In specific deployments, e.g., with BGP EVPN configured for OVN logical switches / routers (the BGP control plane is executed outside of OVN), OVN owned IP addresses should be advertised to the fabric (EVPN).

OVN should provide a way for users to configure an OVN logical switch to install (Linux) FDB and ip neigh entries (for all IPs owned by logical switch ports that are bound locally) into the tables of a Linux (VRF) bridge that's used by the control plane (e.g., FRR) to advertise MAC addresses through EVPN.

Notes on potential implementation details:

• OVN already supports dynamic route redistribution - blackhole routes are injected through netlink into the VRF associated to an OVN router that has dynamic route redistribution enabled
• this mechanism could be extended to allow injecting static Linux FDB and IP neigh entries into such VRFs - the control plane (e.g., FRR) would then take care of advertising these mac and IP address mappings through EVPN
• a prerequisite seems to be that a loopback interface must exist (e.g., created by the CMS) and must be attached to the Linux bridge used by FRR for EVPN; static FDB/neigh records must be added using this loopback interface

E.g., simulate the effect of ovn-controller injecting FDB and neigh entries for a MAC and IP on VNI 20:

vni=20
podman exec $h1 ip neigh add dev br-$vni 42.42.1.$vni lladdr 00:01:42:42:00:$vni nud permanent
podman exec $h1 bridge fdb add 00:01:42:42:00:$vni dev lo-$vni master static