title: Add Cassandra 2.1 nodes to a Cassandra 1.2.15 cluster?
body: <p>Is it possible to extend an existing Cassandra 1.2.15 cluster by adding Cassandra 2.1 nodes to it?
  The idea, here, is to be able, via another new software, to access the data produced by the one using 1.2.15.</p>
  
  <p>I haven't yet been able to find the answer on the web.</p>