Keith Moore writes:
IPv4-only hosts cannot communicate directly with IPv6-only hosts.
Irrelevant. The only hosts under discussion are hosts where the software
RFC 2893 explains how two of these hosts, one with an IPv4 address and
the other with an IPv6 address, can communicate with each other.
Naturally, the details include a mechanism for routing an encoded IPv6
packet through the IPv4 network to the IPv6 network. This is not rocket
What you are proposing, whether you understand it or not, is a foolish
duplication of the same feature in every higher-level protocol, making
unnecessary work for application writers and system administrators.