Thanks for the response and also for the link :-)

Actually we are struggling with the floating IP so each one of them matters.

I am thinking to go for a model where I can use minimum floating IPs, can’t 
afford to give a new floating IP to each new tenant's routers.

 Since its not a production environment we can compromise on performance and 
different tenants traffic can share same interface.

Regards..
Salman.

PhD, Scientific Computing
Researcher, IT Department,
Uppsala University.
Cloud Application Expert,
UPPMAX.
Visiting Researcher,
Helsinki Institute of Physics (HIP).
[email protected]<mailto:[email protected]>
http://www.it.uu.se/katalog/salto690

On 02 Sep 2015, at 00:28, James Denton 
<[email protected]<mailto:[email protected]>> wrote:

Hi Salman,

The external bridge, br-ex, does not require an IP address. When routers are 
connected to the bridge, it is true they procure an address from the external 
provider network. The address is applied to the qg interface within the router 
namespace.

When instances send traffic out, the router NATs the traffic using its 
respective IP (known as SNAT, or many to one.) When an instance has a floating 
IP, the router will NAT the traffic using the floating IP instead (known as one 
to one). The SNAT behavior can be disabled on a particular router if necessary, 
but it introduces routing issues that need to be solved upstream.

James

Sent from my iPhone

On Sep 1, 2015, at 4:33 PM, Salman Toor 
<[email protected]<mailto:[email protected]>> wrote:

Hi,

Can some one please explain it a bit or redirect me to the document.

So on neutron node we need external interface br-ex (public IP) and than each 
tenant's router also occupies a real IP when we attach it to external net.

I am wondering what is the path instances traffic take to go out? I mean will 
it go via the public IP attached to the router or its via br-ex?

Regards..
Salman.

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