This CKA practice question tests your understanding of troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A pod is running but cannot be accessed via its ClusterIP service from another pod in the same namespace. The service endpoints list shows the pod's IP. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Why wrong: kube-proxy issues would affect all services cluster-wide, not just one service with correct endpoints.
C
The service's targetPort is incorrect
Why wrong: If targetPort were wrong, endpoints might still show but traffic would not reach the container; but endpoints are based on the container port, so if endpoints exist, targetPort matches.
D
The pod is running on a different node without proper routing
Why wrong: ClusterIP services work across nodes; no extra routing needed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A NetworkPolicy is blocking the traffic
Option B is correct because a NetworkPolicy can explicitly deny ingress traffic to a pod even when the service endpoints are correctly populated. Since the endpoints list shows the pod's IP, the service and pod are communicating at the network layer, but a NetworkPolicy with an ingress rule that does not allow traffic from the source pod's labels or CIDR will cause the packet to be dropped by the node's iptables or eBPF rules, resulting in a connection timeout or reset from the client pod.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The kube-proxy is not running on the node
Why it's wrong here
kube-proxy issues would affect all services cluster-wide, not just one service with correct endpoints.
✗
The service's targetPort is incorrect
Why it's wrong here
If targetPort were wrong, endpoints might still show but traffic would not reach the container; but endpoints are based on the container port, so if endpoints exist, targetPort matches.
✗
The pod is running on a different node without proper routing
Why it's wrong here
ClusterIP services work across nodes; no extra routing needed.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The CKA exam frequently reuses these exact scenarios with slightly different constraints.
✓A NetworkPolicy is blocking the trafficCorrect answer▾✗The kube-proxy is not running on the nodeWrong answer — click to see why▾
Why this is wrong here
kube-proxy issues would affect all services cluster-wide, not just one service with correct endpoints.
✗The service's targetPort is incorrectWrong answer — click to see why▾
Why this is wrong here
If targetPort were wrong, endpoints might still show but traffic would not reach the container; but endpoints are based on the container port, so if endpoints exist, targetPort matches.
✗The pod is running on a different node without proper routingWrong answer — click to see why▾
Why this is wrong here
ClusterIP services work across nodes; no extra routing needed.
Analysis generated from the official CKAblueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a populated endpoints list guarantees connectivity, but they overlook that NetworkPolicies operate at a lower layer (L3/L4) and can block traffic even when the service and pod are correctly configured.
Trap categories for this question
Command / output trap
If targetPort were wrong, endpoints might still show but traffic would not reach the container; but endpoints are based on the container port, so if endpoints exist, targetPort matches.
Detailed technical explanation
How to think about this question
NetworkPolicies are implemented by the CNI plugin (e.g., Calico uses iptables or eBPF, Cilium uses eBPF) and are evaluated at the node level before the packet reaches the destination pod. A common subtlety is that NetworkPolicies are namespace-scoped and default-deny if any policy selects the pod; if no ingress rule matches the source pod's labels, the traffic is silently dropped. In a real-world scenario, a developer might see 'curl: (28) Connection timed out' from a client pod, while 'kubectl get endpoints' shows the correct IP, leading them to suspect kube-proxy or routing issues when the actual cause is a restrictive NetworkPolicy.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKA question in full detail.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A NetworkPolicy is blocking the traffic — Option B is correct because a NetworkPolicy can explicitly deny ingress traffic to a pod even when the service endpoints are correctly populated. Since the endpoints list shows the pod's IP, the service and pod are communicating at the network layer, but a NetworkPolicy with an ingress rule that does not allow traffic from the source pod's labels or CIDR will cause the packet to be dropped by the node's iptables or eBPF rules, resulting in a connection timeout or reset from the client pod.
What should I do if I get this CKA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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