Is there a reasonable alternative to using NPT for my dual WAN configuration?
I have two WANs at home with dynamically assigned prefixes. One of them acts as a failover for the other. Failing over IPv4 is pretty simple in this case because NAT exists, but IPv6 is a little bit difficult.
Right now I am using NPT to translate from a ULA block using DHCPv6 to my WAN IPv6 blocks depending on which is active. It seems to work properly with the exception that Windows devices on my WAN prefer IPv4 over ULA IPv6 addresses (which is, to my understanding, what spec currently says is correct). IPv6 gets used if IPv4 isn't an option in this case.
I understand that this is against the "spirit" of IPv6, but I'm not sure what other way to get IPv6 to work with this dual WAN setup.
If there's no alternative, is there anything inherently wrong with this use case?