. "We've worked with Web hosting companies and ISPs to ensure that the illegal and offensive material is taken down and not any legal sites that may share that space," Connolly said.
A WorldCom representative declined to comment until Edelman's study became public.
Stewart Baker, an attorney at Steptoe and Johnson who represents the U.S. Internet Service Provider Association, said the study's findings were surprising.
"I certainly had no idea how many Web sites had common IP addresses so that if you were blocking a particular IP address you might be picking up dozens of Web sites," Baker said. "It's quite troubling given the growing issue of blocking IP addresses around the world as a solution for content that people don't like."