  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.
