[tor-bugs] #11741 [Tor]: Cannot resolve DNS hostname with many records

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#11741: Cannot resolve DNS hostname with many records
--------------------------------+-------------------------------
 Reporter:  T(A)ILS developers  |          Owner:
     Type:  defect              |         Status:  new
 Priority:  normal              |      Milestone:
Component:  Tor                 |        Version:  Tor: 0.2.4.21
 Keywords:                      |  Actual Points:
Parent ID:                      |         Points:
--------------------------------+-------------------------------
 Hi,

 today, the hostname used for the Tails mirrors pool (dl.amnesia.boum.org)
 has 31 A records.

 It can be successfully resolved using non-Tor resolvers, but the Tor
 resolver fails to return anything useful.

 {{{
 $ tor-resolve dl.amnesia.boum.org
 May 05 10:15:34.891 [warn] Got SOCKS5 status response '4': host is
 unreachable
 zsh: exit 1     tor-resolve dl.amnesia.boum.org
 }}}

 ... and TBB times out with "Firefox can't establish a connection to the
 server at dl.amnesia.boum.org." when trying to connect to
 http://dl.amnesia.boum.org/. Note that ttdnsd works fine.

 I suspect that's because we have reached the point when the DNS reply
 needed to answer the request exceeds the default maximum size of a UDP
 datagram (512 bytes). Perhaps the Tor DNS resolver fails to fallback to
 TCP, or to specify/handle larger UDP datagrams with the EDNS extension?

 As a temporary workaround, I'll drop a few mirrors from our DNS round-
 robin pool, but given how quickly the amount of Tails downloads grows
 these days, it would be good for us to see our mirrors pool grow
 accordingly (which does happen, until this point). I'll report back to
 confirm if this workaround does the job.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11741>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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