Internet censorship is typically enforced by authorities to achieve information control for a certain group of Internet users. So far existing censorship studies have primarily focused on country-level characterization because (1) in many cases, censorship is enabled by governments with nationwide policies and (2) it is usually hard to control how the probing packets are routed to trigger censorship in different networks inside a country. However, the deployment and implementation of censorship could be highly diverse at the ISP level. In this paper, we investigate Internet censorship from a different perspective by scrutinizing the diverse censorship deployment inside a country. Specifically, by leveraging an end-to-end measurement framework, we deploy multiple geo-distributed back-end control servers to explore various paths from one single vantage point. The generated traffic with the same domain but different control servers' IPs could be forced to traverse different transit networks, thereby being examined by different censorship devices if present. Through our large-scale experiments and in-depth investigation, we reveal that the diversity of Internet censorship caused by different routing paths inside a country is prevalent, implying that (1) the implementations of centralized censorship are commonly incomplete or flawed and (2) decentralized censorship is also common. Moreover, we identify that different hosting platforms also result in inconsistent censorship activities due to different peering relationships with the ISPs in a country. Finally, we present extensive case studies in detail to illustrate the configurations that lead to censorship inconsistency and explore the causes.

翻译：互联网审查通常由当局实施，旨在对特定互联网用户群体实现信息管控。迄今为止，现有的审查研究主要集中于国家层面的特征分析，原因在于：（1）在许多情况下，审查由政府依据全国性政策实施；（2）通常难以控制探测数据包在国内不同网络中的路由路径以触发审查。然而，审查的部署与实施在互联网服务提供商（ISP）层面可能存在高度差异。本文通过深入探究国家内部多样化的审查部署，从一个新的视角研究互联网审查。具体而言，我们利用端到端测量框架，部署多个地理分布的后端控制服务器，以从单一观测点探索多样化路径。生成的流量（域名相同但控制服务器IP不同）可能被迫经过不同的中转网络，从而在存在审查设备的情况下接受不同设备的检测。通过大规模实验与深入分析，我们揭示了因国家内部不同路由路径导致的互联网审查多样性普遍存在，这意味着：（1）集中式审查的实施通常存在不完整或缺陷；（2）分布式审查同样常见。此外，我们发现不同的托管平台因其与国内ISP的对等关系差异，也会导致审查活动的不一致。最后，我们通过详实的案例研究具体阐释导致审查不一致的配置，并探究其成因。