Normally 6in4 won't work with CGN.
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Yesterday I applied for a HE IPv6 tunnel, and got one. The default tunnel consists of an IPv6 address, ending on ::2, and a routed /64 subnet. What struck me is that the address is in a different /48 subnet than the routed /64 subnet. That means that a whole /48 subnet is burned just to provide my router an IPv6 address.