A number of Chinese netizens report that since May 6 2011 visiting overseas website via China Telecom and China Unicom has become highly unstable. This time the disruption mainly affected corporate connections, including university, while ADSL connection at home performs normally.
Some technology bloggers point out that the Great Fire Wall is now able to monitor data flow of local IP and impose restriction when it detect large amount of access to certain overseas IP addresses. Some are worried that the mechanism may result in a de facto white listing of overseas websites.
Corporate and university connection affected
Prominent Technology blogger William Long points out that the blocking this time is targeted at corporate user in order to stop people from visiting overseas website via corporate network and connection.
He runs a test in his office at Shenzhen and found out that he cannot connect to certain overseas IP addresses (119.145.47.102). Below shows the detail of the test results:
The Southern Medical University also has suffered from the disruption and explained the situation that China Telecom has restricted the IP access of the university to overseas websites. Zhejiang University also has similar problem [zh], the school VPN's overseas connection has been disrupted. (via William Long)
Data flow monitored
In Sina Microblog, many re-post the following information:
国内各大互联网公司纷纷出现网络问题，目前已知的包括百度、腾讯、阿里巴巴和若干子公司，对于国外网站的访问受限，其中包括苹果的app store也无法正常连接。有人分析说这次断网可能是因为墙已经具有了探测和分析大量加密流量，并对IP地址执行封锁，各大互联网公司的出口被封也在其中。
VPN and circumvention tools forbiddened
In order to tackle with the problem, the IT department of certain corporate has issued the following notices: (via Twitter user @yegle)
“建議大家在訪問國外網站時，只訪問和工作有關的網站，不要使用「翻牆」之類的軟件。
仔细看了IT的邮件，在最后IT说了，访问国外网站需要提供域名，IP地址以及访问原因。
原文转载：各位同学， 请大家在使用公司内部网络时，不要使用翻墙工具和VPN等方式访问境外网络信息。 此行为可能导致公司网络出口被封（如：google，msn等正常境外网络访问不稳定），并会为公司和个人带来不必要的麻烦。 请大家在日常工作中一定注意避免。
A notice from the Chinese Academy of Sciences has confirmed netizens’ speculation:
中科院IHEP： 这两天我所网络连续发生短暂无法访问国外资源的现象，经检查确认我所部分用户使用翻墙技术访问非法资源导致网安部门将我所IP地址临时列入黑名单。在此再次提醒大家严格遵守网络使用规范，不要使用非法手段访问敏感/非法网络资源！
21 comments
In a rare interview, Fang Binxing, the creator of the “Great Firewall”, has admitted to having six VPNs on his home computer to “test which side wins: the GFW or the VPN.”
http://www.digitaltrends.com/computing/architect-of-chinas-great-firewall-gives-rare-interview/
Since many Chinese businesses and education centers use VPNs to protect their assets, this interference with VPN bandwidth will be deliciously ironic.