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Hi James,
Thanks for the explaination. How can i verify the existence of that
bridge?  Is br-ex that bridge as this is the only bridge that connects to
external network interface? How can i view the namespace of the virtual
router which is responsible for the arp replies?
Thanks,
Akshay

On Sat, Jan 16, 2016 at 3:16 AM, James Denton <james.denton at rackspace.com>
wrote:

> Hi Akshay,
>
> In most cases, you won’t have IP addresses configured on interfaces used
> by Neutron.
>
> The Neutron L2 agents set up or configure the virtual bridges/switches on
> the host based on the type of network in use (VLAN, FLAT, VXLAN, etc). In
> many cases, an external provider network may be setup as a VLAN network. In
> that case, the VLAN ID must correspond to the VLAN configured on the
> physical switch that corresponds to your external network connected to the
> external router. The Neutron virtual router will connect to a virtual
> switch/bridge that effectively “bridges” the virtual network with the
> physical network. When that happens, your physical router and your virtual
> router will be in the same Layer 2 broadcast domain and Layer 3 network.
> Thus, when you have floating IPs configured,they would come from the
> ‘external’ network/pool and your physical router would send ARP requests
> for those addresses. The virtual router would send ARP replies and the
> traffic would be forwarded and NAT’d accordingly.
>
> Of course, all of this working depends on Neutron having been configured
> appropriately and the networks created with the proper provider attribute
> values.
>
> Hope that helps,
>
> James
>
>
> From: Akshay Kumar Sanghai <akshaykumarsanghai at gmail.com>
> Date: Friday, January 15, 2016 at 3:13 PM
> To: "openstack at lists.openstack.org" <openstack at lists.openstack.org>
> Subject: [Openstack] [openstack][neutron]external network packets to
> network node
>
> Hi,
> I have done a kilo ubuntu installation of openstack. One thing i noticed
> was the network node's external interface is unnumbered. Then how does the
> external router forwards the packet to the network node? Suppose a vm has a
> floating ip . I send a packet to that vm using the floating ip. The nat
> happens at the network node. How does the packet reached the network node
> as there is no ip assigned to the interface. I have not configured dvr and
> l3 agent is running on network node.
>
> Thanks,
> Akshay
>
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