Question 825 of 1,389
CCNA Switching and Network Access Practice Question
A network engineer is troubleshooting a connectivity issue between two hosts on different VLANs. The engineer captures traffic on an IOS-XE router's GigabitEthernet0/1 interface using embedded packet capture (EPC). The output shows ARP requests from Host A (192.168.1.10) but no ARP replies from Host B (192.168.2.20). What is the most likely cause of this issue?
⚠ Common exam trap
Cisco often tests the misconception that a router automatically routes between VLANs if it is connected to a switch via a trunk, but the router must have an IP address in each VLAN's subnet to respond to ARP and forward traffic.
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's interface does not have an IP address configured in the VLAN 2 subnet.
The router's GigabitEthernet0/1 interface must have an IP address in the same subnet as Host B (192.168.2.20) to act as the default gateway for VLAN 2. Without an IP address in the VLAN 2 subnet, the router cannot respond to ARP requests for that subnet, so Host A's ARP requests for Host B go unanswered. This is the most likely cause because the router performs inter-VLAN routing only when it has an interface (or subinterface) with an IP address in the destination VLAN's subnet.
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 router's interface is configured as an access port instead of a trunk.
Why it's wrong here
A trunk is used to carry multiple VLANs, but if the router is directly connected to each host or to a switch with separate access ports, a trunk may not be required. The issue is more likely the lack of an IP address on the router's interface for VLAN 2.
- ✓
The router's interface does not have an IP address configured in the VLAN 2 subnet.
Why this is correct
For inter-VLAN routing, the router must have an IP address in each VLAN's subnet to act as the default gateway and respond to ARP requests. Without an IP in VLAN 2, it cannot reply to ARP requests for 192.168.2.20.
- ✗
Host A is in a different VLAN than the router's interface.
Why it's wrong here
ARP requests are broadcast at Layer 2. If the router's interface is in the same VLAN as Host A, it will receive the ARP request. The issue is that the router does not reply, likely because it has no IP in the destination subnet.
- ✗
The router's interface has a duplex mismatch with the switch.
Why it's wrong here
A duplex mismatch would cause frame errors and retransmissions, but it would not specifically prevent ARP replies. The capture shows ARP requests but no replies, pointing to a Layer 3 addressing issue rather than a physical layer problem.
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's interface does not have an IP address configured in the VLAN 2 subnet.Correct answer▾
Why this is correct
For inter-VLAN routing, the router must have an IP address in each VLAN's subnet to act as the default gateway and respond to ARP requests. Without an IP in VLAN 2, it cannot reply to ARP requests for 192.168.2.20.
✗The router's interface is configured as an access port instead of a trunk.Wrong answer — click to see why▾
Why this is wrong here
The router's interface is a routed port, not a switchport; access/trunk concepts apply to switch interfaces. Even if it were a switch interface, the issue is about ARP replies, which require Layer 3 addressing, not trunking.
Why candidates choose this
Students often confuse router interfaces with switch interfaces and may think that VLAN tagging is required for inter-VLAN routing, but in this scenario the router is likely using router-on-a-stick or routed interfaces.
✗Host A is in a different VLAN than the router's interface.Wrong answer — click to see why▾
Why this is wrong here
ARP requests are Layer 2 broadcasts; if the router's interface is in the same VLAN as Host A, it will receive the request. The problem is that the router does not reply, indicating it lacks an IP in the destination subnet.
Why candidates choose this
Test-takers may think that VLAN mismatch prevents the router from seeing the ARP request, but the capture shows the request is received; the issue is at Layer 3.
✗The router's interface has a duplex mismatch with the switch.Wrong answer — click to see why▾
Why this is wrong here
Duplex mismatch causes CRC errors and collisions, but ARP requests would still be received and could be replied to. The capture shows clean ARP requests with no replies, pointing to a Layer 3 issue, not physical layer.
Why candidates choose this
Duplex mismatch is a common troubleshooting topic, and students may jump to physical layer issues without considering the specific symptom of missing ARP replies.
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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Last reviewed: Jun 11, 2026
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