how to capture data from Velodyne32, network setting?

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I'm using ubuntu 13.04 64b with ROS Groovy and I'm trying to use velodyne 32.

I've followed the tutorial [Getting Started with the Velodyne HDL-32E] and rviz is not showing the scenes.

1. sudo ifconfig eth0 192.168.3.100 <-- IP for my PC
2. sudo route add 192.168.18.108 eth0 <-- velodyne IP
3. roslaunch velodyne_pointcloud 32e_points.launch calibration:=/home/vic/32db.yaml
4. rosrun rviz rviz -f velodyne > configure as the tutorial said.

Rviz shows a message: "no tf data. Actual error: Fixed frame [/velodyne] does not exist ".

tcpdump and wireshark has captured no package, so my network is not properly set.

What is wrong in my network configuration? Thanks in advance.

Updated: I fixed a wire inside Velodyne and now everything is fine . But I want to understand the network setting.

If I connect velodyne to my PC, with wireshark I detect ethernet packages from velodyne (.18.108) to broadcast (.3.255).

So, I do step 1 ( sudo ifconfig eth0 192.168.3.100) and my PC should "listen" these packages because it is now the receiver.

If I don't do step2, when I do step3 the /velodyne_points is an active topic (rostopic list) but with no data (rostopic echo /velodyne_points).

So, Why do I need step 2? (sudo route add 192.168.18.108 eth0 ). What does? I think is to say "admit packages from this IP". But, is it not the default option? to admit these?

Thanks in advance.