CCNA Network Infrastructure and Connectivity Practice Question
A host cannot communicate with its default gateway. The technician uses the show arp command on the host and sees that the ARP entry for the gateway IP is incomplete. The technician has already verified that the Ethernet cable is securely connected and the switch port is active. What should the technician do next?
⚠ Common exam trap
Cisco often tests the distinction between Layer 2 connectivity (ARP, VLANs) and Layer 3 connectivity (routing), leading candidates to incorrectly focus on routing tables or ARP cache clearing when the real issue is a VLAN mismatch.
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
✓
Check the switch port’s VLAN configuration and ensure the host and router interface are in the same VLAN.
An incomplete ARP entry for the default gateway indicates that the host sent an ARP request but never received a reply. Since the physical layer (cable and switch port) is verified as operational, the most likely cause is a Layer 2 mismatch: the host and the router interface are in different VLANs, preventing the ARP reply from reaching the host. Checking the switch port's VLAN configuration ensures both devices are in the same broadcast domain, which is required for ARP to function.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check the switch port’s VLAN configuration and ensure the host and router interface are in the same VLAN.
Why this is correct
If the host and gateway are in different VLANs, the ARP request broadcast never reaches the gateway, so the entry stays incomplete. This step directly addresses the most probable Layer 2 fault after excluding physical issues.
- ✗
Replace the Ethernet cable between the host and the switch.
Why it's wrong here
Replacing the cable is premature because the switch port is already active and the host is successfully transmitting frames at Layer 1. An ARP entry that remains incomplete indicates the host sent an ARP request but received no reply, which points to a Layer 2 or Layer 3 logical issue (such as a VLAN mismatch or misconfigured gateway interface), not a physical medium failure. Since link status and port operation have been verified, swapping the cable before checking VLAN configuration wastes time and does not address the actual cause.
- ✗
Clear the ARP cache on the host and attempt to ping the gateway again.
Why it's wrong here
Clearing the ARP cache only removes the stale entry and forces the host to send a new ARP request; it does not resolve the underlying reason the gateway is not responding. If the VLAN mismatch or gateway interface issue persists, the cache will repopulate with an incomplete entry after the next ARP timeout, and the ping will still fail. This action is a useful diagnostic step to confirm the situation, but it is not a corrective action for the root cause.
- ✗
Check the router’s routing table for a route to the host’s subnet.
Why it's wrong here
The default gateway IP is the router’s own interface address; it does not need a route to respond to an ARP request. ARP resolution is a Layer 2 process for a directly connected network, not a routing decision.
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.
✓Check the switch port’s VLAN configuration and ensure the host and router interface are in the same VLAN.Correct answer▾
Why this is correct
If the host and gateway are in different VLANs, the ARP request broadcast never reaches the gateway, so the entry stays incomplete. This step directly addresses the most probable Layer 2 fault after excluding physical issues.
✗Replace the Ethernet cable between the host and the switch.Wrong answer — click to see why▾
Why this is wrong here
Candidates may equate a physical link symptom with a faulty cable, but the port’s active status indicates a good L1 connection. This action skips necessary logical checks.
✗Clear the ARP cache on the host and attempt to ping the gateway again.Wrong answer — click to see why▾
Why this is wrong here
This is a common ‘quick fix’ mindset, but in a structured troubleshooting process, clearing the cache hides information without solving the root cause.
✗Check the router’s routing table for a route to the host’s subnet.Wrong answer — click to see why▾
Why this is wrong here
Candidates might confuse local ARP failure with reachability issues to a remote subnet, but the gateway is the router itself. Routing is irrelevant until the destination is off-segment.
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
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
Collision Domains and Broadcast Domains
Key term
Ethernet
Ethernet is a wired networking technology that connects devices like computers, printers, and servers to each other and to the internet using cables.
Key term
ARP request
An ARP request is a network broadcast message sent by a device to discover the hardware (MAC) address of another device on the same local network given its IP address.
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JA
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.