Looks like after resolving of https://bugs.launchpad.net/neutron/+bug/1330826 it's impossible now to connect router to subnet with SLAAC addressing.
Steps to reproduce:
$ neutron net-create netto
$ neutron subnet-create --ip_version 6 --ipv6-address-mode slaac --ipv6-ra-mode slaac netto 2021::/64
$ neutron router-create netrouter
$ neutron router-interface-add {router_id} {subnet_id}
The error is:
Invalid input for operation: IPv6 address 2021::1 can not be directly assigned to a port on subnet 8cc737a7-bac1-4fbc-b03d-dfdac7194c08 with slaac address mode.
** The same behaviour if you set gateway explicitly to fixed IP address like 2022::7:
$ neutron subnet-create --ip_version 6 --gateway 2022::7 --ipv6-address-mode slaac --ipv6-ra-mode slaac netto 2022::/64
$ neutron router-interface-add {router_id} {subnet_id}
Invalid input for operation: IPv6 address 2022::7 can not be directly assigned to a port on subnet f4ebf914-9749-49e4-9498-5c10c7bf9a5d with slaac address mode.
*** The same behaviour if we use dhcpv6-stateless instead of SLAAC.
1. It should be legal possibility to add port with fixed IP to SLAAC/stateless networks.
2. When router add its interface to SLAAC subnet it should receive its own SLAAC address by default, if fixed IP address is not specified explicitly.
Looks like we have more work to do in this area. Neutron allocates a gateway_ip when creating a subnet, in the same time creating allocation_pool for this subnet.
The issue with allowing fixed_ip in SLAAC subnet is that it's not possible to give this address to the VM. But this is not an issue with the gateway_ip in the case of neutron router. So the fix could be
-- create the gateway_ip with eui64, and don't allow --gateway-ip to be specified in the case of slaac subnet.
-- honor it, but check the owner of the IP when testing the ip address. And if the owner is the router, accept it; otherwise, error.
Consider https:/
In any case, allocation pool is not necessary to be maintained for a SLAAC subnet.