diff --git a/core/src/main/scala/org/apache/spark/SparkEnv.scala b/core/src/main/scala/org/apache/spark/SparkEnv.scala
index 27497e21b829d..2244303bbf420 100644
--- a/core/src/main/scala/org/apache/spark/SparkEnv.scala
+++ b/core/src/main/scala/org/apache/spark/SparkEnv.scala
@@ -235,7 +235,7 @@ object SparkEnv extends Logging {
     // for incoming connections.
     if (isDriver) {
       conf.set("spark.driver.port", rpcEnv.address.port.toString)
-    } else if (rpcEnv.address != null) {
+    } else if (rpcEnv.address.port != -1) {
       conf.set("spark.executor.port", rpcEnv.address.port.toString)
     }
 
diff --git a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
index e08729510926b..e337739640e25 100644
--- a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
+++ b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
@@ -75,9 +75,10 @@ private[spark] class CoarseGrainedExecutorBackend(
   }
 
   override def receive: PartialFunction[Any, Unit] = {
-    case RegisteredExecutor(hostname) =>
+    case RegisteredExecutor =>
       logInfo("Successfully registered with driver")
-      executor = new Executor(executorId, hostname, env, userClassPath, isLocal = false)
+      executor = new Executor(executorId, env.rpcEnv.address.host, env,
+        userClassPath, isLocal = false)
 
     case RegisterExecutorFailed(message) =>
       logError("Slave registration failed: " + message)
diff --git a/core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala b/core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala
index 7f2192e1f5a70..d1ff4f92bc2d3 100644
--- a/core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala
+++ b/core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala
@@ -120,9 +120,15 @@ private[netty] class NettyRpcEnv(
       RpcEndpointVerifier.NAME, new RpcEndpointVerifier(this, dispatcher))
   }
 
-  @Nullable
   override lazy val address: RpcAddress = {
-    if (server != null) RpcAddress(host, server.getPort()) else null
+    // When running in client mode (i.e.: not opening a listening port, but connecting to a
+    // 'server' with an open port), the server value is null.
+    // But a valid host still has to be provided, as it is needed later on.
+    // Previously, the server side of the connection was attempting to guess the client
+    // hostname, using the connection information. But the value generated is wrong when
+    // the connection is NATed.
+    // [SPARK-14849]
+    if (server != null) RpcAddress(host, server.getPort()) else RpcAddress(host, -1)
   }
 
   override def setupEndpoint(name: String, endpoint: RpcEndpoint): RpcEndpointRef = {
@@ -152,8 +158,8 @@ private[netty] class NettyRpcEnv(
     if (receiver.client != null) {
       message.sendWith(receiver.client)
     } else {
-      require(receiver.address != null,
-        "Cannot send message to client endpoint with no listen address.")
+      require(receiver.address.port != -1,
+        "Cannot send message to client endpoint with no listen port.")
       val targetOutbox = {
         val outbox = outboxes.get(receiver.address)
         if (outbox == null) {
diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedClusterMessage.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedClusterMessage.scala
index 46a829114ec86..70341cc8272be 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedClusterMessage.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedClusterMessage.scala
@@ -40,7 +40,7 @@ private[spark] object CoarseGrainedClusterMessages {
 
   sealed trait RegisterExecutorResponse
 
-  case class RegisteredExecutor(hostname: String) extends CoarseGrainedClusterMessage
+  case object RegisteredExecutor extends CoarseGrainedClusterMessage
     with RegisterExecutorResponse
 
   case class RegisterExecutorFailed(message: String) extends CoarseGrainedClusterMessage
diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
index 8896391f9775f..dceb39c66fc0f 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
@@ -153,13 +153,7 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp
           executorRef.send(RegisterExecutorFailed("Duplicate executor ID: " + executorId))
           context.reply(true)
         } else {
-          // If the executor's rpc env is not listening for incoming connections, `hostPort`
-          // will be null, and the client connection should be used to contact the executor.
-          val executorAddress = if (executorRef.address != null) {
-              executorRef.address
-            } else {
-              context.senderAddress
-            }
+          val executorAddress = executorRef.address
           logInfo(s"Registered executor $executorRef ($executorAddress) with ID $executorId")
           addressToExecutorId(executorAddress) = executorId
           totalCoreCount.addAndGet(cores)
@@ -178,7 +172,7 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp
               logDebug(s"Decremented number of pending executors ($numPendingExecutors left)")
             }
           }
-          executorRef.send(RegisteredExecutor(executorAddress.host))
+          executorRef.send(RegisteredExecutor)
           // Note: some tests expect the reply to come after we put the executor in the map
           context.reply(true)
           listenerBus.post(