How to connect VLP-16 velodyne to indigo?

edit

Under Ubuntu 14.04, indigo, My situation now is:

      sudo ifconfig eth0 192.168.1.77

(in new ternimal)

      roscore

(in new terminal)

      cd ./catkin_ws  
  source devel/setup.bash
  roslaunch velodyne_pontcloud VLP16_points.launch

in new terminal:

 rostopic echo /velodyne_points     However, there is no data printed.
 rostopic echo /velodyne_packets   It is said:"Cannot load message class for [velodyne_msgs/VelodyneScan]. Are your mess ages bulit?"

Whether I powered and connected the lidar to my computer or not, there seems to be no difference in the results above.

I think this means the velodyne lidar wasn't connected to linux OS. Is it true?

Therefore, how to connect VLP-16 velodyne to indigo? How to connect the lidar with my computer through the ethernet? I only need to power the lidar and connect the lidar to my computer by the Ethernet line, and I don't need to do anything else? For example, I need to turn off wifi or change some network settings in my linux system?