http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/283-ipv6-in-micro-consensus.html
This
happens because the microdesc consensus does not contain IPv6 ORPorts.
(IPv6-only Tor clients on versions 0.3.0.2-alpha and later use fallback
directory mirrors to fetch their microdescriptors.)
When consensus method M is used, 0.2.8.x and 0.2.9.x clients will be able
to bootstrap over IPv6-only connections using microdescriptors, without any
code changes.
4.3.2.