Hi,
I have a CCR2004-16G-2S+ running RouterOS 7.14.2 in my homelab. I’d like to set up a backup link using a FRITZ!Box 6820 LTE router. I have this setup working for IPv4. Despite this creating a triple-NAT situation (MT → Fritzbox → ISP CGNAT), it works fine and is acceptable for a backup link.
However, the challenge with IPv6 is that the ISP (Deutsche Telekom) only provides a /64 prefix on the LTE link. I have configured the Fritzbox to perform IA_PD and IA_NA, but as expected, I only get the address on the MT’s interface since it’s a /64.
I’m exploring if there’s a way for the MT to act as a relay, allowing clients in at least one of my subnets to receive GUAs from the LTE link.
The alternative would be ULAs + NAT, but I’ve read that this solution is suboptimal for various reasons.
Assuming I can get the above working, the next challenge is ensuring clients only use the backup prefix if the main link is down. It’s unclear to me how to control this. Is there a way to only advertise the LTE router’s prefix when the main WAN connection is down?
Would love to hear some thoughts!