I've talked from v4 clients to v6 servers before, and I've accepted v4 connections to v6 servers. How can it be so clear that it's not possible when I've done it before?
> As for TUBA, the transition plan incorporated tunneling
The transition plan for v6 also incorporates tunneling (6in4 is the same thing as the EON tunneling described in the draft you linked), so again I ask why TUBA counts as having a sane transition plan when doing the same things in v6 doesn't.
There's not much administrative overhead involving in transitioning a network to v6. For most people it involves doing exactly no extra work beyond what they already do to deploy v4. Of course, you do need to reconfigure anything that's been configured such that it can only work with v4 (and this might be quite a lot of stuff), but that was always going to be necessary no matter what you're transitioning to.
> As for TUBA, the transition plan incorporated tunneling
The transition plan for v6 also incorporates tunneling (6in4 is the same thing as the EON tunneling described in the draft you linked), so again I ask why TUBA counts as having a sane transition plan when doing the same things in v6 doesn't.
There's not much administrative overhead involving in transitioning a network to v6. For most people it involves doing exactly no extra work beyond what they already do to deploy v4. Of course, you do need to reconfigure anything that's been configured such that it can only work with v4 (and this might be quite a lot of stuff), but that was always going to be necessary no matter what you're transitioning to.