Then to add IPv6, I just did the following :
$ openstack subnet create --network net_instances --ip-version 6 --ipv6-address-mode=slaac --ipv6-ra-mode=slaac --allocation-pool start=<ipv6start>,end=<ipv6end> --subnet-range <ipv6net>::/64 --gateway <ipv6gateway> subnet_instances_v6
Setup without IPv6 : https:/ /pastebin. ubuntu. com/p/Nqr33HQyg G/
Then to add IPv6, I just did the following : address- mode=slaac --ipv6- ra-mode= slaac --allocation-pool start=< ipv6start> ,end=<ipv6end> --subnet-range <ipv6net>::/64 --gateway <ipv6gateway> subnet_instances_v6
$ openstack subnet create --network net_instances --ip-version 6 --ipv6-
$ openstack router add subnet router_instances subnet_instances_v6
Let me know if you have further questions.
Thanks