title: warning:lib openflow _01 fields ignored due to unspecified prerequisites nw_src nw _dst
body: <p>This question has been asked  previously and I have tried everything given in the answers but still getting the same warning. I am using code in this <a href="http://csie.nqu.edu.tw/smallko/sdn/mySDN.pdf" rel="nofollow">link</a>
  (lab4.py &amp; lab4_controller.py). I am creating a separate file of topology in <code>/mininet/examples</code> and trying to access the switches using pox controller from another terminal but getting the above warning.</p>