Comment 4 for bug 1831726

Brian's followup in #3 is correct.

'neutron' CLI just replaces an existing value of fixed_ips with specified information. If a previous IP address is not specified in the command line, the previous IP address will be released and only specified IP address(es) will be assigned.

On the other hand, 'openstack' CLI is designed in more user-friendly way and it supports add/remove operations for a list-type attribute like fixed_ips. The help message of OSC port set command says as follows:

  --fixed-ip subnet=<subnet>,ip-address=<ip-address>
                        Desired IP and/or subnet for this port (name or ID):
                        subnet=<subnet>,ip-address=<ip-address> (repeat option
                        to set multiple fixed IP addresses)
  --no-fixed-ip Clear existing information of fixed IP
                        addresses.Specify both --fixed-ip and --no-fixed-ip to
                        overwrite the current fixed IP addresses.

My current suggestion is to use 'openstack' CLI instead. The upstream development team considers 'openstack' CLI as the first priority (over 'neutron' CLI) now.