diff --git a/gns3server/modules/dynamips/dynamips_hypervisor.py b/gns3server/modules/dynamips/dynamips_hypervisor.py
index 9af7a908..45e6449b 100644
--- a/gns3server/modules/dynamips/dynamips_hypervisor.py
+++ b/gns3server/modules/dynamips/dynamips_hypervisor.py
@@ -351,7 +351,7 @@ class DynamipsHypervisor(object):
             socket_type = socket.SOCK_STREAM
 
         for port in range(start_port, end_port):
-            if port > end_port:
+            if port + 1 == end_port:
                 raise DynamipsError("Could not find a free port between {0} and {1}".format(start_port, end_port))
             try:
                 if ":" in host:
diff --git a/gns3server/modules/dynamips/nodes/router.py b/gns3server/modules/dynamips/nodes/router.py
index 331c60b8..ab485b36 100644
--- a/gns3server/modules/dynamips/nodes/router.py
+++ b/gns3server/modules/dynamips/nodes/router.py
@@ -103,11 +103,9 @@ class Router(object):
                                                                                   platform=platform,
                                                                                   id=self._id))
 
-            # allocate and check that console and aux ports are unused
-            console_port = (self._hypervisor.baseconsole - 1) + self._id
-            self.console = DynamipsHypervisor.find_unused_port(console_port, console_port + 1, self._hypervisor.host)
-            aux_port = (self._hypervisor.baseaux - 1) + self._id
-            self.aux = DynamipsHypervisor.find_unused_port(aux_port, aux_port + 1, self._hypervisor.host)
+            # get console and aux ports
+            self.console = (self._hypervisor.baseconsole - 1) + self._id
+            self.aux = (self._hypervisor.baseaux - 1) + self._id
 
             # get the default base MAC address
             self._mac_addr = self._hypervisor.send("{platform} get_mac_addr {name}".format(platform=self._platform,
@@ -272,6 +270,19 @@ class Router(object):
         if self.get_status() == "suspended":
             self.resume()
         else:
+
+            if self.console and self.aux:
+                # check that console and aux ports are available
+                try:
+                    DynamipsHypervisor.find_unused_port(self.console, self.console + 1, self._hypervisor.host)
+                except DynamipsError:
+                    raise DynamipsError("console port {} is not available".format(self.console))
+
+                try:
+                    DynamipsHypervisor.find_unused_port(self.aux, self.aux + 1, self._hypervisor.host)
+                except DynamipsError:
+                    raise DynamipsError("aux port {} is not available".format(self.aux))
+
             self._hypervisor.send("vm start {}".format(self._name))
             log.info("router {name} [id={id}] has been started".format(name=self._name, id=self._id))
 
diff --git a/gns3server/modules/iou/iou_device.py b/gns3server/modules/iou/iou_device.py
index 31cb98e9..5d0940fb 100644
--- a/gns3server/modules/iou/iou_device.py
+++ b/gns3server/modules/iou/iou_device.py
@@ -793,7 +793,7 @@ class IOUDevice(object):
             socket_type = socket.SOCK_STREAM
 
         for port in range(start_port, end_port):
-            if port > end_port:
+            if port + 1 == end_port:
                 raise IOUError("Could not find a free port between {0} and {1}".format(start_port, end_port))
             try:
                 if ":" in host: