Strange ROS network trouble

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I'm trying to connect my linux vm ROS environment with the rosmater running on an other machine via openvpn. I am able to ping the IP of the master machine but ROS is having problems. When I do rostopic list, rosnode list or rosgraph the command blocks and doesn't return anything, not even "Unable to contact master".

The environment variables (IP addresses are correct and ping-able both ways):

ROS_MASTER_URI=http://10.8.0.1:11311
ROS_IP=10.8.0.6

When I publish a message I do get publishing and latching message and when I run a node it does start but it does not receive any message from the nodes from the master machine. It looks like the ROS communication is one directional.