> But to use "new" packets, EVERY SINGLE ROUTER in the path between them has to be able to understand "new" packets, else it will be dropped. How do you solve it?
You are saying this like it's not the case with the current plan. Every single router needs to understand the new way. Of course.
But guess what, right now, all these supposed routers have _nothing_ to route, because nobody even has an IPv6 address. Should the other plan been followed, _everyone_ would already have one (i.e. their old IPv4 address) and _everyone_ would be capable of sending such packets (current situation where I have unconfigured, parellel IPv6 stack means nothing - I cannot use it as is). And even if they do have an IPv6 address now, it's useless - there is nothing to see with IPv6.
In the alternative scenario, ISPs have an _incentive_ to be able to route IPv6 - all of their current and prospective _customers_ are on it. Right now, they don't.
So, of course they would have made sure that every single router can route. What better alternative would they have? Build layers of NAT when everyone already is on IPv6? What the hell for?
Also note that issuing IPv6 addresses to new customers is a no brainer. Issuing IPv6 addresses to new customers now is what - interoperability failure?
> Suppose you have a "new" host sending to a host with an "old" address. It has no way of knowing the host with the "old" address can understand "new" packets
Of course it has. Everyone has been upgraded already. Any destination that didn't (there would be no reason for them not to - they would get all this as part of regular updates) would be simply unreachable for "new" hosts. The amount of those would be very small indeed.
You see, one of the main problems with the current plan is that IPv6 is the "other" thing. The other network config nobody understands. The other firewall nobody understands. The other routing config nobody understands. The other thing nobody cares about. Should IPv6 have been "the" thing, people with networks that "do" things (i.e. not ISP) would automatically care for it. It would be their one and only network, they spent all of their time building. You think they would not want their ISPs to route this?
There would be no 99% of users that are supposed to ask their ISPs to give them an IPv6 address. All these folks would _be_ IPv6 users already.
> And 8 years is not nearly enough.
The problem was identified 20 years ago. DJB (who I am not particularly big fan of) wrote his piece 8 years ago as a reaction to a disastrous plan unfolding right in front of his eyes. So, your timeline is not quite right. There would have been even more time to do this.
You are saying that you see this upgrade path as the same failure. You know what, this is 100% incorrect. At least everyone would have their host configured for IPv6 _right_ _now_, even if routing wasn't done yet. At least there would be an incentive to turn the pressure up on ISPs, so that the problem gets solved. Precisely because all of the edge (where the value is) would be done and ready. In the end, ISPs have to route the traffic for their customers - what else are they going to do?
Current plan produced no such incentive. That's exactly why ISPs are talking of layers of NAT and what not.
Yeah, unfortunately in this case, it's not you or anyone else commenting here, but rather folks supposedly in charge of making things work. Or should I say, not work. :-)
But you are right. I should not post on this topic any more. Maybe I should just acknowledge that the current situation is a wonderful success. Never mind that Cerf and Huston are telling us it's a bloody disaster. Hey, what do they now?