With respect to dual-stacks, the thing I'd like to have is the Mobile IPv6 MN-HA tunnel to be a v6-in-v4 tunnel instead of v6-in-v6
My concern is this: we already have about half a dozen IPv4 NAT traversal techniques (IPsec, MIPv4, STUN, TURN, a number of others) -- and some have been proposed to allow IPv6-in-IPv4 tunneling to also traverse NAT (none taken up by this WG, at the moment, though.).
So you want to implement and specify one for dual-stack Mobile IPv6 *too*?
No, I want Mobile IPv6 to not require its MN-HA tunnel to be v6-in-v6 but to require it to be either v6-in-v6 or v6-in-v4.
My _personal_ two top priorities in this context:
1) make sure NAT traversal stays an _IPv4_ problem.
Traverse a NAT to get a global IPv4 address, then activate an IPv6 transition mechanism. Everything is transparent to the IPv6 transition mechanism.
2) failing that, provide *one*, *very simple* (most likely, a bidirectional tunnel or something like that) mechanism which is close
to bulletproof to enable IPv6 tunneling over NAT. When you have an
IPv6 connectivity, you don't have to worry about NAT's anymore in any
of the scopes listed above (MIP, IPsec, etc.etc.).
Sounds like a good stepwise scheme, provided that one can identify that most simple bullet-proof mechanism, and that mechanism is not an "IP over SMTP" April's fool.