> There was a third option: make the existing IPv4 space a hierarchically routed island of the new IPv4.1 space, with backwards compatible packet format, then u

> There was a third option: make the existing IPv4 space a hierarchically routed island of the new IPv4.1 space, with backwards compatible packet format, then upgrade just the endpoints in the first phase. Do you mean applying some kind of network address translation? > So every owner of a ipv4 would get, say, an entire 32 bit space that routes over existing IPv4 infrastructure. So, if the endpoints are upgraded, you have guaranteed end-to-end deliverability without silly hacks such as NAT or STUN. Ahem.