CKA 2026 Scenario 8: Installing Flannel CNI and Fixing Pod-CIDR Mismatch

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A Certified Kubernetes Administrator (CKA) exam scenario presents a cluster where all nodes are in a NotReady state due to the absence of a Container Network Interface (CNI) plugin. Candidates are provided a Flannel manifest and instructed to install a network plugin to restore cluster connectivity. Upon applying the manifest, Flannel pods enter a CrashLoopBackOff state because the manifest's configured network range (10.244.0.0/16) does not match the cluster's actual pod CIDR (192.168.0.0/16). Flannel, which runs as a DaemonSet and reads network settings from a ConfigMap called kube-flannel-cfg, refuses to start when its configured network does not encompass the node's assigned podCIDR. The fix requires updating the net-conf.json Network field in the ConfigMap to align with the cluster's pod CIDR, after which nodes transition to Ready and pod-to-pod communication is restored.

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