Error 400 while trying to create ext-net (GRE)

Hi

I want to ask about this error
root@network:/home/sysadmin# neutron net-create ext-net --router:external=True --provider:network_type gre --provider:segmentation_id 2
400-{u'NeutronError': {u'message': u'Invalid input for operation: gre networks are not enabled.', u'type': u'InvalidInput', u'detail': u''}}

I have setup an open-stack cloud with 1 controller node, 1 network node and 2 compute nodes. I have followed the official document.
I already setup the all needed plugins on network, controller and compute note
this is the result of #neutron agent-list
+---------------------------------------------------------+------------------------------+----------------+-------+----------------------+
| id | agent_type | host | alive | admin_state_up |
+---------------------------------------------------------+-------------------------- ---+-----------------+-------+----------------------+
| 49c98aaa-52eb-4fdb-8818-fc1cde1c6527 | Open vSwitch agent | compute01 | :-) | True |
| 6caa945c-02dd-4901-bf8f-07b3c3778202 | Open vSwitch agent | network | :-) | True |
| 94f53d9d-c167-40c6-a47a-bf6b56a94e7d | L3 agent | network | :-) | True |
| f3ab084b-ee9b-43f6-b0f2-20e0353af7e1 | Open vSwitch agent | compute02 | :-) | True |
+----------------------------------------------------------+-----------------------------+-----------------+-------+----------------+
I decided to use GRE tunneling.
this is the related content of /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini in Network node
----------------------------------------------------------------------------------------------
[ovs]
# (StrOpt) Type of network to allocate for tenant networks. The
# default value 'local' is useful only for single-box testing and
# provides no connectivity between hosts. You MUST either change this
# to 'vlan' and configure network_vlan_ranges below or change this to
# 'gre' or 'vxlan' and configure tunnel_id_ranges below in order for
# tenant networks to provide connectivity between hosts. Set to 'none'
# to disable creation of tenant networks.

tenant_network_type = gre
tunnel_id_ranges = 1:1000
enable_tunneling = True
integration_bridge = br-int
tunnel_bridge = br-tun
local_ip = 10.0.0.1
---------------------------------------------------------------------------------------------------------
But now when I want to define the ex-net (Create the base Neutron networks) (http://docs.openstack.org/trunk/install-guide/install/apt/content/install-neutron.configure-networks.html) by means of following command I face with bellow error.
is here any body who can help me! I am really confused wit this !
root@network:/home/sysadmin# neutron net-create ext-net --router:external=True --provider:network_type gre --provider:segmentation_id 2
400-{u'NeutronError': {u'message': u'Invalid input for operation: gre networks are not enabled.', u'type': u'InvalidInput', u'detail': u''}}