In this instance I was looking to see if the port Cassandra was running was open as I couldn't connect (it turned out it was only listening on localhost).
If you need to find out the status of a port and what its listening on the following command is pretty handy.
The sample below show the result of looking at whats running on port 9160:
sudo netstat -anltp|grep :9160
tcp 0 0 127.0.0.1:9160 0.0.0.0:* LISTEN 1120/jsvc.exec