All traffic to/from some IP addresses is blocked, additionally all Chinese DNS servers respond with random A records when the domain name is banned, for example:

  $ host facebook.com 202.97.0.6
  facebook.com            A       8.7.198.45
  $ host facebook.com 202.97.0.6
  facebook.com            A       243.185.187.39
  $ host facebook.com 202.97.0.6
  facebook.com            A       243.185.187.39
  $ host facebook.com 202.97.0.6
  facebook.com            A       46.82.174.68
  $ host facebook.com 202.97.0.6
  facebook.com            A       59.24.3.173

(202.97.0.6 is an open resolver in China)