Yes, I know about this mapping (I can read man pages too), but a) ping6 ::ffff:127.0.0.1 doesn't work too; b) it's not an IPv4 address, because the binary rep

Yes, I know about this mapping (I can read man pages too), but a) ping6 ::ffff:127.0.0.1 doesn't work too; b) it's not an IPv4 address, because the binary representation of ::ffff:127.0.0.1 != 127.0.0.1. It's the IPv4 address space mapped to an IPv6 address space (IPv4-mapped-on-IPv6). c) IPv4 addresses in IPv6 address space are deprecated: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.1 https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.... . In short, IPv6 and IPv4 cannot coexist, so they must be separated, so we must keep IPv4, because it's mandatory, and we may skip IPv6, because it's optional. So, all internet providers in my area are skipping IPv6, because they can. All that problems are created by lack of backward compatibility in IPv6 protocol. Why? «Because backward compatibility with IPv4 is unnecessary. IPv6 is so much better. Everyone will jump to IPv6 till end of the next (1995) year.»