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While looking at some other problems yesterday [1][2] I stumbled across 
this feature change in Juno [3] which adds a config option 
"allow_duplicate_networks" to the [neutron] group in nova. The default 
value is False, but according to the spec [4] neutron allows this and 
it's just exposing a feature available in neutron via nova when creating 
an instance (create the instance with 2 ports from the same network).

My question then is why do we have a config option to toggle a feature 
that is already supported in neutron and is really just turning a 
failure case into a success case, which is generally considered OK by 
our API change guidelines [5].

I'm wondering if there is anything about this use case that breaks other 
NFV use cases, maybe something with SR-IOV / PCI?  If not, I plan on 
pushing a change to deprecate the option in Kilo and remove it in 
Liberty with the default being to allow the operation.

That's barring getting some tests in Tempest to cover the change which 
were promised in the spec but never showed up in Juno, or Kilo, so you 
know, shame shame shame.

[1] https://bugs.launchpad.net/nova/+bug/1430481
[2] https://bugs.launchpad.net/nova/+bug/1430512
[3] https://review.openstack.org/#/c/98488/
[4] https://review.openstack.org/#/c/97716/
[5] 
https://wiki.openstack.org/wiki/APIChangeGuidelines#Generally_Considered_OK

-- 

Thanks,

Matt Riedemann