Open Stack

I have external provider network and today when i tried to attached it
to one of DVR router on openstack then it automatically assigned
Provider network gateway IP (10.5.0.1) to DVR router Fixed IP and it
bring down my network :(

How come openstack give external gateway IP (which is not in pool
allocation list) to virtual router?

My allocation pool is 10.5.3.135 to 10.5.3.146  (Gateway is 10.5.0.1)

[root at controller-1 ~(keystone_admin)]# neutron subnet-list
+--------------------------------------+------------------------+------------------+-----------------------------------------------------+
| id                                   | name                   | cidr
            | allocation_pools                                    |
+--------------------------------------+------------------------+------------------+-----------------------------------------------------+
| ca2b3219-52a9-4158-8494-11a7dca72bbb | private_vlan30_subnet1 |
10.5.0.0/21      | {"start": "10.5.3.135", "end": "10.5.3.149"}
|
-------------------------------------------------------------------------------------------------------------


[root at controller-1 ~(keystone_admin)]# neutron subnet-show
ca2b3219-52a9-4158-8494-11a7dca72bbb
+-------------------+----------------------------------------------+
| Field             | Value                                        |
+-------------------+----------------------------------------------+
| allocation_pools  | {"start": "10.5.3.135", "end": "10.5.3.149"} |
| cidr              | 10.5.0.0/21                                  |
| created_at        | 2016-08-26T18:18:45                          |
| description       |                                              |
| dns_nameservers   |                                              |
| enable_dhcp       | False                                        |
| gateway_ip        | 10.5.0.1                                     |
| host_routes       |                                              |
| id                | ca2b3219-52a9-4158-8494-11a7dca72bbb         |
| ip_version        | 4                                            |
| ipv6_address_mode |                                              |
| ipv6_ra_mode      |                                              |
| name              | private_vlan30_subnet1                       |
| network_id        | c9006e25-9496-4cc4-8f1c-4e3fcc6ec0b9         |
| subnetpool_id     |                                              |
| tenant_id         | a7ae274c8f4442c2af7c0a43bc548917             |
| updated_at        | 2016-08-26T18:18:45                          |
+-------------------+----------------------------------------------+