A port can have multiple fixed IPs assigned from different subnets. If a FIP is associated with the port, it should be possible to update what fixed IP should the FIP be associated with. When updating the fixed IP the port-id is not sent to the Neutron server:
Example:
openstack --debug floating ip set --port 18fa9d0d-f648-4ad6-a59f-7879ad21160f --fixed-ip 10.0.0.78 172.24.4.79
fails in Neutron server:
openstack.exceptions.BadRequestException: BadRequestException: 400: Client Error for url: http://192.168.121.113:9696/networking/v2.0/floatingips/5b65da16-b2b6-451b-b2a5-4e5b29a12ffd, Bad floatingip request: fixed_ip_address cannot be specified without a port_id.
because the request body doesn't send the port ID:
REQ: curl -g -i -X PUT http://192.168.121.113:9696/networking/v2.0/floatingips/5b65da16-b2b6-451b-b2a5-4e5b29a12ffd -H "Content-Type: application/json" -H "User-Agent: openstacksdk/4.2.0 keystoneauth1/5.9.1 python-requests/2.32.3 CPython/3.10.12" -H "X-Auth-Token: {SHA256}993c237d31c1cfda4cfff84886282cb8ab021eebfe3d5cac5e7127317f694a24" -d '{"floatingip": {"fixed_ip_address": "10.0.0.78"}}'
Compared to an update when changing only the port id that works:
openstack floating ip set --port 7207d782-7b04-4310-bc75-85cd433c33d1 172.24.4.79
REQ: curl -g -i -X PUT http://192.168.121.113:9696/networking/v2.0/floatingips/5b65da16-b2b6-451b-b2a5-4e5b29a12ffd -H "Content-Type: application/json" -H "User-Agent: openstacksdk/4.2.0 keystoneauth1/5.9.1 python-requests/2.32.3 CPython/3.10.12" -H "X-Auth-Token: {SHA256}1557c854ea315e6d33bf5ba502cf5cd2ebf2fe5a0171c305fe69c9e210fd1d10" -d '{"floatingip": {"port_id": "7207d782-7b04-4310-bc75-85cd433c33d1"}}'
