Comment #42069 on "HN doesn't understand the Internet Protocol". This opinion is frequently repeated here on HN but -- you CAN'T use IPv4 internally and expect to talk to external IPv6 hosts.

How would this IPv4 internal host (say 192.168.1.10) send a packet destined to 2001:db8::1? You can't stick a 128-bit IPv6 address into your IPv4 packet - there are only 32 bits available for the destination address inside its header.

NAT is not magic, it cannot extract a 128-bit number out of your 32-bit number.