[goatinaboat]

How would it have possibly been backwards compatible? Plenty of routers and ip-aware switches have, in hardware, specified that ips are 32-bits, so anything that added more bits would necessarily break existing hardware, and thus not be backwards compatible.

Easy, just declare that the entire IPv4 address space is ::x.x.x.x in IPv6 and Bob’s your uncle. No idea why they didn’t do this other than sheer solipsism.

[jlgaddis]

> Easy, just declare that the entire IPv4 address space is ::x.x.x.x in IPv6 and Bob’s your uncle. No idea why they didn’t do this other than sheer solipsism.

They did [0,1]:

  The "IPv4-Compatible IPv6 address" was defined to assist in the IPv6
  transition.  The format of the "IPv4-Compatible IPv6 address" is as
  follows:

  |                80 bits               | 16 |      32 bits        |
  +--------------------------------------+--------------------------+
  |0000..............................0000|0000|    IPv4 address     |
  +--------------------------------------+----+---------------------+

  Note: The IPv4 address used in the "IPv4-Compatible IPv6 address"
  must be a globally-unique IPv4 unicast address.

  The "IPv4-Compatible IPv6 address" is now deprecated because the
  current IPv6 transition mechanisms no longer use these addresses.
  New or updated implementations are not required to support this
  address type.

--

[0]: https://tools.ietf.org/html/rfc4291#section-2.5.5.1

[1]: https://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresse...

[wmf]

This sounds like it works but when you get into the details it gets ugly.

http://archive.is/eHvKF

HN discussion: https://news.ycombinator.com/item?id=10854570