I recently got a rpi3 and installed Raspbian Jessie Lite and pi-hole. Pi-hole is working correctly for IPv4 and ads are being blocked. However I can't get blocking over IPv6 working correctly. During the install I selected both IPv4 and IPv6 using the defaults. So, for IPv6 it's using fe80::4aca:35a5:583b:121d.
My router is an Archer C9 and in the IPv6 configuration section, when I try to specify the Primary DNS as the address above, I get an error saying "Invalid format." I have options for DHCPv6 or SLAAC and prefix delegation (y/n). There is also a section for LAN, which has options for assigned type (DHCPv6, SLAAC+Stateless DHCP or SLAAC+RDNSS). Also has a place to put address prefix. All this stuff is blank.
IPv6 does work just fine when I specify my ISP as the IPv6 DNS. Also works when I specify Open DNS (2620:0:ccc::2).
I don't understand why I can't use the Pi as the IPv6 DNS, but using something like Open DNS works fine.
Any ideas on what could be wrong?