I have followed the Icehouse doc to install a 3 node environment. All nodes are builded as virtual machines using libvirt in CentOS 6.5

http://docs.openstack.org/icehouse/install-guide/install/yum/content/basics-networking-neutron.html

-controller-node : 10.0.0.11 (management network)
-network-node : 10.0.0.21 (management network)
                10.0.1.21 (data network)
-compute-node : 10.0.0.31 (management network)
                10.0.1.31 (data network)
-external network : 192.168.125.0/24
-demo network : 172.30.1.0/24

In my network node, external NIC is configured witout IP as per the documentation. (PROMISC="yes")

DEVICE="eth1"
TYPE="Ethernet"
ONBOOT="yes"
PROMISC="yes"
BOOTPROTO="none"
HWADDR="52:54:00:D3:92:E2"
UUID="7f8a9e99-fbd0-4c59-900f-2369c9e8f780"

However, even though ARP tables of both sides are no problem, I cannot ping the external network in a below stage.

http://docs.openstack.org/icehouse/install-guide/install/yum/content/neutron_initial-networks-verify.html

① inside(tenant router gateway on network-node) -> outside(external geteway)

[root@network-node ~]# ping 192.168.125.254
PING 192.168.125.254 (192.168.125.254) 56(84) bytes of data.
From 192.168.125.54 icmp_seq=1 Destination Host Unreachable
From 192.168.125.54 icmp_seq=2 Destination Host Unreachable
From 192.168.125.54 icmp_seq=3 Destination Host Unreachable

② outside -> inside

[root@desktop ~]# ping 192.168.125.150
PING 192.168.125.150 (192.168.125.150) 56(84) bytes of data.
--> receive no response

This is the info of my environment:

1) controller node

[root@controller-node]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:91:4e:06 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.11/24 brd 10.0.0.255 scope global eth0
    inet6 fe80::5054:ff:fe91:4e06/64 scope link 
       valid_lft forever preferred_lft forever
[root@controller-node]# 
[root@controller-node]# neutron net-list
+--------------------------------------+----------+-------------------------------------------------------+
| id                                   | name     | subnets                                               |
+--------------------------------------+----------+-------------------------------------------------------+
| 9cebb2a6-fd73-4ef7-81d2-188652f57ecd | demo-net | c66648c9-c34b-4806-af39-3c982378a411 172.30.1.0/24    |
| e5f7b93c-475c-4c9d-95e4-8d1cf7728013 | ext-net  | a1e1fcc6-d596-4959-8923-9b46d64445af 192.168.125.0/24 |
+--------------------------------------+----------+-------------------------------------------------------+
[root@controller-node]# neutron subnet-list
+--------------------------------------+-------------+------------------+--------------------------------------------------------+
| id                                   | name        | cidr             | allocation_pools                                       |
+--------------------------------------+-------------+------------------+--------------------------------------------------------+
| a1e1fcc6-d596-4959-8923-9b46d64445af | ext-subnet  | 192.168.125.0/24 | {"start": "192.168.125.150", "end": "192.168.125.159"} |
| c66648c9-c34b-4806-af39-3c982378a411 | demo-subnet | 172.30.1.0/24    | {"start": "172.30.1.2", "end": "172.30.1.254"}         |
+--------------------------------------+-------------+------------------+--------------------------------------------------------+
[root@controller-node]# 
[root@controller-node]# neutron port-list
+--------------------------------------+------+-------------------+----------------------------------------------------------------------------------------+
| id                                   | name | mac_address       | fixed_ips                                                                              |
+--------------------------------------+------+-------------------+----------------------------------------------------------------------------------------+
| 9810105a-edf5-41bc-a140-81ccf71f6bc4 |      | fa:16:3e:34:fd:cb | {"subnet_id": "a1e1fcc6-d596-4959-8923-9b46d64445af", "ip_address": "192.168.125.150"} |
| 98c762ea-d7f7-4c1d-9b74-73efc9990236 |      | fa:16:3e:cb:0c:11 | {"subnet_id": "c66648c9-c34b-4806-af39-3c982378a411", "ip_address": "172.30.1.1"}      |
| f5eec840-e629-448b-ba9a-fbcd60501247 |      | fa:16:3e:ae:a6:fa | {"subnet_id": "c66648c9-c34b-4806-af39-3c982378a411", "ip_address": "172.30.1.2"}      |
+--------------------------------------+------+-------------------+----------------------------------------------------------------------------------------+
[root@controller-node]# 
[root@controller-node]# neutron router-show demo-router
+-----------------------+-----------------------------------------------------------------------------+
| Field                 | Value                                                                       |
+-----------------------+-----------------------------------------------------------------------------+
| admin_state_up        | True                                                                        |
| external_gateway_info | {"network_id": "e5f7b93c-475c-4c9d-95e4-8d1cf7728013", "enable_snat": true} |
| id                    | 8ae4b1fa-fb60-4690-bbe2-febbfbcf7555                                        |
| name                  | demo-router                                                                 |
| routes                |                                                                             |
| status                | ACTIVE                                                                      |
| tenant_id             | c94f1dc5870a4d06a8b6ba947e1ac554                                            |
+-----------------------+-----------------------------------------------------------------------------+
[root@controller-node]# 
[root@controller-node ...