Description of problem:
the cluster is built with PR https://github.com/openshift/api/pull/1988
4.17.0-0.ci.test-2024-08-05-015438-ci-ln-c2zspkk-latest

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

How reproducible:
Always
Steps to Reproduce:

1. Create namespace ns1 and create NAD in ns1

% oc get net-attach-def -n ns1 -o yaml
apiVersion: v1
items:
- apiVersion: k8s.cni.cncf.io/v1
  kind: NetworkAttachmentDefinition
  metadata:
    creationTimestamp: "2024-08-05T07:00:11Z"
    generation: 1
    name: l3-network-ns1
    namespace: ns1
    resourceVersion: "116820"
    uid: c7a1cce1-59ce-4187-8fba-d725de7f6fd4
  spec:
    config: |
      {
              "cniVersion": "0.3.1",
              "name": "l3-network-ns1",
              "type": "ovn-k8s-cni-overlay",
              "topology":"layer3",
              "subnets": "10.200.0.0/24",
              "mtu": 1300,
              "netAttachDefName": "ns1/l3-network-ns1",
              "role": "primary"
      }
kind: List
metadata:
  resourceVersion: ""

2. Create pods in ns1

% oc get pods -n ns1
NAME            READY   STATUS    RESTARTS   AGE
test-rc-gqz4p   1/1     Running   0          5m17s
test-rc-vdqtb   1/1     Running   0          5m17s
% oc exec -n ns1 test-rc-gqz4p    -- ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0@if49: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1360 qdisc noqueue state UP group default 
    link/ether 0a:58:0a:81:02:1f brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.129.2.31/23 brd 10.129.3.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::858:aff:fe81:21f/64 scope link 
       valid_lft forever preferred_lft forever

3. If use subnet as 10.200.0.0/16, the ovn-udn1 interface will be added, below is configure with this subnet in ns2

 % oc get net-attach-def -n ns2 -o yaml
apiVersion: v1
items:
- apiVersion: k8s.cni.cncf.io/v1
  kind: NetworkAttachmentDefinition
  metadata:
    creationTimestamp: "2024-08-05T07:05:21Z"
    generation: 1
    name: l3-network-ns2
    namespace: ns2
    resourceVersion: "118745"
    uid: f14db678-f74f-4ace-b606-786dfa16c3ce
  spec:
    config: |
      {
              "cniVersion": "0.3.1",
              "name": "l3-network-ns2",
              "type": "ovn-k8s-cni-overlay",
              "topology":"layer3",
              "subnets": "10.200.0.0/16",
              "mtu": 1300,
              "netAttachDefName": "ns2/l3-network-ns2",
              "role": "primary"
      }
kind: List
metadata:

% oc exec -n ns2 test-rc-7f8tq    -- ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0@if57: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1360 qdisc noqueue state UP group default 
    link/ether 0a:58:0a:80:02:26 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.128.2.38/23 brd 10.128.3.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::858:aff:fe80:226/64 scope link 
       valid_lft forever preferred_lft forever
3: ovn-udn1@if58: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1300 qdisc noqueue state UP group default 
    link/ether 0a:58:0a:c8:00:03 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.200.0.3/24 brd 10.200.0.255 scope global ovn-udn1
       valid_lft forever preferred_lft forever
    inet6 fe80::858:aff:fec8:3/64 scope link 
       valid_lft forever preferred_lft forever

Actual results:
No ovn-udn1 interface added when configure the NAD subnets as prefix /24

Expected results:
Should be able to have ovn-udn1 interface. If this subnets configure is not supported, then should give warning when creating the NAD.

Additional info:

Please fill in the following template while reporting a bug and provide as much relevant information as possible. Doing so will give us the best chance to find a prompt resolution.

Affected Platforms:

Is it an

1. internal CI failure
2. customer issue / SD
3. internal RedHat testing failure

If it is an internal RedHat testing failure:

• Please share a kubeconfig or creds to a live cluster for the assignee to debug/troubleshoot along with reproducer steps (specially if it's a telco use case like ICNI, secondary bridges or BM+kubevirt).

If it is a CI failure:

• Did it happen in different CI lanes? If so please provide links to multiple failures with the same error instance
• Did it happen in both sdn and ovn jobs? If so please provide links to multiple failures with the same error instance
• Did it happen in other platforms (e.g. aws, azure, gcp, baremetal etc) ? If so please provide links to multiple failures with the same error instance
• When did the failure start happening? Please provide the UTC timestamp of the networking outage window from a sample failure run
• If it's a connectivity issue,
• What is the srcNode, srcIP and srcNamespace and srcPodName?
• What is the dstNode, dstIP and dstNamespace and dstPodName?
• What is the traffic path? (examples: pod2pod? pod2external?, pod2svc? pod2Node? etc)

If it is a customer / SD issue:

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• Describe what each relevant attachment is intended to demonstrate (failed pods, log errors, OVS issues, etc).
• Referring to the attached must-gather, sosreport or other attachment, please provide the following details:
  • If the issue is in a customer namespace then provide a namespace inspect.
  • If it is a connectivity issue:
    • What is the srcNode, srcNamespace, srcPodName and srcPodIP?
    • What is the dstNode, dstNamespace, dstPodName and dstPodIP?
    • What is the traffic path? (examples: pod2pod? pod2external?, pod2svc? pod2Node? etc)
    • Please provide the UTC timestamp networking outage window from must-gather
    • Please provide tcpdump pcaps taken during the outage filtered based on the above provided src/dst IPs
  • If it is not a connectivity issue:
    • Describe the steps taken so far to analyze the logs from networking components (cluster-network-operator, OVNK, SDN, openvswitch, ovs-configure etc) and the actual component where the issue was seen based on the attached must-gather. Please attach snippets of relevant logs around the window when problem has happened if any.

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