[tor-bugs] #18749 [Tor]: Consider only including one fallback per operator

[Tor Bug Tracker & Wiki]

#18749: Consider only including one fallback per operator
---------------------------------------------+-----------------------------
 Reporter:  teor                             |          Owner:
     Type:  enhancement                      |         Status:  new
 Priority:  Medium                           |      Milestone:  Tor:
Component:  Tor                              |  0.2.???
 Severity:  Normal                           |        Version:
 Keywords:  029-proposed, TorCoreTeam201609  |     Resolution:
Parent ID:                                   |  Actual Points:
 Reviewer:                                   |         Points:  small
                                             |        Sponsor:
---------------------------------------------+-----------------------------

Comment (by teor):

 Replying to [comment:8 tscpd]:
 > Replying to [comment:7 teor]:
 >
 > > * same IP
 > >  * IPv4
 > >  * IPv6 (unlikely)
 >
 > Diverting fallback weight / same IP in list could be wise:
 > 2 instances running on 1 IP - 50% fallback weight each of it
 > 4 instances running on 1 IP - 25% fallback weight each of it
 > shouldnt be too hard to implement + even increase good acting
 >
 >
 > ...Sounds like there gonna be some potential useful knobs.  Also leaving
 possibility to analyse after generating the list great to hear.

 Having had experience with modifying weights, I'm reluctant to do it,
 because the results are not very transparent, and they have a complex
 relationship to the inputs and parameter choices. This makes it hard to
 reason about security, privacy, and reliability.

 I tried modifying exit weights, but that doesn't seem to be necessary for
 diversity in the current list of fallbacks. The option is still in the
 script if we decide we want to do it.

 I also tried modifying consensus weights so that the resulting client
 selection weights weren't too high. That was really complex code.
 Eventually we abolished client selection weights entirely (#17905), and I
 removed the complex code.

 See my next comment for a summary of the fallback selection process. If
 there's a particular diversity criteria you're concerned about, we can
 discuss it on tor-dev and try to reach a consensus about reasonable
 values.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18749#comment:9>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online