This CISSP practice question tests your understanding of cissp exam topics. 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.
Refer to the exhibit. A network administrator configures a new WLAN. Clients can associate but cannot obtain an IP address via DHCP. 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.
The WLAN uses TKIP instead of AES, which is less secure but functional.
Why wrong: TKIP is supported and does not affect DHCP.
B
The WLAN uses WPA2 with PSK, but the passphrase is too short.
Why wrong: The passphrase 'Cisco123' meets minimum length requirements.
C
The broadcast forwarding (or DHCP relay) is not properly configured to forward DHCP requests to the DHCP server.
Without a DHCP relay or server, DHCP broadcasts are not forwarded across the bridge to a DHCP server. The controller needs a DHCP server or a relay configuration.
D
The WLAN interface and the virtual interface are on the same subnet, causing an IP conflict.
Why wrong: They are on the same subnet but different IPs; no conflict unless a device uses both.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The broadcast forwarding (or DHCP relay) is not properly configured to forward DHCP requests to the DHCP server.
The scenario describes that clients can associate but cannot obtain IP addresses via DHCP. This indicates that DHCP broadcast requests from clients are not reaching a DHCP server. The most likely cause is that the bridge group, which connects the WLAN to the wired network, is not configured to forward DHCP broadcasts. Without broadcast forwarding, DHCP discover messages from wireless clients are dropped, preventing lease assignment. Other factors such as encryption type or passphrase length would affect association, not DHCP.
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.
✗
The WLAN uses TKIP instead of AES, which is less secure but functional.
The WLAN uses WPA2 with PSK, but the passphrase is too short.
Why it's wrong here
The passphrase 'Cisco123' meets minimum length requirements.
✓
The broadcast forwarding (or DHCP relay) is not properly configured to forward DHCP requests to the DHCP server.
Why this is correct
Without a DHCP relay or server, DHCP broadcasts are not forwarded across the bridge to a DHCP server. The controller needs a DHCP server or a relay configuration.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The WLAN interface and the virtual interface are on the same subnet, causing an IP conflict.
Why it's wrong here
They are on the same subnet but different IPs; no conflict unless a device uses both.
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.
Trap categories for this question
Keyword trap
The passphrase 'Cisco123' meets minimum length requirements.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Visual reference
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP 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 CISSP subnetting questions on CIDR, address ranges, and subnet selection.
The correct answer is: The broadcast forwarding (or DHCP relay) is not properly configured to forward DHCP requests to the DHCP server. — The scenario describes that clients can associate but cannot obtain IP addresses via DHCP. This indicates that DHCP broadcast requests from clients are not reaching a DHCP server. The most likely cause is that the bridge group, which connects the WLAN to the wired network, is not configured to forward DHCP broadcasts. Without broadcast forwarding, DHCP discover messages from wireless clients are dropped, preventing lease assignment. Other factors such as encryption type or passphrase length would affect association, not DHCP.
What should I do if I get this CISSP 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 CISSP subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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Question Discussion
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