At the sametime, even somebody does not like it, because RFC3484 is standard NOW,
so I admit to say that any application on one router CPE is still recommeded to
select its source address from addresses assigned to the WAN i/f.
Especially, Mikael, how do you fix it ? This is still you have not answer yet.
OK. Let me clarify what I want to say.
I am recommending that following (A)+(B) as the way we go
to allow all the implementation which is compatible with today's standard set
can be compatible with the service.
(A)A global IPv6 address is recommened to assign the WAN i/f to a CPE router or a
host that terminates upstream link
(B)Prefixes should be delegated by DHCPv6 to (especially) a CPE router
Even if some ISP does not do assign global IPv6 address to the CPE,
that's up to that ISP.
But their customer should be noticed that some machine which is compatible
IPv6 standard specification can not work correctly if that terminates upsteam link.