"IPv6 Multihoming without Network Address Translation"
Network Address and Port Translation (NAPT) works well for conserving
global addresses and addressing multihoming requirements because an
IPv4 NAPT router implements three functions: source address
selection, next-hop resolution, and (optionally) DNS resolution. For
IPv6 hosts, one approach could be the use of IPv6-to-IPv6 Network
Prefix Translation (NPTv6). However, NAT and NPTv6 should be
avoided, if at all possible, to permit transparent end-to-end
connectivity. In this document, we analyze the use cases of
multihoming. We also describe functional requirements and possible
solutions for multihoming without the use of NAT in IPv6 for hosts
and small IPv6 networks that would otherwise be unable to meet
minimum IPv6-allocation criteria. We conclude that DHCPv6-based
solutions are suitable to solve the multihoming issues described in
this document, but NPTv6 may be required as an intermediate solution.
I just did a quick read but I don't understand how this would help the case of your Gateway ethernet link going down temporarily and switching to Cellular WAN?
The client would still need some smart steering to select the correct route no? Does the gateway invalidate the ethernet address somehow?
But with NAT you don't need to worry about it.
> False.
"IPv6 Multihoming without Network Address Translation"
* https://datatracker.ietf.org/doc/html/rfc7157