In order to ensure that the Java driver can connect to a Cassandra or DSE cluster, check the following requirements:

• The cluster is running Apache Cassandra 1.2+ or DSE 3.2+

• In cassandra.yaml you have set:

  start_native_transport: true
  rpc_address: IP or hostname reachable from the client
  

• Machines in the cluster accept connections on port 9042

  Note: the client port can be configured using the native_transport_port in cassandra.yaml.

You can find more details about these settings from cassandra.yaml in Apache Cassandra - The cassandra.yaml configuration file docs