>> I would have preferred an IPv4 version 2, and extension to the address space of IPv4, possibly in a backward compatible way > This gets suggested all the ti

>> I would have preferred an IPv4 version 2, and extension to the address space of IPv4, possibly in a backward compatible way > This gets suggested all the time, but it's a fundamentally broken idea Agreed. It needs to be 100% backwards compatible, or else it's going to break havoc on the internet. And there's no such extension which can be made. Otherwise it would have been made by now. So if you're going to break compatibility anyway, you might do so in a way which is clearly signaled and doesn't allow for the myriad of "undefined" failure modes that a theoretical IPv4.1 is going to have.