[tor-bugs] #33009 [Core Tor/sbws]: sbws bandwidth scans should require a minimum exit bandwidth

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#33009: sbws bandwidth scans should require a minimum exit bandwidth
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     Reporter:  teor           |      Owner:  (none)
         Type:  defect         |     Status:  new
     Priority:  Medium         |  Milestone:  sbws: 1.1.x-final
    Component:  Core Tor/sbws  |    Version:  sbws: 1.1.0
     Severity:  Normal         |   Keywords:  sbws-majority-blocker
Actual Points:                 |  Parent ID:
       Points:  1              |   Reviewer:
      Sponsor:                 |
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 When sbws is constructing a two-hop measurement circuit to run a test, it
 tries to pick an exit that has at least twice the consensus weight of the
 current relay-under-test:
 https://github.com/torproject/sbws/blob/master/sbws/core/scanner.py#L216

 So this means that in this case, sbws would have picked any exit that was
 not a BadExit, has an acceptable ExitPolicy, and has a consensus weight of
 at least, well, 2.  That's not a lot.

 As it turns out, something like 10% of exits have under a 600Kbyte/sec
 advertised bandwidth.  So it seems pretty easy from this weight=1
 bootstrap scenario to get paired with an exit that will give poor test
 results.

 Perhaps bwauth path selection should also choose a testing pair from
 exits/relays with a certain absolute minimum of weight or advertised
 bandwidth?

 Reported by Jimmy on tor-relays:
 https://lists.torproject.org/pipermail/tor-relays/2020-January/018027.html

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33009>
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