Issue when creating Layer3 CUDN CR as per mentioned in documentation:

apiVersion: k8s.ovn.org/v1
kind: ClusterUserDefinedNetwork
metadata:
  name: <cudn_name> 
spec:
  namespaceSelector: 
    matchExpressions: 
    - key: kubernetes.io/metadata.name 
      operator: In 
      values: ["<example_namespace_one>", "<example_namespace_two>"] 
  network: 
    topology: Layer3 
    layer3: 
      role: Primary 
      subnets: 
        - cidr: 10.100.0.0/16
          hostSubnet: 24

    4.18

Apply below yaml with namespaces:

apiVersion: k8s.ovn.org/v1
kind: ClusterUserDefinedNetwork
metadata:
  name: test-l3 
spec:
  namespaceSelector: 
    matchExpressions: 
    - key: kubernetes.io/metadata.name 
      operator: In 
      values: ["cudn-ns-1", "cudn-ns-2"] 
  network: 
    topology: Layer3 
    layer3: 
      role: Primary 
      subnets: 
        - cidr: 10.100.0.0/16
  

  1. Document correction is needed for CUDN L3 CR.

Apply below yaml with namespaces:   

apiVersion: k8s.ovn.org/v1
kind: ClusterUserDefinedNetwork
metadata:
  name: test-l3 
spec:
  namespaceSelector: 
    matchExpressions: 
    - key: kubernetes.io/metadata.name 
      operator: In 
      values: ["cudn-ns-1", "cudn-ns-2"] 
  network: 
    topology: Layer3 
    layer3: 
      role: Primary 
      subnets: 
        - cidr: 10.100.0.0/16

    L3 CUDN CR must get created fine.

Documentation must be correct as when I tried below yaml it worked for me:

apiVersion: k8s.ovn.org/v1
kind: ClusterUserDefinedNetwork
metadata:
  name: cudn-l3
spec:
  namespaceSelector: 
    matchExpressions: 
    - key: kubernetes.io/metadata.name
      operator: In 
      values: 
      - cudn-ns-1
      - cudn-ns-2
  network: 
    topology: Layer3 
    layer3: 
      role: Primary 
      subnets: 
        - cidr: 10.100.0.0/16

Documentaion link: https://docs.openshift.com/container-platform/4.18/networking/multiple_networks/primary_networks/about-user-defined-networks.html#:~:text=Create%20a%20YAML%20file%2C%20such%20as%20cluster%2Dlayer%2Dthree%2Dudn.yaml%2C%20to%20define%20your%20request%20for%20a%20Layer3%20topology%20as%20in%20the%20following%20example%3A