I know its the same, but from UX standpoints looks different. Anyway, that was just one example. As for IPv6 -> IPv4 (note the arrow) its pretty much easy. IPv6 have much bigger address space, so it can embed IPv4 addresses in special interop subnets that are routed to special NAT GW that handle IPv6 -> IPv4 translation. Thats right, its one way. IPv4 -> IPv6 is pretty much impossible. But do we need one? Todays internet is centralized, a lot of traffic goes into cloud, not between users. Also, transition is not 0 -> 1, its gradual. Same about users. Some even dont really understand what they are using, happy that netflix or facebook opens. There are of course power users, so they will go different transition path. Dont put everyone into same bucket. As for content providers (servers) they can stay for IPv4 for a while, become dual stack or even (once a traffic level shifts) provide IPv4 -> IPv6 balancers to handle leftovers of IPv4 traffic. Also, not all services can work via proxying/balacing. Some services needs to be dual stack from the start. As for RFC1918, because why not? Why are you forcing me to run my networks your way? Its mine network and I want to set it up the way I see fit. Not everyone is going to ask RIPE/LIR was address space for his small network. Isnt that too much burden? ---------- Original message ---------- From: Owen DeLong <owen@delong.com> To: borg@uu3.net Cc: nanog@nanog.org Subject: Re: V6 still not supported Date: Fri, 18 Mar 2022 13:44:13 -0700 This shows a fundamental lack of understanding˙˙ Netmask and Prefixlen/CIDR are just Different ways of representing the exact same thing. While it˙˙s true that prior to CIDR, one COULD implement discontiguous net masks, this was rare in actual practice and had no real use, so nothing was lost in eliminating that capability. Internal to the operating system, regardless of whether presentation is as a CIDR length or a netmask, it˙˙s still stored and compared against addresses as a bitfield. Client A has a 128 bit address. Client B has a 32 bit address and does not understand packets with 128-bit addresses. Please explain how these two clients interoperate. That is literally what you are asking for here. Math says it doesn˙˙t work. Why? Why does RFC-1918 space need to exist at all? Why not simply use transparent addressing and stop mutilating packet headers? However, if you really think this is important, I will refer you to what is called ULA in IPv6. It˙˙s pretty much all the same problems of RFC1918 minus the high probability of collision when merging two networks. I think you have over-valued it. Owen