[ovs-discuss] [OVN] Multiple localnet ports on a single Logical Switch

Daniel Alvarez Sanchez dalvarez at redhat.com
Wed Mar 4 15:01:22 UTC 2020


Hi all,

I wanted to raise this topic and explain the use case for $subject to see
if it makes sense to implement such feature or anybody comes up with a
better idea.

When the localnet implementation was first introduced in OVN [0], the main
use case was referred to OpenStack provider networks, where an admin wants
to create ports in a pre-existing physical network yet providing control
plane management and other features such as Security Groups (ACLs) via
Neutron.

There's another concept in Neutron called Routed Provider Networks [1]
where an admin can define multiple segments (layer-2 domains) within the
same provider network. Each segment could, for example, represent an edge
site and each site will be mapped to a different physical network. E.g

network1 = { segment1:physnet1, segment2:physnet2, ... }

A possible implementation could be to represent each Neutron segment with a
separate OVN Logical Switch and each of them with a localnet port that is
mapped to its physnet. However, this increases complexity as we break the
1:1 mapping between a Neutron network and an OVN Logical Switch.

As a possible alternative, we could support multiple localnet ports on the
same Logical Switch. In the first place, we can assume that on a particular
hypervisor, we're not going to have ports bound to multiple segments (ie.
on hv1 only ports on segment1 will be present, on hv2 only ports on
segment2 will be present and so on...). This way, ovn-controller can create
the patch-port to the provider bridge based on the local bridge-mappings
configuration on each hypervisor and the rest of the localnet ports will
have no effect.

I think that there's some parts in the code that assumes that no more than
one localnet port per logical switch will be present but I don't know the
complexity and/or implications of supporting this use case.

Any feedback is very much appreciated :)

Thanks,
daniel

[0] https://patchwork.ozlabs.org/patch/514209/
[1]
https://docs.openstack.org/neutron/train/admin/config-routed-networks.html
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