Clients may bootstrap from a default fallback directory mirror

   Each client maintains a list of directory authorities.  Insofar as

   possible, clients SHOULD all use the same list.

  [Newer versions of Tor (0.2.8.1-alpha and later):

   Each client also maintains a list of default fallback directory mirrors

   (fallbacks). Each released version of Tor MAY have a different list,

   depending on the mirrors that satisfy the fallback directory criteria at

   release time.]

   Clients try to have a live consensus network-status document at all times.

   A network-status document is "live" if the time in its valid-until field

   has not passed.

   When a client has no consensus network-status document, it downloads it

   from a randomly chosen authority.  In all other cases, the client

   downloads from caches randomly chosen from among those believed to be V3

   directory servers.  (This information comes from the network-status

   documents; see 6 below.)

   from a randomly chosen fallback directory mirror or authority. Clients

   prefer fallbacks to authorities, trying them earlier and more frequently.

   In all other cases, the client downloads from caches randomly chosen from

   among those believed to be V3 directory servers.  (This information comes

   from the network-status documents; see 6 below.)

   After receiving any response client MUST discard any network-status

   documents that it did not request.

   (Note: clients can and should pick caches based on the network-status

   information they have: once they have first fetched network-status info

   from an authority, they should not need to go to the authority directly

   again.)

   from an authority or fallback, they should not need to go to the authority

   directly again, and should only choose the fallback at random, based on its

   consensus weight in the current consensus.)

   To avoid swarming the caches whenever a consensus expires, the

   clients download new consensuses at a randomly chosen time after the