CCNA Network Infrastructure and Connectivity Practice Question
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.
⚠ Common exam trap
Do not assume that configuring a DHCP pool is sufficient; the DHCP service must be explicitly enabled with 'service dhcp'. Also, remember that APIPA addresses indicate DHCP failure, not just a missing gateway.
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
✓
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.
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.
- ✗
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?”
Visual reference
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Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.