[tor-bugs] #18605 [Core Tor/Tor]: Consider including fallback directory mirrors with multiple IP addresses

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#18605: Consider including fallback directory mirrors with multiple IP addresses
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 Reporter:  teor          |          Owner:  teor
     Type:  enhancement   |         Status:  new
 Priority:  Medium        |      Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:  3
 Reviewer:                |        Sponsor:
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Comment (by teor):

 Replying to [comment:7 nickm]:
 > Here's a silly question: Can we just include the fallback twice, with
 two different addresses?

 Yes, it's the fallback selection process that needs changes, not tor
 itself:

 Replying to [ticket:18605 teor]:
 > ...
 > This will require changes to the fallback selection script and the
 whitelist format.

 And it's safe (for reliability) to list the same fallback twice, as long
 as it's only some fallbacks that get this treatment. Ideally, we'd want
 users to get at least 1 fallback or authority on an alternate IP address
 before it fails bootstrap or the user gives up (nominally 30 seconds).

 Authority: 2*2/8 = 50%
 Fallback: 4*N/150 = 50%

 With N = 19, or 1/8 of fallbacks on alternate IP addresses, most clients
 would get at least one on an alternate address every bootstrap.

 The challenge will be contacting each operator, and finding some operators
 with multiple IP addresses. We might even contact all *potential*
 operators, and then select two different lists, so we don't miss eligible
 relays with multiple IP addresses.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18605#comment:8>
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