[Openstack-operators] [neutron] multiple external networks on the same host NIC

Mike Spreitzer mspreitz at us.ibm.com
Mon Apr 27 15:49:55 UTC 2015

> "gustavo panizzo (gfa)" <gfa at zumbi.com.ar> wrote on 04/27/2015 11:23:13 
> > On 2015-04-27 22:59, Mike Spreitzer wrote:
> > > Uwe Sauter <uwe.sauter.de at gmail.com> wrote on 04/27/2015 10:54:15 
> > >>
> > >> What I suggested later on is that you probably don't need any 
> > >> level bridge at all. Just create a second/third external
> > >> network with appropriate CIDR. As long as those networks are
> > >> externally connected to your interface (and thus the bridge) you
> > >> should be good to go.
> > > 
> > > To be precise, are you suggesting that I have just one br-ex, 
> > > to the host NIC as usual, and in my bridge_mappings configuration
> > > statement, map all the external network names to br-ex?
> > 
> > you can only have one flat network per bridge.
> > 
> > i don't know what's your usercase but one i had the need to map 2
> > different public ip address to each vm vnic, i was going to do the
> > double bridge thing but i resolved it using allowed pairs extension. 
> > may work for you
> My use case is that I have two behaviorally different external 
> subnets --- they are treated differently by stuff outside of 
> OpenStack, with consequences that are meaningful to tenants.  Thus, 
> I have two categories of floating IP addresses, depending on which 
> external subnet holds the floating IP address.  The difference is 
> meaningful to tenants.  So I need to enable a tenant to request a 
> floating IP address of a specific category.  Since Neutron equates 
> floating IP address allocation pool with network, I need two 
> external networks. 
> Both of these external subnets are present on the same actual 
> external LAN, thus both are reached through the same host NIC. 
> It looks to me like the allowed mac/IP address pair feature will not
> solve this problem. 

Sorry, I simplified too much.  Here is one other critical detail.  I do 
not really have just two different external subnets.  What I really have 
is two behaviorally different collections of subnets.  I need to make a 
Neutron external network for each of the two collections of external 


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