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There is a straight-forward mapping of the IPv4 address space into IPv6 (you can do ping6 "::ffff:127.0.0.1"), and for new development that is also by far the e

There is a straight-forward mapping of the IPv4 address space into IPv6 (you can do ping6 "::ffff:127.0.0.1"), and for new development that is also by far the easiest way to support both protocols: the application does everything in IPv6, and without writing a single line of code, the OS takes care of transparently using IPv4 when needed. There is no mapping back from IPv6 to IPv4 (so IPv6 is backwards compatible, but not forwards compatible), but it can't be because the whole point is to have a larger address space.

anilgulecha 9y ago
Backward compatible means that a valid IPv4 address (127.0.0.1) should, by definition, be a valid IPv6 address. Hence IPv6 is definitely not backward compatible.
- merb 9y ago
  but it is (even adding a prefix) means that it is backwards compatible in some way.
  - efreak 9y ago
    Not as long as every preexisting application on your computer validates IP addresses and tells you that colons are not valid in IPs and domains.