Windows implementation is the reference implementation, as it was
Microsoft who authored RFC 3484 to begin with.)
Does that mean that this policy will prefer a NAT44 IPv4 over a
configured tunnel?
Yes, that the effect of the change proposed in
draft-arifumi-6man-rfc3484-revise-02, and also how Microsoft's
getaddrinfo() currently behaves. I strongly support the proposed change.
RFC 3484, however, currently says to prefer 6to4 over IPv4 NAT44 (or
more precisely RFC 1918 IPv4).
A 6to4 router (like an Airport) could stop advertising the prefix
when the 6ro4 default router is unreachable, but nobody does that.
Nope. However, if 6to4 was only used by the end-user operating
system/applications as a last resort connectivity method, this would not
be necessary. And that is clearly the _intention_ of RFC 3484, which
says to ?avoid the use of transitional addresses when native addresses
are available?. I suppose NAT44 wasn't used as widely as now back when
the RFC was written.