Description of problem:

• Several nodes reporting NotReady state in two separate occurrences and 4.y.z-streams.
• At a closer look, during the first occurrence, this was seen to be due to a missing "k8s.ovn.org/node-subnets" annotation.
  • A secondary occurrence was showing the same behaviour, this time during the upgrade to 4.18.28, blocking the cluster upgrade.

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

• We've faced this issue twice with the same cluster: initially within 4.17.43 and later during the upgrade to 4.18.28 (this issue is currently blocking the cluster upgrade)

Additional info:

• There are commonalities with the behaviour observed in the the parallel OCPBUGS-66267:
  • The issue is only observed in a cluster within a cluster with Hybrid Overlay enabled (65 other environments without hybrid overlay are not seeing similar behaviors).
  • We're seeing V4SubnetAllocationThresholdExceeded firing in a cluster in a cluster that is well within [0] the clusterNetwork capacity.
    • At a closer look, the ovnkube_clustermanager_allocated_v4_host_subnets on the impacted NotReady [0] nodes  and were reported to reach the ovnkube_clustermanager_num_v4_host_subnets.
    • Restarting the OVN control plane pods restored the value of the ovnkube_clustermanager_allocated_v4_host_subnets, but neither this nor restarting the ovnkube-node pod on the impacted nodes remediated the missing annotation on the nodes.

[0]

$ oc get no --no-headers | wc -l
40
$ oc get no --no-headers | grep "NotReady" | wc -l
13

[1]

2026-01-27T10:20:19.076792681Z I0127 10:20:19.076747  101870 default_node_network_controller.go:779] Waiting for node $NODE to start, no annotation found on node for subnet: could not find "k8s.ovn.org/node-subnets" annotation
2026-01-27T10:20:19.576630275Z I0127 10:20:19.576583  101870 default_node_network_controller.go:779] Waiting for node $NODE to start, no annotation found on node for subnet: could not find "k8s.ovn.org/node-subnets" annotation
2026-01-27T10:20:20.075777353Z I0127 10:20:20.075725  101870 default_node_network_controller.go:779] Waiting for node $NODE to start, no annotation found on node for subnet: could not find "k8s.ovn.org/node-subnets" annotation 

[2]

$ CIDR=`oc get network cluster -o json | jq -r '.spec.clusterNetwork[].cidr'`
$ PFX=`oc get network cluster -o json | jq -r '.spec.clusterNetwork[].hostPrefix'`
$ ipcalc -S $PFX $CIDR

$ ipcalc -S $PFX $CIDR | tail -2
Total:    256
Hosts/Net:  254