Question 855 of 2,152

DHCP (IPv4 and IPv6) →hardMultiple ChoiceObjective-mapped

300-410 DHCP (IPv4 and IPv6) Practice Question

This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). 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 configures a DHCP snooping trusted port on a switch to allow a legitimate DHCP server. However, clients connected to untrusted ports on the same VLAN cannot obtain IP addresses. The DHCP server is reachable and the switch shows no DHCP snooping drops. Which is the most likely explanation?

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.

A
The DHCP server is not configured to trust the relay agent information option (option 82), causing it to discard the requests.
Correct: By default, DHCP snooping inserts option 82. Many servers reject packets with option 82 unless configured to trust it.
B
The trusted port is in the wrong VLAN; DHCP snooping only works when the trusted port is in the same VLAN as the clients.
Why wrong: Incorrect: The trusted port can be in any VLAN; DHCP snooping operates per VLAN.
C
The switch has 'ip dhcp snooping verify mac-address' enabled, causing MAC address mismatches.
Why wrong: Incorrect: This feature checks the source MAC in the DHCP packet against the Ethernet header, but the issue is about option 82.
D
The DHCP server is not configured with the correct subnet for the client VLAN.
Why wrong: Incorrect: This would cause server-side issues, but the symptom is that no clients get addresses, and the server is reachable.

Full breakdown with real-world context →

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 server is not configured to trust the relay agent information option (option 82), causing it to discard the requests.

When DHCP snooping is enabled, the switch inserts the relay agent information option (option 82) into DHCP requests received on untrusted ports. If the DHCP server is not configured to trust or process option 82, it will discard these requests, preventing clients from obtaining IP addresses even though the switch reports no drops. This is the most likely cause because the DHCP server is reachable and the switch shows no drops, indicating the issue lies with how the server handles the relayed packets.

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 DHCP server is not configured to trust the relay agent information option (option 82), causing it to discard the requests.
Why this is correct
Correct: By default, DHCP snooping inserts option 82. Many servers reject packets with option 82 unless configured to trust it.
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 trusted port is in the wrong VLAN; DHCP snooping only works when the trusted port is in the same VLAN as the clients.
Why it's wrong here
Incorrect: The trusted port can be in any VLAN; DHCP snooping operates per VLAN.
✗
The switch has 'ip dhcp snooping verify mac-address' enabled, causing MAC address mismatches.
Why it's wrong here
Incorrect: This feature checks the source MAC in the DHCP packet against the Ethernet header, but the issue is about option 82.
✗
The DHCP server is not configured with the correct subnet for the client VLAN.
Why it's wrong here
Incorrect: This would cause server-side issues, but the symptom is that no clients get addresses, and the server is reachable.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that DHCP snooping drops are always visible in the switch's drop counters, but the trap here is that the drops occur at the DHCP server, not the switch, so candidates may incorrectly focus on switch-side issues like VLAN mismatches or MAC verification.

Detailed technical explanation

How to think about this question

DHCP snooping inserts option 82 by default on untrusted ports to provide relay agent information, such as the switch's bridge MAC and the ingress port. The DHCP server must be configured to trust this option (e.g., using 'ip dhcp relay information trust-all' on Cisco IOS) or strip it before processing; otherwise, the server treats the packet as invalid and drops it. In real-world scenarios, this often occurs when a legitimate DHCP server is moved behind a switch with DHCP snooping enabled, and the server's OS or DHCP service does not natively support option 82.

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.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

DHCP (IPv4 and IPv6) — This question tests DHCP (IPv4 and IPv6) — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The DHCP server is not configured to trust the relay agent information option (option 82), causing it to discard the requests. — When DHCP snooping is enabled, the switch inserts the relay agent information option (option 82) into DHCP requests received on untrusted ports. If the DHCP server is not configured to trust or process option 82, it will discard these requests, preventing clients from obtaining IP addresses even though the switch reports no drops. This is the most likely cause because the DHCP server is reachable and the switch shows no drops, indicating the issue lies with how the server handles the relayed packets.

What should I do if I get this 300-410 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.

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