This CKAD practice question tests your understanding of services and networking. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
An administrator wants to allow ingress traffic to pods with label 'app: database' only from pods with label 'app: api' in the same namespace. Which NetworkPolicy rule is correct?
The ingress rule should select pods with label 'app: database' as the podSelector, and allow from pods with label 'app: api' via a podSelector in the from block. Option A is correct. Option B selects the wrong pods. Option C uses namespaceSelector, which is not needed. Option D uses ipBlock, which is not appropriate.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Incorrect. This allows from any pod in the default namespace, not specifically api pods.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKAD question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CKAD subnetting questions on CIDR, address ranges, and subnet selection.
Services and Networking — This question tests Services and Networking — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: podSelector: { matchLabels: { app: database } }
ingress:
- from:
- podSelector: { matchLabels: { app: api } } — The ingress rule should select pods with label 'app: database' as the podSelector, and allow from pods with label 'app: api' via a podSelector in the from block. Option A is correct. Option B selects the wrong pods. Option C uses namespaceSelector, which is not needed. Option D uses ipBlock, which is not appropriate.
What should I do if I get this CKAD question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CKAD subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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