How does China's Great Firewall work?

I thought it was pretty simple... until I got here. I figured that when an ISP received a request for a blocked domain or domains with specific key words, that it would stop there and no response (or a bad response) would be sent back. And then with search result blocking (on Google specifically) I thought that if there was a blocked search result, Google would still return a page with unblocked links with a "Results have been blocked" type message. Boy... I think I underestimated the Chinese Government.

Here are the things I've tried to reach unsuccessfully:

  • Google sites (
  • Google Docs
  • ( is OK)
  • Youtube
  • Hulu
  • Posterous
  • Blogspot
  • Twitter
  • Any Google search page when searching for anything containing "facebook"

On certain VPN's and certain proxies I am still unable to access almost all of those sites as well. That tells me, either I am completely oblivious to how proxies/VPN's work or that the censorship here is much more sophisticated than I thought.

How did I know I was successfully connected to a VPN/Proxy? Well besides being prompted for credentials and then getting a response that said credentials OK, I also used a tool to figure out my public IP. I google'd What's My IP before using any VPN's or Proxies and kept that page up, and after connecting to a VPN or going through a proxy I figured out what my IP was again. Each time, the public IP my browser showed me was different, but without any VPN/proxy the IP was the same. So this told me I was accessing the internet through a different server. And in addition to that, I used a tool to verify that those new IP's originated from somewhere within the U.S.

So what happened when trying to access the internet through VPN's and Proxies? Well to be clear I tried, unsucessfully of course, to get around the Great Firewall with an NYU VPN, Home server VPN, UPenn VPN, and NYU Proxy. Again each verified that I was using it's public IP when accessing the internet. And so this is what would happen: would work...sometimes Hulu would work... but none of the other blocked sites I mentioned above would work.

Why is it that certain sites would work, but most of them would not EVEN if I was tunnelling to the internet via a non-China computer?? Does China have different tiers of censorship and know which sites are the highest priority to block and then let people easily access other  certain blocked sites?

How does that work??

The other thing was that whenever I typed in any "Facebook" related query to (or .hk) the response would get blocked. And then I would be unable to access Google for another 5 minutes or so while any other unblocked site would work fine. What is that magic??

And to clarify... by "blocked" I mean I would get a response from Chrome saying that Chrome could not connect, but when I opened up any other site (mostly Hacker News) in a new tab it would render just fine.

In the end, a certain VPN (GoTrusted) did end up working for me. You have to pay, but I am currently on a 7 day free trial. Yay!