# https://wiki.archlinux.org/index.php/IPv6_tunnel_broker_setup
# https://forums.he.net/index.php?topic=3153.0
# https://gist.github.com/pklaus/960672
# https://shorewall.org/6to4.htm#idm143
# https://genneko.github.io/playing-with-bsd/networking/freebsd-tunnelv6-he
# https://journeymangeek.com/?p=228
# https://superuser.com/questions/1441598/using-a-hurricane-electric-tunnel-to-provide-ips-to-a-network-with-dnsmasq/1441604#1441604