- A
The router's ip helper-address command is pointing to an incorrect DHCP server IP address.
Why wrong: The scenario explicitly states that the helper address 10.1.2.5 is configured and points to the remote DHCP server; there is no indication of a misconfiguration.
- B
The switch port connecting to the router is not configured as a trusted port for DHCP snooping.
DHCP snooping trusts only designated ports to forward DHCP server messages. Since the router relays the DHCPOFFER onto the trunk port, an untrusted port will cause the switch to discard the offer, resulting in DHCP failure.
- C
The DHCP server is on a different subnet, so the switch needs a switched virtual interface (SVI) in VLAN 10 with an IP address for Layer 3 connectivity.
Why wrong: DHCP relay is performed by the router, not the switch. The switch does not need an SVI in the client VLAN because the router's subinterface (or routed port) handles inter-VLAN forwarding. The DHCP messages are already routed by the relay agent.
- D
DHCP snooping is dropping DHCPDISCOVER messages because the client access ports are untrusted.
Why wrong: By design, DHCP snooping permits clients to send DHCPDISCOVER and DHCPREQUEST messages on untrusted ports. It only blocks DHCP server–sourced messages (OFFER, ACK) on untrusted ports. Therefore, the DISCOVER messages are not being dropped.
Quick Answer
The answer is that the switch port connecting to the router is not configured as a DHCP snooping trusted port. When DHCP snooping is enabled, all ports are untrusted by default, meaning the switch will drop any DHCP server messages—such as DHCPOFFER and DHCPACK—received on those ports. In this scenario, the router is acting as a DHCP relay agent, forwarding DHCPOFFERs from the remote server back to the clients in VLAN 10. Because the trunk port linking the router is untrusted, the switch discards those responses, preventing clients from obtaining IP addresses. On the CCNA 200-301 v2 exam, this question tests your understanding of DHCP snooping’s default behavior and the critical distinction between trusted and untrusted ports. A common trap is assuming that a router or relay device is automatically trusted; in reality, you must explicitly configure the port with the ip dhcp snooping trust command. Memory tip: think of the relay as a “trusted messenger”—if the switch doesn’t trust the port, it shoots the messenger, and the DHCP offers never arrive.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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 network engineer has enabled DHCP snooping on a Catalyst switch to prevent rogue DHCP servers. All access ports in VLAN 10 are untrusted. A router attached to a trunk port on the switch acts as the default gateway for VLAN 10 and is configured with the ip helper-address 10.1.2.5, which points to a remote DHCP server. After enabling DHCP snooping, hosts in VLAN 10 cannot obtain IP addresses; packet captures show DHCPDISCOVER messages are sent, but no DHCPOFFER is received. 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 switch port connecting to the router is not configured as a trusted port for DHCP snooping.
DHCP snooping treats all ports as untrusted by default. When a router acting as a DHCP relay is connected to an untrusted trunk port, the switch drops DHCPOFFER messages received from the router because they originate from an untrusted interface. Configuring the trunk port as trusted allows DHCP server responses (OFFER, ACK) to pass through to clients.
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 router's ip helper-address command is pointing to an incorrect DHCP server IP address.
Why it's wrong here
The scenario explicitly states that the helper address 10.1.2.5 is configured and points to the remote DHCP server; there is no indication of a misconfiguration.
- ✓
The switch port connecting to the router is not configured as a trusted port for DHCP snooping.
Why this is correct
DHCP snooping trusts only designated ports to forward DHCP server messages. Since the router relays the DHCPOFFER onto the trunk port, an untrusted port will cause the switch to discard the offer, resulting in DHCP failure.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The DHCP server is on a different subnet, so the switch needs a switched virtual interface (SVI) in VLAN 10 with an IP address for Layer 3 connectivity.
- ✗
DHCP snooping is dropping DHCPDISCOVER messages because the client access ports are untrusted.
Why it's wrong here
By design, DHCP snooping permits clients to send DHCPDISCOVER and DHCPREQUEST messages on untrusted ports. It only blocks DHCP server–sourced messages (OFFER, ACK) on untrusted ports. Therefore, the DISCOVER messages are not being dropped.
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 switch port connecting to the router is not configured as a trusted port for DHCP snooping.Correct answer▾
Why this is correct
DHCP snooping trusts only designated ports to forward DHCP server messages. Since the router relays the DHCPOFFER onto the trunk port, an untrusted port will cause the switch to discard the offer, resulting in DHCP failure.
✗The router's ip helper-address command is pointing to an incorrect DHCP server IP address.Wrong answer — click to see why▾
Why this is wrong here
This distractor exploits the common tendency to blame the helper address configuration first, overlooking the security feature that silently drops the returning DHCPOFFER.
✗The DHCP server is on a different subnet, so the switch needs a switched virtual interface (SVI) in VLAN 10 with an IP address for Layer 3 connectivity.Wrong answer — click to see why▾
Why this is wrong here
This plays on the misconception that a switch requires an IP address on the client VLAN to facilitate DHCP, when in fact the router acting as the relay agent provides Layer 3 connectivity.
✗DHCP snooping is dropping DHCPDISCOVER messages because the client access ports are untrusted.Wrong answer — click to see why▾
Why this is wrong here
This misinterprets DHCP snooping behavior: it assumes all DHCP traffic is filtered on untrusted ports, overlooking the critical distinction that only server-side messages are blocked, not client requests.
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: answer the scenario, not the keyword
Cisco often tests the distinction that DHCP snooping blocks DHCP server messages (OFFER/ACK/NAK) on untrusted ports, not client messages (DISCOVER/REQUEST), leading candidates to incorrectly assume client messages are dropped.
Trap categories for this question
Scenario analysis trap
The scenario explicitly states that the helper address 10.1.2.5 is configured and points to the remote DHCP server; there is no indication of a misconfiguration.
Detailed technical explanation
How to think about this question
DHCP snooping builds a DHCP snooping binding table by monitoring DHCPACK messages on trusted ports. When a DHCPOFFER arrives on an untrusted port, the switch discards it without forwarding to the client. In real-world scenarios, forgetting to trust the uplink port to a DHCP relay agent or legitimate DHCP server is a common misconfiguration that breaks IP address assignment.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The switch port connecting to the router is not configured as a trusted port for DHCP snooping. — DHCP snooping treats all ports as untrusted by default. When a router acting as a DHCP relay is connected to an untrusted trunk port, the switch drops DHCPOFFER messages received from the router because they originate from an untrusted interface. Configuring the trunk port as trusted allows DHCP server responses (OFFER, ACK) to pass through to clients.
What should I do if I get this 200-301 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.
About these practice questions
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Last reviewed: Jun 25, 2026
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