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

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

 Replying to [comment:2 s7r]:
 > I like this, even if it's trivial to game we should at least not allow
 it by default.
 >
 > In #15775 I saw that Exit relays are also on the list. Has this changed?
 > I am having some mixed thoughts about including Exit relays in the list
 of fallback directories. My thoughts are:
 >
 > - Exit relays are more scarce (even the network might not have the exit
 capacity overloaded, there are a lot of middle relays compared to exit
 relays).

 I allowed Exit relays because some operators have under-utilised exits
 available.
 The extra load is negligible for a large relay (20KB/s = 50GB/month)

 > - Exit relays might need the extra traffic required for a fallback
 directory to serve exit circuits.

 I asked operators of under-utilised exits to opt-in.

 > - Exit relays have higher chances to be taken down (ISP gets mad because
 of abuse/blacklisting, seizures, etc.) which means (possibly) small
 performance penalties for the previous Tor releases that included them.

 Perhaps, but #4483 ensures that Tor clients try 4 fallbacks and 1
 authority in the first 10 seconds of bootstrap.

 > How will the list look like if we only consider middle relays with a
 certain minimum weight such that we will be able to hardcode them without
 any weight? I guess we still have plenty to choose from.

 I'll have a look at how this changes the final list.
 I will also add "Exit/non-Exit" to my list of diversity criteria to
 consider.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18749#comment:4>
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