said by PhReE5:2601: is the DHCPv6 prefix that is assigned to a router's LAN, but 2001:558: is the prefix for the router's WAN IP address (or I believe for a single PC IP address if no router is involved). Both of those prefixes indicate a native IPv6 address. You are probably thinking of the 2002: prefix that is used for a 6to4 tunnel. said by Arty50:
Thanks for the suggestions. I just ran the test again to confirm. It's native dual stack, not a tunnel. I'm selecting DHCPv6-PD on my router too. No dice.
What type of test? Do you have an ipv6 ip that starts with 2601: or 2001: ? Native IPv6 should be 2601, whereas 2001 is going to be a tunnel.