14 of 495 filtering interfaces (2.9%) are located in non-border internal ASes, all but two belonging to CHINANET provincial subsidiaries. The paper notes that CHINANET's provincial filtering architecture creates infrastructure capable of inspecting inter-provincial domestic traffic, even though there is no current evidence it is being used for that purpose.
From 2011-xu-internet — Internet Censorship in China: Where Does the Filtering Occur?
· §4.4, Table 2
· 2011
· Passive and Active Measurement Conference
Implications
Circumvention designs that route through purely domestic Chinese infrastructure to reduce latency cannot assume filtering-free paths; filtering capability in internal ASes is documented, and the architecture is already positioned for domestic expansion.
Measurement studies probing only border ASes will miss approximately 3% of active filtering devices; comprehensive topology probes must target servers in internal ASes to characterize the full filtering surface.