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It is totally normal to write a node subscribing to data published from a bag. For your case, I suggest you do the following steps to make sure you have the correct set up:

1. Play the bag on the 1st machine (where ROS MASTER is running), assuming the scan topic has the name of base_scan
2. In the 2nd machine, dont run your node just yet. Run the following command to make sure the 2nd machine can receive the messages from the 1st machine: rostopic echo /base_scan. If you don't see any data after running this command, that means something wrong with your multi-machine setup. I suggest you fix this by following http://wiki.ros.org/ROS/NetworkSetup
3. Run your node. If you use roslaunch, do remember to add output="screen" flag.