openstack 不能访问外网

按官方文档进行安装
http://docs.openstack.org/havana/install-guide/install/yum/content/nova-network.html

不过只有一个网卡。
配置如下
network_manager = nova.network.manager.FlatDHCPManager
firewall_driver = nova.virt.libvirt.firewall.IptablesFirewallDriver
network_size = 254
allow_same_net_traffic = False
multi_host = True
send_arp_for_ha = True
share_dhcp_address = True
force_dhcp_release = True
flat_interface = eth0
flat_network_bridge = br100
public_interface = eth0

启动实例后，在计算节点与虚拟机可以通信，虚拟机不能访问外网
外部了ping不到网桥 11.0.0.1

[root@controller ~]# ifconfig
br100     Link encap:Ethernet  HWaddr 00:50:56:99:2F:62
          inet addr:11.0.0.1  Bcast:11.0.0.255  Mask:255.255.255.0
          inet6 addr: fe80::8819:c4ff:fe6f:a026/64 Scope:Link
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:7481 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2143 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:514926 (502.8 KiB)  TX bytes:217497 (212.3 KiB)

eth0      Link encap:Ethernet  HWaddr 00:50:56:99:2F:62
          inet6 addr: fe80::250:56ff:fe99:2f62/64 Scope:Link
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:8724 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2503 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:702225 (685.7 KiB)  TX bytes:257402 (251.3 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:18435 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18435 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:5017823 (4.7 MiB)  TX bytes:5017823 (4.7 MiB)

virbr0    Link encap:Ethernet  HWaddr 52:54:00:F4:43:99
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

vnet0     Link encap:Ethernet  HWaddr FE:16:3E:37:76:57
          inet6 addr: fe80::fc16:3eff:fe37:7657/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:436 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5964 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:60367 (58.9 KiB)  TX bytes:472516 (461.4 KiB)

有哪位大哥知道哪里出错的么

补充：云计算 ,  OpenStack