http://y7egb5vi45k74makeixpfb7jnimfxm3gf233lb3ke2ldonozjk55nvad.onion/notes_on_dns.html
Because this is a pain in
the ass to type, dig has the special syntax dig -x [ip] to make this
simple. The long form is provided here only for demonstration. dig 243.19.161.107.in-addr.arpa PTR
...
243.19.161.107.in-addr.arpa. 86400 IN PTR lainchan.org.
...