- A
The Ethernet cable is faulty, causing intermittent physical layer failures.
Why wrong: A faulty cable would typically result in the interface being down (down/down) or flapping (up/down). Since both interfaces show an up/up state, the physical layer is functioning correctly.
- B
A duplex mismatch exists between R1 and R2, causing one-way communication.
Why wrong: A duplex mismatch causes CRC errors, late collisions, and poor performance, but it does not entirely block all traffic. More importantly, even with matching duplex settings, the different subnets would still prevent any ping from succeeding.
- C
A routing protocol is not configured to allow the routers to learn about each other's directly connected networks.
Why wrong: Routers automatically place directly connected subnets into their routing table when the interface IP matches that subnet. Since these routers belong to two different subnets (192.168.1.0/24 and 192.168.2.0/24), they do not have routes to each other’s local network. However, a routing protocol would not help because they are on the same Ethernet segment and would still need to be in the same subnet for neighbor adjacency. The real cause is the IP mismatch, not routing protocol absence.
- D
The IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication.
When two devices are in the same broadcast domain and have IP addresses in different subnets, they do not consider each other as local destinations. Router R1 will not attempt to ARP for 192.168.2.1 because it believes that address is in a different network, making the ping fail even though link status is up/up.
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.
A technician is troubleshooting a connection between two routers, R1 and R2, connected back-to-back using Ethernet cables. Both routers have their interfaces configured and are in an 'up/up' state. R1's interface uses 192.168.1.1/24, and R2's interface uses 192.168.2.1/24. When the technician attempts to ping R2 from R1, the ping fails. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication.
The ping fails because R1's interface is configured with IP address 192.168.1.1/24, which places it in the 192.168.1.0/24 subnet, while R2's interface uses 192.168.2.1/24, placing it in the 192.168.2.0/24 subnet. For two devices to communicate directly at Layer 3 over a single Ethernet link, their IP addresses must belong to the same subnet. Since these addresses are in different subnets, R1 will see the destination as unreachable and will not even attempt to send an ARP request for R2's MAC address, resulting in a failed ping.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 Ethernet cable is faulty, causing intermittent physical layer failures.
Why it's wrong here
A faulty cable would typically result in the interface being down (down/down) or flapping (up/down). Since both interfaces show an up/up state, the physical layer is functioning correctly.
- ✗
A duplex mismatch exists between R1 and R2, causing one-way communication.
Why it's wrong here
A duplex mismatch causes CRC errors, late collisions, and poor performance, but it does not entirely block all traffic. More importantly, even with matching duplex settings, the different subnets would still prevent any ping from succeeding.
- ✗
A routing protocol is not configured to allow the routers to learn about each other's directly connected networks.
Why it's wrong here
Routers automatically place directly connected subnets into their routing table when the interface IP matches that subnet. Since these routers belong to two different subnets (192.168.1.0/24 and 192.168.2.0/24), they do not have routes to each other’s local network. However, a routing protocol would not help because they are on the same Ethernet segment and would still need to be in the same subnet for neighbor adjacency. The real cause is the IP mismatch, not routing protocol absence.
- ✓
The IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication.
Why this is correct
When two devices are in the same broadcast domain and have IP addresses in different subnets, they do not consider each other as local destinations. Router R1 will not attempt to ARP for 192.168.2.1 because it believes that address is in a different network, making the ping fail even though link status is up/up.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
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 IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication.Correct answer▾
Why this is correct
When two devices are in the same broadcast domain and have IP addresses in different subnets, they do not consider each other as local destinations. Router R1 will not attempt to ARP for 192.168.2.1 because it believes that address is in a different network, making the ping fail even though link status is up/up.
✗The Ethernet cable is faulty, causing intermittent physical layer failures.Wrong answer — click to see why▾
Why this is wrong here
Candidates might suspect a physical issue first, but the up/up status definitively rules out a cable or hardware problem.
✗A duplex mismatch exists between R1 and R2, causing one-way communication.Wrong answer — click to see why▾
Why this is wrong here
Candidates commonly associate ‘cannot ping’ with duplex mismatches, forgetting that the fundamental issue here is the IP subnet mismatch.
✗A routing protocol is not configured to allow the routers to learn about each other's directly connected networks.Wrong answer — click to see why▾
Why this is wrong here
The trap is thinking that a routing protocol is always needed for inter-subnet communication, overlooking that directly connected devices on the same broadcast domain must share a common subnet.
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: answer the scenario, not the keyword
Cisco often tests the concept that directly connected devices must share the same subnet, and the trap here is that candidates assume 'up/up' means Layer 3 connectivity is guaranteed, or they mistakenly think a routing protocol is needed to exchange routes between directly connected interfaces.
Trap categories for this question
Command / output trap
A faulty cable would typically result in the interface being down (down/down) or flapping (up/down). Since both interfaces show an up/up state, the physical layer is functioning correctly.
Detailed technical explanation
How to think about this question
When two hosts are connected directly via Ethernet, they must be on the same IP subnet to perform ARP and send frames to each other. If the source IP and destination IP are in different subnets, the source will check its routing table and, lacking a route to the destination network, will drop the packet or send it to a default gateway—neither of which exists here. This is governed by the host's IP forwarding logic and the subnet mask; the /24 mask means the first 24 bits of the IP address define the network, so 192.168.1.0/24 and 192.168.2.0/24 are distinct networks.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication. — The ping fails because R1's interface is configured with IP address 192.168.1.1/24, which places it in the 192.168.1.0/24 subnet, while R2's interface uses 192.168.2.1/24, placing it in the 192.168.2.0/24 subnet. For two devices to communicate directly at Layer 3 over a single Ethernet link, their IP addresses must belong to the same subnet. Since these addresses are in different subnets, R1 will see the destination as unreachable and will not even attempt to send an ARP request for R2's MAC address, resulting in a failed ping.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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.
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