> contrast the success of HTTP/2 with the failure of IPv6 to maintain backward compatibility at the API level Unfortunately, it was not possible for IPv6 to ma

> contrast the success of HTTP/2 with the failure of IPv6 to maintain backward compatibility at the API level Unfortunately, it was not possible for IPv6 to maintain backward compatibility with IPv4 at the API level. That's because the IPv4 API was not textual; it was binary, with fixed-size 32-bit fields everywhere. What they did was the next best thing: they made the IPv6 API able to also use IPv4 addresses, so that new programs can use a single API for both IPv4 and IPv6.