Comment 10 for bug 1888256

I make the network with this commands:

openstack network create Flat1 --share --provider-network-type vlan --provider-physical-network vltrunk --provider-segment 719

openstack subnet create \
--gateway 193.224.218.254 \
--subnet-range 193.224.218.0/24 \
--allocation-pool start=193.224.218.1,end=193.224.218.250 \
--host-route destination=169.254.169.254/32,gateway=193.224.218.251 \
--dns-nameserver 193.224.161.70 --dns-nameserver 193.224.161.86 \
--network Flat1 Flat1-subnet-v4

openstack subnet create \
--subnet-range 2001:738:0:527::/64 \
--ip-version 6 --ipv6-address-mode slaac \
--network Flat1 Flat1-subnet-v6

openstack router create Flat1-Router

openstack port create --network Flat1 --fixed-ip ip-address=193.224.218.251 flat1-rtr-port

openstack router add port Flat1-Router flat1-rtr-port

So I not plug any v6 subnet or port to the router, however in Horizon, I can see an IPv6 address assigned with every port in this network (flat1-rtr-port, DHCP ports, etc)
Printscreen here: https://drive.kifu.niif.hu/index.php/s/y5DrkLyP7TcoLps