node doesn't send kinect data over network

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I'm trying to run an openni node on one machine (Ubuntu 11.04) and publich the data to the master node, which is on another machine (also Ubuntu 11.04) to view it in rviz there. I believe to have my network set up correctly, as I can ping from one machine to the other, and "rostopic list" on the master node returns the topics published by the openni node on the other machine. My problem is that there is no data coming through - "rostopic echo ..." returns nothing on the master node, and rviz therefore obviously doesn't receive anything either. On the machine running openni (the one supposed to be sending the data) I can view the kinect data just fine. When I check my network traffic with system tools, I see that no data is being sent at all. I also have all firewalls disabled.