- A
The DHCP pool does not exclude the router’s own interface IP address.
When no excluded-address is configured for the router’s IP, the DHCP server treats it as available from the pool and can offer it to clients, creating a conflict. Adding 'ip dhcp excluded-address 192.168.10.1' prevents the server from offering that address.
- B
The DHCP conflict logging feature is disabled on the router.
Why wrong: DHCP conflict detection (logging) only records address conflicts after a lease is offered; it does not prevent the server from offering a conflicting address. Disabling it does not cause the server to hand out the router’s IP.
- C
The DHCP lease time is set too low, causing frequent re-issuing of addresses.
Why wrong: A short lease time simply reduces how long a client keeps an address; it does not influence which addresses the server offers. The router would still offer available pool addresses, including the duplicate, regardless of lease duration.
- D
The DHCP pool’s default-router address is misconfigured, so the client uses the router’s IP as its own.
Why wrong: The default-router option tells the client which IP to use as its default gateway; it does not assign that address to the client’s interface. Even if misconfigured, the client would still be assigned an IP from the pool, and it would use the default-router IP only as a gateway, not as its own address.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 network engineer notices that clients in the 192.168.10.0/24 subnet are receiving the IP address 192.168.10.1 from the DHCP server, causing a duplicate IP conflict with the router’s own interface. 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.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The DHCP pool does not exclude the router’s own interface IP address.
The DHCP server is handing out 192.168.10.1, which is the router’s interface IP, because the pool includes the entire subnet without excluding that address. The correct fix is to configure 'ip dhcp excluded-address 192.168.10.1'. The other options describe features that do not control whether the server offers a specific address: conflict logging, lease time, and default-router settings do not prevent assignment of a duplicate address.
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 DHCP pool does not exclude the router’s own interface IP address.
Why this is correct
When no excluded-address is configured for the router’s IP, the DHCP server treats it as available from the pool and can offer it to clients, creating a conflict. Adding 'ip dhcp excluded-address 192.168.10.1' prevents the server from offering that address.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The DHCP conflict logging feature is disabled on the router.
Why it's wrong here
DHCP conflict detection (logging) only records address conflicts after a lease is offered; it does not prevent the server from offering a conflicting address. Disabling it does not cause the server to hand out the router’s IP.
- ✗
The DHCP lease time is set too low, causing frequent re-issuing of addresses.
Why it's wrong here
A short lease time simply reduces how long a client keeps an address; it does not influence which addresses the server offers. The router would still offer available pool addresses, including the duplicate, regardless of lease duration.
- ✗
The DHCP pool’s default-router address is misconfigured, so the client uses the router’s IP as its own.
Why it's wrong here
The default-router option tells the client which IP to use as its default gateway; it does not assign that address to the client’s interface. Even if misconfigured, the client would still be assigned an IP from the pool, and it would use the default-router IP only as a gateway, not as its own address.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The DHCP pool does not exclude the router’s own interface IP address.Correct answer▾
Why this is correct
When no excluded-address is configured for the router’s IP, the DHCP server treats it as available from the pool and can offer it to clients, creating a conflict. Adding 'ip dhcp excluded-address 192.168.10.1' prevents the server from offering that address.
✗The DHCP conflict logging feature is disabled on the router.Wrong answer — click to see why▾
Why this is wrong here
Many candidates confuse conflict detection with a preventive mechanism, thinking that enabling it would stop the assignment of an already-used address.
✗The DHCP lease time is set too low, causing frequent re-issuing of addresses.Wrong answer — click to see why▾
Why this is wrong here
Candidates may associate short leases with instability, but the root cause is the missing exclusion, not the lease timer.
✗The DHCP pool’s default-router address is misconfigured, so the client uses the router’s IP as its own.Wrong answer — click to see why▾
Why this is wrong here
Beginners often conflate the default gateway with the assigned IP address, believing a mistake in the default-router setting could cause an address conflict.
Analysis generated from the official 200-301blueprint 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: 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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The DHCP pool does not exclude the router’s own interface IP address. — The DHCP server is handing out 192.168.10.1, which is the router’s interface IP, because the pool includes the entire subnet without excluding that address. The correct fix is to configure 'ip dhcp excluded-address 192.168.10.1'. The other options describe features that do not control whether the server offers a specific address: conflict logging, lease time, and default-router settings do not prevent assignment of a duplicate address.
What should I do if I get this 200-301 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 200-301 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.
About these practice questions
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Last reviewed: Jun 14, 2026
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