diff --git a/include/rabit/io.h b/include/rabit/io.h
index b6b627b7f..307f67f0f 100644
--- a/include/rabit/io.h
+++ b/include/rabit/io.h
@@ -23,6 +23,8 @@ class ISeekStream: public IStream {
   virtual void Seek(size_t pos) = 0;
   /*! \brief tell the position of the stream */
   virtual size_t Tell(void) = 0;
+  /*! \return whether we are at end of file */
+  virtual bool AtEnd(void) const = 0;
 };
 
 /*! \brief fixed size memory buffer */
@@ -55,7 +57,9 @@ struct MemoryFixSizeBuffer : public ISeekStream {
   virtual size_t Tell(void) {
     return curr_ptr_;
   }
-
+  virtual bool AtEnd(void) const {
+    return curr_ptr_ == buffer_size_;
+  }
  private:
   /*! \brief in memory buffer */
   char *p_buffer_;
@@ -95,7 +99,9 @@ struct MemoryBufferStream : public ISeekStream {
   virtual size_t Tell(void) {
     return curr_ptr_;
   }
-
+  virtual bool AtEnd(void) const {
+    return curr_ptr_ == p_buffer_->length();
+  }
  private:
   /*! \brief in memory buffer */
   std::string *p_buffer_;
diff --git a/tracker/rabit_tracker.py b/tracker/rabit_tracker.py
index fe1ec7eb8..244c5fce8 100644
--- a/tracker/rabit_tracker.py
+++ b/tracker/rabit_tracker.py
@@ -134,12 +134,14 @@ class Tracker:
         sock.listen(16)
         self.sock = sock
         self.verbose = verbose
+        if hostIP == 'auto':
+            hostIP = 'dns'
         self.hostIP = hostIP
         self.log_print('start listen on %s:%d' % (socket.gethostname(), self.port), 1)
     def __del__(self):
         self.sock.close()
     def slave_args(self):
-        if self.hostIP == 'auto':
+        if self.hostIP == 'dns':
             host = socket.gethostname()
         elif self.hostIP == 'ip':
             host = socket.gethostbyname(socket.getfqdn())
@@ -261,7 +263,7 @@ class Tracker:
                 wait_conn[rank] = s
         self.log_print('@tracker All nodes finishes job', 2)
 
-def submit(nslave, args, fun_submit, verbose, hostIP):
+def submit(nslave, args, fun_submit, verbose, hostIP = 'auto'):
     master = Tracker(verbose = verbose, hostIP = hostIP)
     submit_thread = Thread(target = fun_submit, args = (nslave, args + master.slave_args()))
     submit_thread.daemon = True