Turn off temp addresses. If your prefix changes then use ULA addresses.
I suppose I could have said how.
Windows in powershell:
SetNetIPv6Protocol -UseTemporaryAddresses Disabled SetNetIPv6Protocol -RandomizeIdentifiers Disabled
sysctl net.ipv6.conf.all.use_tempaddr=0
ip6-privacy=0
ifconfig em0 inet6 -temporary
Yeah. ULA and nat66 would work nicely. Except you would get murdered for asking about nat66.
I suppose I could have said how.
Windows in powershell:
Linux: or in NetworkManager config file: OpenBSD: