title: Not reachable/healthy Replica Set
body: <p>I am trying to add one more replica set in existing sets and getting problem in reachability.
  What are the reasons when we get <strong>Not reachable/healthy</strong> replica set ?</p>
  
  <pre><code>    "name" : "IP ADDRESS",
      "health" : 0,
      "state" : 8,
      "stateStr" : "(not reachable/healthy)",
      "uptime" : 0,
      "optime" : {
          "t" : 0,
          "i" : 0
      },
      "optimeDate" : ISODate("1970-01-01T00:00:00Z"),
      "lastHeartbeat" : ISODate("2013-06-18T10:52:50Z"),
      "lastHeartbeatRecv" : ISODate("1970-01-01T00:00:00Z"),
      "pingMs" : 0
  </code></pre>