The answer is to configure R1’s interface with the `duplex half` command to resolve the full half duplex mismatch fix. This is correct because the `show interfaces` output reveals a classic duplex mismatch: R1 is set to full duplex while R2 is locked to half duplex, both at 100 Mb/s. On the full-duplex side, simultaneous transmissions cause corrupted frames, shown by high CRC errors on R1; on the half-duplex side, collisions are normal due to CSMA/CD, but no CRC errors appear because collisions trigger retransmissions. On the CCNA 200-301 v2 exam, this scenario tests your ability to interpret interface error counters and apply the correct `duplex half` command from the accessible router—since R2 is fixed, you must match its half-duplex setting rather than forcing full duplex. A common trap is assuming you should set both to full duplex, but the exam expects you to fix the mismatch from the side you control. Memory tip: “CRC on full, collisions on half—match the half to stop the laugh.”
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 connected to R1. The link between R1 and R2 is experiencing packet loss and slow performance. Examine the following partial show interface output:
R1# show interfaces g0/0
GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is aabb.cc00.0100 (bia aabb.cc00.0100)
Internet address is 10.0.0.1/30
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, link type is auto, media type is RJ45
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 12000 bits/sec, 10 packets/sec
5 minute output rate 15000 bits/sec, 12 packets/sec
12345 packets input, 987654 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
12345 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
67890 packets output, 543210 bytes, 0 underruns
0 output errors, 0 collisions, 12 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
A
Configure the interface with 'duplex half' to match the half-duplex setting on R2.
This is correct because the symptoms (high input errors without CRC errors on R1) indicate a duplex mismatch, with R1 set to full and R2 likely set to half. Setting R1 to half-duplex matches the duplex setting on R2, eliminating collisions and packet loss.
B
Configure the interface with 'speed 100' to force the link speed to 100 Mbps.
Why wrong: This is incorrect because the issue is duplex mismatch, not speed mismatch. Forcing speed alone does not resolve collisions caused by duplex mismatch; both speed and duplex must match.
C
Replace the Ethernet cable with a new one to fix the physical layer issue.
Why wrong: This is incorrect because a faulty cable typically causes CRC errors, runts, or giants, not the high input error count without CRC errors seen here. The error pattern is classic for duplex mismatch.
D
Configure the interface with 'no shutdown' to bring the interface up.
Why wrong: This is incorrect because the interface is already up (as shown in the output). The issue is performance-related, not administrative down.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the interface with 'duplex half' to match the half-duplex setting on R2.
The output reveals a duplex mismatch. R1 is operating in full‑duplex mode, while R2 is in half‑duplex mode. On the full‑duplex side (R1), simultaneous transmissions from both ends result in corrupted frames, visible as a high count of CRC errors. On the half‑duplex side (R2), ordinary collisions occur because R2 uses CSMA/CD, but no CRC errors are seen because it detects collisions and retransmits. The only immediate fix from R1—since R2 is fixed at half‑duplex—is to change R1's interface to half‑duplex using the command 'duplex half', which matches the settings and stops the corrupted frames. (Long‑term, both sides should ideally be set to full‑duplex, but that requires access to R2.)
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.
✓
Configure the interface with 'duplex half' to match the half-duplex setting on R2.
Why this is correct
This is correct because the symptoms (high input errors without CRC errors on R1) indicate a duplex mismatch, with R1 set to full and R2 likely set to half. Setting R1 to half-duplex matches the duplex setting on R2, eliminating collisions and packet loss.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure the interface with 'speed 100' to force the link speed to 100 Mbps.
Why it's wrong here
This is incorrect because the issue is duplex mismatch, not speed mismatch. Forcing speed alone does not resolve collisions caused by duplex mismatch; both speed and duplex must match.
✗
Replace the Ethernet cable with a new one to fix the physical layer issue.
Why it's wrong here
This is incorrect because a faulty cable typically causes CRC errors, runts, or giants, not the high input error count without CRC errors seen here. The error pattern is classic for duplex mismatch.
✗
Configure the interface with 'no shutdown' to bring the interface up.
Why it's wrong here
This is incorrect because the interface is already up (as shown in the output). The issue is performance-related, not administrative down.
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.
✓Configure the interface with 'duplex half' to match the half-duplex setting on R2.Correct answer▾
Why this is correct
This is correct because the symptoms (high input errors without CRC errors on R1) indicate a duplex mismatch, with R1 set to full and R2 likely set to half. Setting R1 to half-duplex matches the duplex setting on R2, eliminating collisions and packet loss.
✗Configure the interface with 'speed 100' to force the link speed to 100 Mbps.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that speed mismatch does not cause the high input error count without CRC errors; duplex mismatch does.
Why candidates choose this
Candidates might think that packet loss is due to speed mismatch, especially if they see 'speed' in the output, but the error pattern points to duplex.
✗Replace the Ethernet cable with a new one to fix the physical layer issue.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that cable issues produce CRC errors, not just input errors; the absence of CRC errors rules out cable problems.
Why candidates choose this
Candidates often jump to cable replacement when they see errors, but the specific error type (input errors without CRC) points to duplex mismatch.
✗Configure the interface with 'no shutdown' to bring the interface up.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 'no shutdown' is used to enable an interface that is administratively down; here the interface is up and passing traffic.
Why candidates choose this
Candidates might think the interface is down due to errors, but the output shows it is up; they may confuse error counters with interface state.
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
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
This is incorrect because the interface is already up (as shown in the output). The issue is performance-related, not administrative down.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: Configure the interface with 'duplex half' to match the half-duplex setting on R2. — The output reveals a duplex mismatch. R1 is operating in full‑duplex mode, while R2 is in half‑duplex mode. On the full‑duplex side (R1), simultaneous transmissions from both ends result in corrupted frames, visible as a high count of CRC errors. On the half‑duplex side (R2), ordinary collisions occur because R2 uses CSMA/CD, but no CRC errors are seen because it detects collisions and retransmits. The only immediate fix from R1—since R2 is fixed at half‑duplex—is to change R1's interface to half‑duplex using the command 'duplex half', which matches the settings and stops the corrupted frames. (Long‑term, both sides should ideally be set to full‑duplex, but that requires access to R2.)
What should I do if I get this 200-301 question wrong?
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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.