This ticket depends on relay IPv6 extends in legacy/trac#33220. We reserve Tor subprotocol "Relay=3" for tor versions where: * relays may perform IPv6 extends, and * bridges might not perform IPv6 extends, as described in this proposal. See proposal 311, section 5: https://gitweb.torproject.org/torspec.git/tree/proposals/311-relay-ipv6-reachability.txt#n601