I was getting the same error and got this to work by using disable_node_auto_discovery!
You can see in the documentation for this method that it says "This is primarily helpful when the cassandra cluster is communicating internally on a different ip address than what you are using to connect. A prime example of this would be when using EC2 to host a cluster. Typically, the cluster would be communicating over the local ip addresses issued by Amazon, but any clients connecting from outside EC2 would need to use the public ip."
http://rdoc.info/github/cassandra-rb/cassandra/master/Cassandra:disable_node_auto_discovery!