http://magma.ua4vjlx72wv5crhkificaeysp62hizhazipfshsdvs6jxqvhtkpllcad.onion/guide/data-analysis.html
Tor clients can choose a path through the network and build
a secure circuit in which each node (relay or onion router) in the path knows
its immediate predecessor and successor, but no other nodes in the circuit. The
Tor network relies on directory authorities to operate, thus it is essential for
these directory authorities to be reachable from other Tor relays.