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Question 1,253 of 1,052
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CCNA Practice Question: A network administrator is troubleshooting a new…
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.
A network administrator is troubleshooting a new branch office where hosts in VLAN 20 on switch SW1 cannot obtain IP addresses from the DHCP server located at 192.168.10.5 in the main data center. The router R1 is configured as the default gateway for VLAN 20 with interface GigabitEthernet0/1.20. The administrator verifies that the DHCP server is reachable and has available addresses. What configuration change should the administrator make to resolve the issue?
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
✓
Configure the 'ip helper-address 192.168.10.5' command on the router interface GigabitEthernet0/1.20.
The correct answer is B: configure the 'ip helper-address 192.168.10.5' command on the router interface facing the client hosts. DHCP is a broadcast-based protocol, and broadcasts are typically not forwarded across subnets. The ip helper-address feature converts the DHCP broadcast from clients into a unicast directed to the DHCP server, allowing hosts in different subnets to obtain IP addresses. Option A (configuring a static IP on the server) does not solve the client-side issue. Option C (enabling DHCP snooping without proper configuration) might block DHCP messages. Option D (increasing the DHCP lease time) does not address the connectivity problem.
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.
- ✗
Configure a static IP address on the DHCP server to ensure it is always reachable.
- ✓
Configure the 'ip helper-address 192.168.10.5' command on the router interface GigabitEthernet0/1.20.
- ✗
Enable DHCP snooping globally on the switch SW1.
Why it's wrong here
DHCP snooping is a security feature that filters untrusted DHCP messages; it does not relay DHCP broadcasts across subnets.
- ✗
Increase the DHCP lease time on the server to 30 days.
Why it's wrong here
The lease time affects how long clients keep their IP addresses, but it does not enable DHCP broadcasts to cross subnets.
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.
✓Configure the 'ip helper-address 192.168.10.5' command on the router interface GigabitEthernet0/1.20.Correct answer▾
Why this is correct
The ip helper-address command enables the router to forward DHCP broadcasts as unicasts to the specified DHCP server, allowing clients in VLAN 20 to obtain IP addresses from the remote server.
✗Configure a static IP address on the DHCP server to ensure it is always reachable.Wrong answer — click to see why▾
Why this is wrong here
A static IP on the server does not forward broadcasts across subnets; the server's reachability is not the issue.
✗Enable DHCP snooping globally on the switch SW1.Wrong answer — click to see why▾
Why this is wrong here
Enabling DHCP snooping without proper configuration could block legitimate DHCP traffic, and it does not solve the broadcast forwarding issue.
✗Increase the DHCP lease time on the server to 30 days.Wrong answer — click to see why▾
Why this is wrong here
The problem is not about lease duration; clients cannot receive any DHCP offers because broadcasts are not forwarded.
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.
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: Configure the 'ip helper-address 192.168.10.5' command on the router interface GigabitEthernet0/1.20. — The correct answer is B: configure the 'ip helper-address 192.168.10.5' command on the router interface facing the client hosts. DHCP is a broadcast-based protocol, and broadcasts are typically not forwarded across subnets. The ip helper-address feature converts the DHCP broadcast from clients into a unicast directed to the DHCP server, allowing hosts in different subnets to obtain IP addresses. Option A (configuring a static IP on the server) does not solve the client-side issue. Option C (enabling DHCP snooping without proper configuration) might block DHCP messages. Option D (increasing the DHCP lease time) does not address the connectivity problem.
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.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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