def update_port(self, context, port_id, port):
        """Updates a port.

        Updates the attributes of a port on the specified Virtual
        Network.
        """

        if 'fixed_ips' in port['port']:
            original = self._get_port(context, port_id)
            added_ips, prev_ips = self._update_ips_for_port(
                context, original['network_id'], port_id,
                original['fixed_ips'], port['port']['fixed_ips'])
            port['port']['fixed_ips'] = prev_ips + added_ips

        port = self._update_resource('port', context, port_id, port)
        return self._make_port_dict(port)