    # File lib/fog/xenserver/requests/compute/create_vif.rb, line 21
            def default_vif_config( vm_ref, network_ref, device_number = '-1' )
              conf = {
                'MAC_autogenerated' => 'True',
                'VM' => vm_ref,
                'network' => network_ref,
                'MAC' => '',
                'MTU' => '0',
                'other_config' => {},
                'qos_algorithm_type' => 'ratelimit',
                'qos_algorithm_params' => {}
              }
              if device_number.to_i >= 0
                conf['device'] = device_number
              else
                highest_dev = 0
                server = servers.get vm_ref
                server.vifs.each do |vif|
                  dev = vif.device.to_i
                  highest_dev = dev if dev > highest_dev
                end
                conf['device'] = (highest_dev + 1).to_s
              end
              conf
            end