CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. 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.
Network Topology
You are troubleshooting a PC (PC-A) connected to switch SW1, which is connected to router R1. PC-A has an APIPA address (169.254.23.45) and cannot reach the internet (203.0.113.1). You confirm that R1 has a correctly configured DHCP pool for the 192.168.10.0/24 subnet, but the DHCP service is not enabled. The network uses VLAN 10 with subnet 192.168.10.0/24. Verify and correct the configuration on PC-A, SW1, and R1 to restore full connectivity.
PC-A ipconfig output:
Ethernet adapter Ethernet0:
Connection-specific DNS Suffix . : example.local
IPv4 Address. . . . . . . . . . . : 169.254.23.45
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . :
SW1# show interfaces vlan 10
Vlan10 is up, line protocol is up
Internet address is 192.168.10.2/24
R1# show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0/0 192.168.10.1 YES manual up up
GigabitEthernet0/0/1 203.0.113.2 YES manual up up
R1# show running-config | section interface GigabitEthernet0/0/0
interface GigabitEthernet0/0/0
ip address 192.168.10.1 255.255.255.0
duplex auto
speed auto
R1# show running-config | include dhcp
ip dhcp excluded-address 192.168.10.1 192.168.10.10
ip dhcp pool VLAN10_POOL
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
dns-server 8.8.8.8
SW1# show running-config | include dhcp
! No DHCP configuration on SW1
PC-A ping 192.168.10.1
Pinging 192.168.10.1 with 32 bytes of data:
Reply from 169.254.23.45: Destination host unreachable.
PC-A ping 192.168.10.2
Pinging 192.168.10.2 with 32 bytes of data:
Reply from 169.254.23.45: Destination host unreachable.
A
Enable the DHCP service on R1 with the 'service dhcp' command.
The DHCP service is disabled by default on Cisco routers. Even if the DHCP pool is configured, the router will not respond to DHCP requests until 'service dhcp' is enabled. This command activates the DHCP server process, allowing R1 to assign IP addresses from the configured pool.
B
Configure a default gateway on PC-A with the IP address 192.168.10.1.
Why wrong: This is incorrect because PC-A has an APIPA address (169.254.23.45), which indicates it did not receive a DHCP lease. Manually setting a default gateway does not resolve the underlying issue of DHCP failure. The PC must first obtain a valid IP address via DHCP before a default gateway can be used.
C
Change the VLAN on SW1's interface connected to PC-A from VLAN 10 to VLAN 1.
Why wrong: This is incorrect because PC-A is configured for VLAN 10, and the DHCP pool is on subnet 192.168.10.0/24, which is associated with VLAN 10. Changing to VLAN 1 would place PC-A in a different subnet, preventing it from receiving a DHCP lease from R1's pool. The VLAN configuration is correct as is.
D
Add the 'ip helper-address' command on R1's interface connected to SW1.
Why wrong: This is incorrect because the DHCP server is on R1 itself, not on a remote server. The 'ip helper-address' command is used to forward DHCP broadcasts to a DHCP server on a different subnet. Since R1 is the DHCP server, no helper address is needed; the router will respond to DHCP requests on its directly connected interface.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable the DHCP service on R1 with the 'service dhcp' command.
The APIPA address (169.254.x.x) indicates that PC-A failed to obtain a DHCP lease. The correct solution is to enable the DHCP service on R1 with 'service dhcp', which is not running despite the configured pool. Option B is incorrect because setting a default gateway on PC-A with a static IP would still require a valid address in the subnet; the APIPA address cannot communicate with 192.168.10.1. Option C is wrong because the PC-A interface on SW1 is correctly assigned to VLAN 10. Option D is unnecessary since R1 is directly connected to the same subnet, so 'ip helper-address' is only used to forward DHCP broadcasts across router boundaries.
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.
✓
Enable the DHCP service on R1 with the 'service dhcp' command.
Why this is correct
The DHCP service is disabled by default on Cisco routers. Even if the DHCP pool is configured, the router will not respond to DHCP requests until 'service dhcp' is enabled. This command activates the DHCP server process, allowing R1 to assign IP addresses from the configured pool.
Related concept
Access ports place end devices into a single VLAN.
✗
Configure a default gateway on PC-A with the IP address 192.168.10.1.
Why it's wrong here
This is incorrect because PC-A has an APIPA address (169.254.23.45), which indicates it did not receive a DHCP lease. Manually setting a default gateway does not resolve the underlying issue of DHCP failure. The PC must first obtain a valid IP address via DHCP before a default gateway can be used.
✗
Change the VLAN on SW1's interface connected to PC-A from VLAN 10 to VLAN 1.
Why it's wrong here
This is incorrect because PC-A is configured for VLAN 10, and the DHCP pool is on subnet 192.168.10.0/24, which is associated with VLAN 10. Changing to VLAN 1 would place PC-A in a different subnet, preventing it from receiving a DHCP lease from R1's pool. The VLAN configuration is correct as is.
✗
Add the 'ip helper-address' command on R1's interface connected to SW1.
Why it's wrong here
This is incorrect because the DHCP server is on R1 itself, not on a remote server. The 'ip helper-address' command is used to forward DHCP broadcasts to a DHCP server on a different subnet. Since R1 is the DHCP server, no helper address is needed; the router will respond to DHCP requests on its directly connected interface.
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.
✓Enable the DHCP service on R1 with the 'service dhcp' command.Correct answer▾
Why this is correct
The DHCP service is disabled by default on Cisco routers. Even if the DHCP pool is configured, the router will not respond to DHCP requests until 'service dhcp' is enabled. This command activates the DHCP server process, allowing R1 to assign IP addresses from the configured pool.
✗Configure a default gateway on PC-A with the IP address 192.168.10.1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the PC's APIPA address shows DHCP failure; setting a default gateway does not fix the lack of IP address assignment.
Why candidates choose this
Candidates might think that a missing default gateway is the primary issue, especially if they see that the PC has an IP address (even an APIPA) and assume the gateway is the only missing piece.
✗Change the VLAN on SW1's interface connected to PC-A from VLAN 10 to VLAN 1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that VLAN 1 is the default VLAN but does not match the subnet used by the DHCP pool; changing VLANs would break connectivity.
Why candidates choose this
Candidates might think that using the default VLAN (VLAN 1) is always correct, or they might confuse VLAN assignment with IP subnetting.
✗Add the 'ip helper-address' command on R1's interface connected to SW1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 'ip helper-address' is for relaying DHCP requests to a remote server, not for enabling a local DHCP server.
Why candidates choose this
Candidates often associate DHCP troubleshooting with the 'ip helper-address' command and may apply it unnecessarily when the DHCP server is local.
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
This is incorrect because the DHCP server is on R1 itself, not on a remote server. The 'ip helper-address' command is used to forward DHCP broadcasts to a DHCP server on a different subnet. Since R1 is the DHCP server, no helper address is needed; the router will respond to DHCP requests on its directly connected interface.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
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.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: Enable the DHCP service on R1 with the 'service dhcp' command. — The APIPA address (169.254.x.x) indicates that PC-A failed to obtain a DHCP lease. The correct solution is to enable the DHCP service on R1 with 'service dhcp', which is not running despite the configured pool. Option B is incorrect because setting a default gateway on PC-A with a static IP would still require a valid address in the subnet; the APIPA address cannot communicate with 192.168.10.1. Option C is wrong because the PC-A interface on SW1 is correctly assigned to VLAN 10. Option D is unnecessary since R1 is directly connected to the same subnet, so 'ip helper-address' is only used to forward DHCP broadcasts across router boundaries.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.