diff --git a/gns3server/compute/dynamips/nodes/router.py b/gns3server/compute/dynamips/nodes/router.py
index e53f6fc6..f3d0bc80 100644
--- a/gns3server/compute/dynamips/nodes/router.py
+++ b/gns3server/compute/dynamips/nodes/router.py
@@ -35,6 +35,8 @@ from ...base_node import BaseNode
 from ..dynamips_error import DynamipsError
 from ..nios.nio_udp import NIOUDP
 
+
+from gns3server.utils.file_watcher import FileWatcher
 from gns3server.utils.asyncio import wait_run_in_executor, monitor_process
 from gns3server.utils.images import md5sum
 
@@ -92,6 +94,7 @@ class Router(BaseNode):
         self._system_id = "FTX0945W0MY"  # processor board ID in IOS
         self._slots = []
         self._ghost_flag = ghost_flag
+        self._memory_watcher = None
 
         if not ghost_flag:
             if not dynamips_id:
@@ -160,6 +163,12 @@ class Router(BaseNode):
 
         return router_info
 
+    def _memory_changed(self, path):
+        """
+        Called when the NVRAM file has changed
+        """
+        asyncio.async(self.save_configs())
+
     @property
     def dynamips_id(self):
         """
@@ -248,6 +257,8 @@ class Router(BaseNode):
             yield from self._hypervisor.send('vm start "{name}"'.format(name=self._name))
             self.status = "started"
             log.info('router "{name}" [{id}] has been started'.format(name=self._name, id=self._id))
+
+            self._memory_watcher = FileWatcher(self._memory_files(), self._memory_changed, strategy='hash', delay=30)
             monitor_process(self._hypervisor.process, self._termination_callback)
 
     @asyncio.coroutine
@@ -278,6 +289,9 @@ class Router(BaseNode):
                 log.warn("Could not stop {}: {}".format(self._name, e))
             self.status = "stopped"
             log.info('Router "{name}" [{id}] has been stopped'.format(name=self._name, id=self._id))
+        if self._memory_watcher:
+            self._memory_watcher.close()
+            self._memory_watcher = None
         yield from self.save_configs()
 
     @asyncio.coroutine
@@ -1599,3 +1613,10 @@ class Router(BaseNode):
         yield from self._hypervisor.send('vm clean_delete "{}"'.format(self._name))
         self._hypervisor.devices.remove(self)
         log.info('Router "{name}" [{id}] has been deleted (including associated files)'.format(name=self._name, id=self._id))
+
+    def _memory_files(self):
+        project_dir = os.path.join(self.project.module_working_directory(self.manager.module_name.lower()))
+        return [
+            os.path.join(project_dir, "{}_i{}_rom".format(self.platform, self.dynamips_id)),
+            os.path.join(project_dir, "{}_i{}_nvram".format(self.platform, self.dynamips_id))
+        ]
diff --git a/gns3server/compute/iou/iou_vm.py b/gns3server/compute/iou/iou_vm.py
index f5ea8937..ab510ef4 100644
--- a/gns3server/compute/iou/iou_vm.py
+++ b/gns3server/compute/iou/iou_vm.py
@@ -503,7 +503,7 @@ class IOUVM(BaseNode):
             # check if there is enough RAM to run
             self.check_available_ram(self.ram)
 
-            self._nvram_watcher = FileWatcher(self._nvram_file(), self._nvram_changed)
+            self._nvram_watcher = FileWatcher(self._nvram_file(), self._nvram_changed, delay=10)
 
             # created a environment variable pointing to the iourc file.
             env = os.environ.copy()
diff --git a/gns3server/utils/file_watcher.py b/gns3server/utils/file_watcher.py
index 2de0f7c1..415c6eb0 100644
--- a/gns3server/utils/file_watcher.py
+++ b/gns3server/utils/file_watcher.py
@@ -15,6 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import zlib
 import asyncio
 import os
 
@@ -22,20 +23,43 @@ import os
 class FileWatcher:
     """
     Watch for file change and call the callback when something happen
+
+    :param paths: A path or a list of file to watch
+    :param delay: Delay between file check (seconds)
+    :param strategy: File change strategy (mtime: modification time, hash: hash compute)
     """
 
