> The failure of IPv6 is also the success of IPv4 engineering. When IPv6 was designed in the mid 90s, there were many issues that might hold back IPv4 down the

> The failure of IPv6 is also the success of IPv4 engineering. When IPv6 was designed in the mid 90s, there were many issues that might hold back IPv4 down the road. Another big part of it is that all of the features of IPv6 except the address length change were back-ported to IPv4 (e.g. address auto-assignment and IPsec) removing the carrots and leaving only the "stick" of the IPv4 address shortage (which barely registered at all until a few years ago) to push people to v6.