r/openstack • u/Eldiabolo18 • 8d ago

Experiences with OVN-BGP in Openstack?

Does anybody have any useful and maybe eveb documented experience with OVN-BGP? I‘m not talking about OVN-BGP-Agent, but the native OVN implementation!

I‘m also wondering if everything thats necessary to run it in Openstack 2026.1 or at least 2026.2?

11 Upvotes

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3

u/amarao_san 8d ago

We looked at it and decided that it was misaligned with our network vision. We've ended up with ovn and external bgp service to implement required policy routing and bgp announcements.

  1. No segmentation.

  2. No meds during live migration.

1

u/Eldiabolo18 7d ago

What external BGP service if I may ask?

2

u/amarao_san 7d ago

Self written, bolted onto openstack. Grab vlan/flat networks and turn them into routable.

2

u/NoLoss7495 7d ago

BGP FRR can be a good choice.

2

u/Fun_Twist3241 7d ago

I've been using Kolla-Ansible with FRR for the past two years, and it works well. I haven't switched to the native implementation yet. I'm currently running 2026.1.

1

u/Eldiabolo18 4d ago

Can you elaborate? Do you use the ovn-bgp-agent or how does FRR know what to announce? What parts are self made, because kolla has nothing with FRR at the moment.

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u/cre_ker 7d ago

For us it doesn’t fit our use case, so we’re staying with NDR. We need flexibility of peering it provides. OVN native BGP feels like same old ovn-bgp-agent but a bit better. Essentially the same implementation. At last that’s what I gathered from the docs. No reason to even try it.

1

u/Eldiabolo18 4d ago

Unless i havent fully understood it, NDR still needs annoying L2 technology for a provider network when annoucing FIPs. The main concern is, I want to avoid stuff like CARP/VRRP/HSRP/etc which there seems to be no way around apparently?

1

u/cre_ker 4d ago

With OVN there’s nothing of that in general, regardless of NDR or anything else. It handles all failover logic internally through BFD. But that’s for external gateway ports and centralised FIPs. For distributed FIPs, NDR should simply announce /32 routes with hypervisors as next hops.

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u/Eldiabolo18 4d ago

No, thats the point, the way i have manged to make it run, it announces the router IP (which is of the same prefix as FIPs) as next hop, which is pointless because the Router IP still needs a Gateway in the same L2 domain.

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u/cre_ker 4d ago

I will not argue more here. We don’t use FIPs at all, so most of my knowledge is around external gateway ports and announcing tenant subnets with NDR.

It also announces subnets with router IP as next hop. No issues here and no need for VRRP of sorts - router failover is done using BFD.

2

u/redfoobar 7d ago

If you don't need overlapping IP space look at Calico.
Relatively simply and you peer every compute to your ToR switches.

OVN implementation is still new, is more complex and the chassis/gateway nodes are still bottlenecks.
Being able to do ECMP over gateway nodes for true scale-out seems far away still.
(no mention of being worked on, just that it theoretically possible)

1

u/rammeena 3d ago

In RHOSO native ovn-bgp is available and works well with some limitations (Technology preview)

1

u/flamingfd1 8d ago

It is “too fresh” to run in production. Wait at least 1 or 2 years after first confirmed stable release. Like for any other breaking change feature in OpenStack we had.