-    def __init__(self, path, callback, delay=1):
-        if not isinstance(path, str):
-            path = str(path)
-        self._path = path
+    def __init__(self, paths, callback, delay=1, strategy='mtime'):
+        self._paths = []
+        if not isinstance(paths, list):
+            paths = [paths]
+        for path in paths:
+            if not isinstance(path, str):
+                path = str(path)
+            self._paths.append(path)
+
         self._callback = callback
         self._delay = delay
         self._closed = False
+        self._strategy = strategy
 
-        try:
-            self._mtime = os.stat(path).st_mtime_ns
-        except OSError:
-            self._mtime = None
+        if self._strategy == 'mtime':
+            # Store modification time
+            self._mtime = {}
+            for path in self._paths:
+                try:
+                    self._mtime[path] = os.stat(path).st_mtime_ns
+                except OSError:
+                    self._mtime[path] = None
+        else:
+            # Store hash
+            self._hashed = {}
+            for path in self._paths:
+                try:
+                    # Alder32 is a fast bu insecure hash algorithm
+                    self._hashed[path] = zlib.adler32(open(path, 'rb').read())
+                except OSError:
+                    self._hashed[path] = None
         asyncio.get_event_loop().call_later(self._delay, self._check_config_file_change)
 
     def __del__(self):
@@ -48,15 +72,26 @@ class FileWatcher:
         if self._closed:
             return
         changed = False
-        try:
-            mtime = os.stat(self._path).st_mtime_ns
-            if mtime != self._mtime:
-                changed = True
-                self._mtime = mtime
-        except OSError:
-            self._mtime = None
-        if changed:
-            self._callback(self._path)
+
+        for path in self._paths:
+            if self._strategy == 'mtime':
+                try:
+                    mtime = os.stat(path).st_mtime_ns
+                    if mtime != self._mtime[path]:
+                        changed = True
+                        self._mtime[path] = mtime
+                except OSError:
+                    self._mtime[path] = None
+            else:
+                try:
+                    hashc = zlib.adler32(open(path, 'rb').read())
+                    if hashc != self._hashed[path]:
+                        changed = True
+                        self._hashed[path] = hashc
+                except OSError:
+                    self._hashed[path] = None
+            if changed:
+                self._callback(path)
         asyncio.get_event_loop().call_later(self._delay, self._check_config_file_change)
 
     @property
diff --git a/tests/utils/test_file_watcher.py b/tests/utils/test_file_watcher.py
index 11939d5f..2f07315c 100644
--- a/tests/utils/test_file_watcher.py
+++ b/tests/utils/test_file_watcher.py
@@ -15,6 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import pytest
 import asyncio
 from unittest.mock import MagicMock
 
@@ -22,11 +23,12 @@ from unittest.mock import MagicMock
 from gns3server.utils.file_watcher import FileWatcher
 
 
-def test_file_watcher(async_run, tmpdir):
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher(async_run, tmpdir, strategy):
     file = tmpdir / "test"
     file.write("a")
     callback = MagicMock()
-    fw = FileWatcher(file, callback, delay=0.5)
+    fw = FileWatcher(file, callback, delay=0.5, strategy=strategy)
     async_run(asyncio.sleep(1))
     assert not callback.called
     file.write("b")
@@ -34,12 +36,29 @@ def test_file_watcher(async_run, tmpdir):
     callback.assert_called_with(str(file))
 
 
-def test_file_watcher_not_existing(async_run, tmpdir):
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher_not_existing(async_run, tmpdir, strategy):
     file = tmpdir / "test"
     callback = MagicMock()
-    fw = FileWatcher(file, callback, delay=0.5)
+    fw = FileWatcher(file, callback, delay=0.5, strategy=strategy)
     async_run(asyncio.sleep(1))
     assert not callback.called
     file.write("b")
     async_run(asyncio.sleep(1.5))
     callback.assert_called_with(str(file))
+
+
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher_list(async_run, tmpdir, strategy):
+    file = tmpdir / "test"
+    file.write("a")
+
+    file2 = tmpdir / "test2"
+
+    callback = MagicMock()
+    fw = FileWatcher([file, file2], callback, delay=0.5, strategy=strategy)
+    async_run(asyncio.sleep(1))
+    assert not callback.called
+    file2.write("b")
+    async_run(asyncio.sleep(1.5))
+    callback.assert_called_with(str(file2))