CCNA Network Services and Security Practice Question
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?
⚠ Common exam trap
Cisco often tests the distinction between the DHCP pool's network statement (which defines the range of assignable addresses) and the need to explicitly exclude addresses that are already in use, leading candidates to overlook the ip dhcp excluded-address command and instead focus on unrelated features like conflict logging or lease timers.
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 most likely cause is that the DHCP pool configuration does not exclude the router's own interface IP address (192.168.10.1) from the range of addresses that the DHCP server can assign. By default, a Cisco router acting as a DHCP server will lease any address within the configured network statement unless an explicit ip dhcp excluded-address command is applied. Since the router's interface already uses 192.168.10.1, leasing that same address to a client creates a duplicate IP conflict.
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.
- ✗
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?”
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Related to this question
Learn chapter
Device File Management with SFTP and SCP
Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
Key term
DHCP
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and network settings to devices on a network, so they can communicate without manual configuration.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.