Cannot resolve DNS hostname with many records

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.