https://ggus.eu/ws/ticket_info.php?ticket=100064
See GGUS ticket:
https://ggus.eu/ws/ticket_info.php?ticket=100064#update#26
and:
https://github.com/italiangrid/voms/blob/9f10867bafc6229c45cc989425770240683cf6de/src/socklib/ipv6sock.cc#L45