> It _was_ possible to create an address space extension that was IPv4 backwards compatible How? People keep claiming this, but I've yet to see a coherent desi

> It _was_ possible to create an address space extension that was IPv4 backwards compatible How? People keep claiming this, but I've yet to see a coherent design (either back then or today). Do you think they broke backwards-compatibility _on purpose_? What's the motivation here?