>> 	from IPv6 specification, you must not do this.   under IPv6,
>> 	the nexthop address has to be link-local address (starting from
>> 	"fe80").
>What specification should we refer?
>Only I can find is RFC2461 (Neighbor Discovery for IP Version 6 (IPv6)),
>but I don't think the description about link-local address applies to host.

	yes, this is redirect that matters, as far as I remember.
	(maybe "must not" was too strong, "should not"?)
	the adress of ipv6 routers (gateways) are identified by link-local
	address, and icmp6 redirect must be sent with source address set with
	link-local.  for a host to be able to identify its gateway, it needs
	to configure all gateway address by using link-local address.
	this may not be explicitly written, but for a host/router to work
	correctly, it is required.

itojun