I have MultiWAN on OPNsense. My PC IP is always 192.168.0.12. My router decides which upstream it should go. If I go full IPv6, router should derive double IPv6 from both WANs and if main upstream goes down, stop advertising IPv6 from main upstream. Or stop advertising gateway. I don't know what is the right IPv6 way of doing MultiWAN.
Not only PC may change IP, but also servers. Legacy IPv4 DNS can be extended to IPv6, but that mechanical action is not flexible enough. With IPv6 we need to be able to mass replace IPv6 /64 prefix leaving all suffixes intact. We probably need /64 prefix alias system. Software is not prepared for this. In IPv4 SNAT and DNAT were being these "aliases". If NAT is not an option anymore, then DNS must step in.
For many server software it just not possible to listen on multiple IPv6 address. Last time I tried MySQL, it just could not listen on multiple addresses. I could not make it listen on IPv4 and IPv6, specifying two addresses. MySQL server wanted just one address. This address could be [::], which means all interfaces and all protocols. And Linux implements some stupid hack to accept IPv4 connections to IPv6 socket. And Windows Vista also adopted this brainrot. But this is all wrong. Servers have to learn to listen to multiple IPs. This is normal. And for good IPv6 servers should learn to not only listen on multiple IPs, most wanted multiple IPv6, but also rebind listeners on the fly. If I got disconnected from ISP, reconnected by DHCPv6, and ISP assigned another IPv6 prefix, then DynDNS should update all my zones to new /64 prefix, and all servers in my network should rebind listeners.
Or else we may abandon all that TRUE IPv6 philosophy and do SNAT in DNAT in IPv6 just like in IPv4, but with wider address space. But then again, software (another software) is not quite ready for this. Software is expecting public IPv6 address to be just reachable. And private IPv6 address to be just unreachable.
That's illustrates my point well - the "TRUE IPv6" philosophy is major changes in every network-facing user software.. that's why it has been 20+ years and it's not done yet.
And the justification of "Software is expecting public IPv6 address to be just reachable" is super silly. You have to be crazy in this day-and-age to operate without firewall. Every office, every home network should have "default-deny" policy from the internet. So no, your software should not expect to be reachable even once IPv6 adoption is complete.
I have MultiWAN on OPNsense. My PC IP is always 192.168.0.12. My router decides which upstream it should go. If I go full IPv6, router should derive double IPv6 from both WANs and if main upstream goes down, stop advertising IPv6 from main upstream. Or stop advertising gateway. I don't know what is the right IPv6 way of doing MultiWAN.
Not only PC may change IP, but also servers. Legacy IPv4 DNS can be extended to IPv6, but that mechanical action is not flexible enough. With IPv6 we need to be able to mass replace IPv6 /64 prefix leaving all suffixes intact. We probably need /64 prefix alias system. Software is not prepared for this. In IPv4 SNAT and DNAT were being these "aliases". If NAT is not an option anymore, then DNS must step in.
For many server software it just not possible to listen on multiple IPv6 address. Last time I tried MySQL, it just could not listen on multiple addresses. I could not make it listen on IPv4 and IPv6, specifying two addresses. MySQL server wanted just one address. This address could be [::], which means all interfaces and all protocols. And Linux implements some stupid hack to accept IPv4 connections to IPv6 socket. And Windows Vista also adopted this brainrot. But this is all wrong. Servers have to learn to listen to multiple IPs. This is normal. And for good IPv6 servers should learn to not only listen on multiple IPs, most wanted multiple IPv6, but also rebind listeners on the fly. If I got disconnected from ISP, reconnected by DHCPv6, and ISP assigned another IPv6 prefix, then DynDNS should update all my zones to new /64 prefix, and all servers in my network should rebind listeners.
Or else we may abandon all that TRUE IPv6 philosophy and do SNAT in DNAT in IPv6 just like in IPv4, but with wider address space. But then again, software (another software) is not quite ready for this. Software is expecting public IPv6 address to be just reachable. And private IPv6 address to be just unreachable.