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Question 308 of 1,052
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CCNA Practice Question: A network administrator is troubleshooting a…
This 200-301 practice question tests your understanding of 200-301 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.
Exhibit
R1# show running-config | section interface GigabitEthernet0/0 interface GigabitEthernet0/0 description Connection to Main Office ip address 192.168.1.1 255.255.255.0 no shutdown ! interface GigabitEthernet0/1 description Branch LAN VLAN 10 ip address 10.10.10.1 255.255.255.0 ip helper-address 10.1.1.10 no shutdown
A network administrator is troubleshooting a branch office where clients on VLAN 10 are failing to obtain IP addresses via DHCP. The DHCP server is located at the main office (10.1.1.10). The branch router (R1) has the following configuration. What is the most likely cause of the issue?
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 router does not have a route back to the client subnet for the DHCP server's reply.
The ip helper-address command is correctly configured on the interface facing the DHCP clients (GigabitEthernet0/1). However, the DHCP server (10.1.1.10) is on a different subnet (main office). The router needs a route back to the client subnet (10.10.10.0/24) to forward the DHCP offer. Without a route to 10.10.10.0/24, the DHCP server cannot reply. The missing route is the most likely cause. Options A, C, and D are incorrect because the ip helper-address is present, DHCP snooping is not shown to be enabled, and the interface is up.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 ip helper-address is missing from the interface facing the DHCP clients.
Why it's wrong here
The exhibit shows ip helper-address 10.1.1.10 on GigabitEthernet0/1, which is the correct interface for clients.
- ✓
The router does not have a route back to the client subnet for the DHCP server's reply.
Why this is correct
The DHCP relay agent forwards the request to the server, but the server must have a route back to the client subnet to send the offer. Without this route, the reply is dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
DHCP snooping is enabled and is blocking the DHCP packets.
Why it's wrong here
The exhibit does not show any DHCP snooping configuration; it is not mentioned in the running-config.
- ✗
The interface GigabitEthernet0/1 is in err-disabled state.
Why it's wrong here
The interface is configured with 'no shutdown' and no error condition is shown in the exhibit.
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 router does not have a route back to the client subnet for the DHCP server's reply.Correct answer▾
Why this is correct
The DHCP relay agent forwards the request to the server, but the server must have a route back to the client subnet to send the offer. Without this route, the reply is dropped.
✗The ip helper-address is missing from the interface facing the DHCP clients.Wrong answer — click to see why▾
Why this is wrong here
The ip helper-address is already configured on the correct interface.
✗DHCP snooping is enabled and is blocking the DHCP packets.Wrong answer — click to see why▾
Why this is wrong here
There is no evidence of DHCP snooping being enabled.
✗The interface GigabitEthernet0/1 is in err-disabled state.Wrong answer — click to see why▾
Why this is wrong here
The interface is administratively up and no err-disabled indication is present.
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: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
The exhibit shows ip helper-address 10.1.1.10 on GigabitEthernet0/1, which is the correct interface for clients.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: The router does not have a route back to the client subnet for the DHCP server's reply. — The ip helper-address command is correctly configured on the interface facing the DHCP clients (GigabitEthernet0/1). However, the DHCP server (10.1.1.10) is on a different subnet (main office). The router needs a route back to the client subnet (10.10.10.0/24) to forward the DHCP offer. Without a route to 10.10.10.0/24, the DHCP server cannot reply. The missing route is the most likely cause. Options A, C, and D are incorrect because the ip helper-address is present, DHCP snooping is not shown to be enabled, and the interface is up.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
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