Just a heads' up that tor 0.2.8 includes a fallback directory mirrors feature, where tor clients bootstrap from a set of hard-coded long-lived directory mirrors. This makes bootstrap more reliable, and makes it harder to block tor. The wiki has an entry with more details. [0]

We're currently trying to finalise a list of around 100 fallback directory mirrors by the time tor 0.2.8-stable is released. [1]

If we have this many mirrors, I am confident we won't overwhelm any of the mirrors when an app like Orbot, Tor Browser, or Tails switches to tor 0.2.8. (Are there any other tor apps with millions of users that I've missed?)

If this feature does cause problems, or if your app needs to bootstrap only from the authorities (Tails time syncing? [2]), the fallback directory mirrors feature can be disabled using the tor config option "UseDefaultFallbackDirs 0".

Tim

[0]: https://trac.torproject.org/projects/tor/wiki/doc/FallbackDirectoryMirrors

[1]: https://trac.torproject.org/projects/tor/ticket/17158

[2]: https://tails.boum.org/contribute/design/Time_syncing/