I configured this router with Google Fiber as the primary WAN and a cellular provider as the backup. Everything is working except IPv6 on the Google Fiber connection.

I am using Dynamic IP (SLAAC/DHCPv6) with DHCPv6 selected, Prefix Delegation enabled and set to 56, and DNS Address set to Get dynamically from ISP.

When I save, I get a warning for about 5 minutes:

WAN: DHCPCv6 Solicit/Discover Timeout.

Then it will show success but only pull the DNS, not the address, and then immediately release. This repeats indefinitely.

WAN: Dynamic IPv6 acquirement succeeded. (IPv6=/64, Gateway= , DNS=2001:4860:4860::8888 2001:4860:4860::8844.)

WAN: DHCPv6 release IPv6 address successfully.

I was previously getting this message when trying with /64 so I believe /56 is correct.

Prefix Delegation Size incompatible with ISP: Dynamic IPv6 acquirement succeeded. (IPv6=, Gateway=, DNS=.)

I have tried multiple MTUs and currently have it set to 1280.

I also contacted Google Fiber and they were unable to provide any information other than the standard 'restart your fiber jack and router' which I did.

Does anyone know what settings would work? I'm in Kansas City if Google Fiber uses different configurations in different regions.