How Big is the Great Firewall of China or China’s DNS Censorship Assessment

Great Firewall

The work of the content filtering system in China is far from perfect, experts say.

The Golden Shield content filtering system, or the so-called Great Firewall of China, used by the Chinese government for censoring purposes, is far from ideal. In short, the system blocks what is unnecessary and does not block what is needed. This is the conclusion reached by a group of experts from the University of Stony Brook, the University of Massachusetts, the University of California and the Citizen Lab at the University of Toronto following the results of the study “How big is the Great Firewall of China? An Assessment of DNS Censorship in China ”.

The team used their large-scale GFWatch platform, which tests hundreds of millions of domains every day, allowing them to continuously monitor how DNS traffic is being filtered in China. Within nine months, using GFWatch, researchers tested 534 million domains and found that only 311,000 of them were censored by the Golden Shield.

“To our knowledge, this is the largest number of tested and censored domains ever described in the literature,” the researchers noted.

Experts also found out that due to incorrect filtering rules “for the company” with censored domains, 41 thousand allowed domains are mistakenly blocked. Recall that users in Russia also faced a similar problem in March of this year, the code, by slowing down Twitter, Roskomnadzor slowed down all sites with “” in the domain, including, podcast sites Beardycast and Zavtracast, subdomains Github and Steam.

Among other things, as it turned out, the “Golden Shield” blocks 77 thousand domains outside of China. The reason is that during the blocking process, the equipment does not drop the connection and does not display the notification “Access is restricted by the request of the court”, but simply gives users different addresses in response. Very often, non-Chinese public DNS servers, including those of Google, Yandex and Cloudflare, “remember” these addresses and distribute them to international users.

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