> That's not how I interpreted the request. I took the point as "IPv6 as a standard should have been designed to take an IPv4 address and convert it reliably to

> That's not how I interpreted the request. I took the point as "IPv6 as a standard should have been designed to take an IPv4 address and convert it reliably to a specified IPv6 address, which we would set up to route to the same location." That is, old software that requested an IPv4 address could have it translated by the OS into an IPv6 packet before transmission deterministically It appears you are asking for the "IPv4-mapped IPv6 addresses", which are of the form ::ffff:x:y, where xy is the 32-bit IPv4 address (there's even a special text format for these addresses, you can use ::ffff:a.b.c.d instead of having to convert the IPv4 address to hexadecimal). The only difference from what you are asking is that these addresses are routed through the IPv4 network; they allow applications written with only IPv6 in mind to still work with IPv4 networks. Or you might be thinking of something like SIIT (Stateless IP/ICMP Translation), which uses addresses of the form ::ffff:0:x:y (which can also use the same kind of special text format as above).