Jonathan Zittrain on how filtering for spam etc. undermines the E2E principle
“Saudi Arabia, for example, is quite open about the fact that all network traffic going into and out of the kingdom is routed through a central farm of proxy servers. Instead intermediaries could do this so long as they can be enticed–or coerced–to apply exceptions to the end-to-end rule of “whatever this data is, help get it to where it’s going.”
Documenting the new crop of discerning Net couriers among the old-time end-to-enders isn’t easy. Any number of problems might prevent someone from reaching a requested Web page or other Internet resource, including network congestion, misconfigured servers or broken routers.
How, then, can you know when a blockage is due to the explicit filtering of content somewhere within the network at someone else’s initiative? To complicate matters, filtering can take place anywhere along the line that extends from one’s own computer to one’s ISP to intermediate carriers to the destination’s ISP to the destination server itself. ”