[IPv6] Router Gets IPv6 IP and DNS but no Default Gateway tl;dr - Motorola SB6121 + Cicso E3200 Router gets IPv6 IP address and DNS Servers but no Default Gateway.
The whole story:
So, I recently moved a couple miles away and transferred my Comcast service.
At my previous house I had a leased UBee DDM3513 modem with a Cisco/Linksys E3200 router. I had fully functional native dual-stack IPv6 connectivity.
At the new house, the tech swapped the UBee for a Cisco DPC3000 that does not support IPv6 during some troubleshooting. I asked for a v6 modem but he said that was all he had on his truck.
I fixed this by purchasing my own v6 compatible Motorola SB6121 to replace the non-v6 Cisco, and eliminate the monthly rental fee. The modem activated just fine, but I can't get IPv6 working. My E3200 router receives an IP Address (2601: ...) and DNS servers on the v6 side, but it shows 0:0:0:0:0:0:0:0 for the Default Gateway, like its not getting one.
IPv4 works fine. Any ideas why I'm getting an IP and DNS but no Default Gateway when I enable IPv6 on my Cisco E3200 router?