Description of problem:

One of the main use-cases for localnet in OCP is OpenShift Virtualization, where VMs use it to connect directly to the underlay network, with or without VLAN encapsulation. In this scenario, OVN's IPAM ("subnets") is typically not used, as the VM relies on the networks DHCP server or static IP allocation.

Although this configuration works well, is tested by Virtualization QE, documented, and adopted by many customers, it does not seem to be properly handled in the codebase:

• There seem to be no e2e test for subnetless localnet on upstream https://github.com/ovn-org/ovn-kubernetes/blob/master/test/e2e/multihoming.go#L219
• Running in this config produces ERROR logs in OVN control plane

Version-Release number of selected component (if applicable):

4.14+

How reproducible:

Always

Steps to Reproduce:

1. Configure localnet

apiVersion: nmstate.io/v1
kind: NodeNetworkConfigurationPolicy
metadata:
  name: ovs-br1-multiple-networks 
spec:
  nodeSelector:
    node-role.kubernetes.io/worker: '' 
  desiredState:
    interfaces:
    - name: ovs-br1 
      description: |-
        A dedicated OVS bridge with eth1 as a port
        allowing all VLANs and untagged traffic
      type: ovs-bridge
      state: up
      bridge:
        options:
          stp: true
        port:
        - name: bond0 
    ovn:
      bridge-mappings:
      - localnet: localnet-network-282
        bridge: ovs-br1 
        state: present 

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: localnet-network-282
  namespace: default
spec:
  config: |2
    {
            "cniVersion": "0.3.1", 
            "name": "localnet-network-282", 
            "type": "ovn-k8s-cni-overlay", 
            "topology": "localnet",
            "vlanID": 282,
            "netAttachDefName": "default/localnet-network-282" 
    } 

2. Request it from a Pod/VM

Actual results:

The network works as expected, but there is an error log:

oc logs -n openshift-ovn-kubernetes ovnkube-control-plane-6556759887-zjn6t -c ovnkube-cluster-manager
I0725 09:22:52.906720 1 controller.go:220] Controller [cluster-manager network manager]: error found while processing localnet-network-282: [cluster-manager network manager]: failed to create network localnet-network-282: no cluster network controller to manage topology
Expected results:

Logs should be clear. Upstream should cover this scenario to make sure we won't suffer regression.

Additional info:

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Affected Platforms:

This issue affected several customers already and mislead troubleshooting efforts.