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

Mike Spreitzer mspreitz at us.ibm.com
Sat Apr 25 20:28:13 UTC 2015

> From: Uwe Sauter <uwe.sauter.de at gmail.com>
> Or instead of using Linux bridges you could use a manually created 
> OpenVSwitch bridge. This allows you to add "internal"
> ports that could be used by Neutron like any other interface.
> - Create OVS bridge
> - Add your external interface to OVS bridge
>   * If your external connection supports/needs VLANs, configure 
> external interface as trunk
> - Add any number of internal interfaces to OVS bridge
>   * Tag each interface with its VLAN ID, if needed
> - Configure Neutron to use one internal interface for each subnet 
> you'd like to use (no VLAN configuration required as
> this happenes outside of Neutron)
> Regards,
>    Uwe
> Am 25.04.2015 um 21:41 schrieb George Shuklin:
> > Can you put them to different vlans? After that it would be very easy 
> > 
> > If not, AFAIK, neutron does not allow this.
> > 
> > Or you can trick it thinking it is (are) separate networks.
> > 
> > Create brige (br-join), plug eth to it.
> > Create to fake external bridges (br-ex1, br-ex2). Join them 
> together to br-join by patch links
> > (http://blog.scottlowe.org/2012/11/27/connecting-ovs-bridges-with-
> patch-ports/)
> > 
> > Instruct neutron like there is two external networks: one on br-
> ex1, second on br-ex2.
> > 
> > But be alert that this not very stable configuration, you need to 
> maintain it by yourself.
> > 
> > On 04/25/2015 10:13 PM, Mike Spreitzer wrote:
> >> Is there a way to create multiple external networks from 
> Neutron's point of view, where both of those networks are
> >> accessed through the same host NIC?  Obviously those networks 
> would be using different subnets.  I need this sort of
> >> thing because the two subnets are treated differently by the 
> stuff outside of OpenStack, so I need a way that a tenant
> >> can get a floating IP of the sort he wants.  Since Neutron 
> equates floating IP allocation pools with external
> >> networks, I need two external networks.
> >>
> >> I found, for example, http://www.marcoberube.com/archives/248--- 
> which describes how to have multiple external
> >> networks but uses a distinct host network interface for each one.
> >>
> >> Thanks,
> >> Mike

Thanks Uwe, I might try that, it sounds like the simplest thing that will 
work.  I think I can not use VLAN tagging in my environment.  I am using 
ML2 with OVS, and it is working now with a single external network. Should 
I expect to find a bridge_mappings entry in my plugin.ini?  I do not find 
one now.  This setup was mainly created by other people, so I am not sure 
what to expect.  When using ML2 with OVS, how do I tell Neutron what my 
bridge mappings are?


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