[openstack-dev] [neutron] What semantics are expected when booting a VM on an external network?

Kevin Benton blak111 at gmail.com
Thu Sep 17 14:45:40 UTC 2015


It's not true for all plugins, but an external network should provide the
same semantics of a normal network. The only difference is that it allows
router gateway interfaces to be attached to it. We want to get rid of as
much special casing as possible for the external network.
On Sep 17, 2015 7:02 AM, "Neil Jerram" <Neil.Jerram at metaswitch.com> wrote:

> Thanks to the interesting 'default network model' thread, I now know
> that Neutron allows booting a VM on an external network. :-)  I didn't
> realize that before!
>
> So, I'm now wondering what connectivity semantics are expected (or even
> specified!) for such VMs, and whether they're the same as - or very
> similar to - the 'routed' networking semantics I've described at [1].
>
> [1]
>
> https://review.openstack.org/#/c/198439/5/doc/source/devref/routed_networks.rst
>
> Specifically I wonder if VM's attached to an external network expect any
> particular L2 characteristics, such as being able to L2 broadcast to
> each other?
>
> By way of context - i.e. why am I asking this?...   The
> networking-calico project [2] provides an implementation of the 'routed'
> semantics at [1], but only if one suspends belief in some of the Neutron
> semantics associated with non-external networks, such as needing a
> virtual router to provide connectivity to the outside world.  (Because
> networking-calico provides that external connectivity without any
> virtual router.)  Therefore we believe that we need to propose some
> enhancement of the Neutron API and data model, so that Neutron can
> describe 'routed' semantics as well as all the traditional ones.  But,
> if what we are doing is semantically equivalent to 'attaching to an
> external network', perhaps no such enhancement is needed...
>
> [2] https://git.openstack.org/cgit/openstack/networking-calico
>
> Many thanks for any input!
>
>     Neil
>
>
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