[neutron] Status on BGP support when using OVN in Neutron

Daniel Alvarez Sanchez dalvarez at redhat.com
Wed Dec 9 12:33:09 UTC 2020

Hi all,

On Wed, Dec 9, 2020 at 10:56 AM Thomas Goirand <zigo at debian.org> wrote:

> On 12/8/20 4:12 PM, Tim Sæterøy wrote:
> > Hi,
> >
> > I'm trying to explore BGP support when using OVN in Neutron, but
> > haven't been able to find much info on the topic. According to [1]
> > committed in march 2020, OVN seems to lack similar functionality as is
> > seen in ML2/OVS, but there's no further references:
> >
> >> Currently ML2/OVS supports making a tenant subnet routable via BGP,
> >> and can announce host routes for both floating and fixed IP
> >> addresses.
> >
> > I've tried searching for 'bgp' on Neutrons launchpad for issues tagged
> > with 'ovn', in the 'ovn-org/ovn' repo or on docs.ovn.org, but I'm
> > getting blanks.
> >
> > Does anyone happen to know where OVN stands on this, and especially in
> > the context of Neutron? Or perhaps able to point me in the right
> > direction where I can find out more? Thanks.

Precisely, there is a talk scheduled for today in the OVS/OVN con about
introducing BGP support in OVN [0][1] by Nutanix folks. This is more about
EVPN and advertising /32 (or /128) to the router.

So far, there is nothing specific in Neutron for the ML2/OVN driver.
However, neutron-dynamic-routing project would work for you with ML2/OVN to
advertise tenant networks but advertising FIPs is currently relying on
having 'agent gateway' ports which consume one IP per L3 agent per compute
node. This is something that ML2/OVN doesn't do so currently there's no way
with neutron-dynamic-routing to advertise FIP host routes directly to the
compute node.

Can you describe the use cases that you'd have in mind or you just wanted
to know the current status?

Thanks a lot!

[0] https://www.openvswitch.org/support/ovscon2020/

> >
> > [1]: https://docs.openstack.org/neutron/victoria/ovn/gaps.html
> >
> > --
> > Tim
> Hi,
> As much as I know, there's no upstream (ie: OpenStack without downstream
> modification) for BGP-to-the-host support, appart from the
> non-mainstream callico driver, which I haven't tested.
> However, I have been able to do a kind of "bgp-to-the-rack" where the L2
> networking is limited to segments on a single rack. This can be done
> adding this patch to Neutron:
> https://review.opendev.org/c/openstack/neutron/+/669395
> As you can see, I did a few iteration of this patch, but now, I've been
> told to add more db tests, which I don't have the skills for. I asked
> for more help from the Neutron team, but so far, everyone seems busy.
> However, I did test this, and it works kind of well. :)
> If you wish to help to get this patch going in, please do! :)
> Note that this doesn't use OVN. I have no idea if it would work with OVN
> or not (I never did such a setup, only used plain OVS).
> Now, this doesn't replace a full BGP-to-the-host setup, but hopefully,
> the Neutron team will be able to have this done "soon" (whatever that
> means), as interest for it is growing.
> Cheers,
> Thomas Goirand (zigo)
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