Have you configured the jupyter_notebook_config.py file to allow external connections?
By default, Jupyter Notebook only accepts connections from localhost (eg, from the same computer that its running on). By modifying the NotebookApp.allow_origin option from the default ' ' to '*', you allow Jupyter to be accessed externally.
c.NotebookApp.allow_origin = '*' #allow all origins
You'll also need to change the IPs that the notebook will listen on:
c.NotebookApp.ip = '0.0.0.0' # listen on all IPs
Make sure that you uncomment these settings (remove the # at the beginning) after making any modifications. If you don't, they'll be interpreted as comments, and they won't change the behavior of the Jupyter notebook client.
Also see the details in a subsequent answer in this thread.
Documentation on the Jupyter Notebook config file.
