[tor-bugs] #20996 [Core Tor/Tor]: IPv6-only client fails to bootstrap on microdescriptor fetch/fallback

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#20996: IPv6-only client fails to bootstrap on microdescriptor fetch/fallback
------------------------------+-----------------------------
     Reporter:  mtigas        |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:  Tor: 0.2.9.7-rc
     Severity:  Normal        |   Keywords:  ipv6
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 For a fresh client (nothing cached) when configured with "ClientUseIPv4 0"
 + "ClientUseIPv6 1" (and client is also on a network with no external IPv4
 address).

 Hangs at 45%, Asking for relay descriptors. Running on 0.2.9.7-rc.

 Works fine with UseMicrodescriptors 0. ("ClientPreferIPv6DirPort 1" +
 "ClientPreferIPv6ORPort 1" have no affect.)

 Attaching torrc and a log @ loglevel info.

 CCing teor here since I vaguely remember having a conversation with him at
 last tor meeting where I believe he mentioned to try using
 "UseMicrodescriptors 0"; which (now that I've had a chance to test) seems
 like a good workaround at the moment.

 Can't seem to find another ticket for this exactly, and just wanted
 something to refer to (and post some logs and info on), so please excuse
 if it’s actually a dupe. Possibly related: #20916.

 On the mobile side, Apple’s starting to require that apps work in
 IPv6-only networks. And I’ve noticed that I’ve recently been assigned
 IPv6/NAT64 (with no external IPv4 address) on T-Mobile lately. But of
 course this also affects non-mobile IPv6-only networks.

 (On the other hand, I'm quite happy that this all _does_ work under IPv6
 with the "UseMicrodescriptors 0" workaround.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20996>
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