summarizing [#15937](https://trac.torproject.org/projects/tor/ticket/15937) ([diff](https://trac.torproject.org/projects/tor/wiki/org/sponsors/SponsorR/Re achability?action=diff&version=4)) URL: https://trac.torproject.org/projects/tor/wiki/org/sponsors/SponsorR/Reachability?version=4