Comment Re:So... (Score 2) 91
b) Exit nodes don't matter for blocking purposes. Bridge nodes are discoverable, but Tor has made them difficult to discover the complete set, https://bridges.torproject.org/ (or, since that'll be blocked in most useful places, emailing bridges@torproject.org with the "get bridges" in the body) only gives out a few at a time with a captcha requirement, and only sends to https-enabled webmail hosts.
Tor also has an unknown number of private bridges people run and disseminate through their own channels to friends and family and so on. This, plus obfsproxy and related tricks like the flashproxy work from Stanford, make it really really difficult to discover and block enough bridges into the network.