# 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