Question 753 of 1,819
Network Infrastructure and ConnectivityhardTroubleshootingObjective-mapped

CCNA Network Infrastructure and Connectivity Practice Question

This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
Gi0/010.1.1.1/30Gi0/010.1.1.2/30Cat6 cableR1R2

You are connected to R1. The link between R1's GigabitEthernet0/0 and R2's GigabitEthernet0/0 should operate at 1 Gbps full duplex, but the interface is showing errors and only negotiating at 100 Mbps half duplex. Diagnose and fix the fault, then verify the link is stable at the correct speed and duplex.

Question 1hardTroubleshooting
Full question →

Exhibit

R1# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
  Hardware is ISR4331-2x1GE, address is aabb.cc00.0100 (bia aabb.cc00.0100)
  Internet address is 10.1.1.1/30
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, 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: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     12345 packets input, 1234567 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     3456 input errors, 3456 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     12345 packets output, 1234567 bytes, 0 underruns
     0 output errors, 0 collisions, 0 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
R1# show interfaces gigabitEthernet 0/0 status
Port      Name               Status       Vlan    Duplex  Speed  Type
Gi0/0                        connected    1       Full   100    10/100/1000BaseTX

R1# show running-config interface gigabitEthernet 0/0
Building configuration...

Current configuration : 90 bytes
!
interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252
 duplex half
 speed 100
end

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

Remove the manual speed and duplex settings on R1's GigabitEthernet0/0 with 'no speed' and 'no duplex' to allow auto-negotiation.

The interface was manually configured with 'duplex half' and 'speed 100', which forced the link to 100 Mbps half duplex, causing CRC errors due to duplex mismatch. The correct fix is to remove these manual settings and allow auto-negotiation, or explicitly set both sides to 'speed 1000' and 'duplex full'. Since the remote side (R2) is set to auto (default), the simplest correction is to use 'no duplex' and 'no speed' on R1 to re-enable auto-negotiation. After the commands are applied, the interface should show 'Full-duplex, 1000Mb/s' and CRC errors should stop incrementing.

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.

  • Remove the manual speed and duplex settings on R1's GigabitEthernet0/0 with 'no speed' and 'no duplex' to allow auto-negotiation.

    Why this is correct

    This is correct because the interface was manually set to 100 Mbps half duplex, causing a duplex mismatch with R2's auto-negotiating interface. Removing these settings restores auto-negotiation, which will match R2's settings and establish 1 Gbps full duplex, eliminating CRC errors.

    Related concept

    Read the scenario before looking for a memorised answer.

  • Change the duplex setting to 'full' and speed to '1000' on R1's GigabitEthernet0/0.

    Why it's wrong here

    This is incorrect because while setting speed 1000 and duplex full would work if R2 were also manually configured, the question states R2 is set to auto. Manually setting speed and duplex on one side while the other side auto-negotiates can still cause a mismatch if the auto side does not match the manual settings correctly. The safer approach is to remove manual settings.

  • Replace the cable between R1 and R2 with a crossover cable.

    Why it's wrong here

    This is incorrect because modern Gigabit Ethernet interfaces support Auto-MDIX, which automatically detects and corrects cable type. The issue is not cable type but a speed/duplex mismatch caused by manual configuration.

  • Configure R2's GigabitEthernet0/0 with 'speed 100' and 'duplex half' to match R1's settings.

    Why it's wrong here

    This is incorrect because matching the wrong settings would stabilize the link at 100 Mbps half duplex, but the requirement is for 1 Gbps full duplex. This would not resolve the speed/duplex mismatch but would instead lock both sides into suboptimal settings.

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.

Remove the manual speed and duplex settings on R1's GigabitEthernet0/0 with 'no speed' and 'no duplex' to allow auto-negotiation.Correct answer

Why this is correct

This is correct because the interface was manually set to 100 Mbps half duplex, causing a duplex mismatch with R2's auto-negotiating interface. Removing these settings restores auto-negotiation, which will match R2's settings and establish 1 Gbps full duplex, eliminating CRC errors.

Change the duplex setting to 'full' and speed to '1000' on R1's GigabitEthernet0/0.Wrong answer — click to see why

Why this is wrong here

The specific factual error is that manually setting speed and duplex on one side while the other side is set to auto can lead to a mismatch; auto-negotiation is required for proper link establishment.

Why candidates choose this

Candidates pick this because they know that 1 Gbps full duplex is the desired setting and think explicitly configuring it will fix the issue, but they overlook the importance of consistent configuration on both ends.

Replace the cable between R1 and R2 with a crossover cable.Wrong answer — click to see why

Why this is wrong here

The specific factual error is that Auto-MDIX eliminates the need for crossover cables on modern interfaces; cable type is not the cause of the problem.

Why candidates choose this

Candidates pick this because they recall that duplex mismatches can sometimes be caused by incorrect cable types, but in this scenario the cable is not the issue.

Configure R2's GigabitEthernet0/0 with 'speed 100' and 'duplex half' to match R1's settings.Wrong answer — click to see why

Why this is wrong here

The specific factual error is that matching the incorrect settings does not achieve the desired speed and duplex; it only prevents errors at a lower performance level.

Why candidates choose this

Candidates pick this because they think consistency between both ends is the only requirement, ignoring the performance goal of 1 Gbps full duplex.

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.

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.

What to study next

Got this wrong? Here's your next step.

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.

Related practice questions

Related 200-301 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

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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: Remove the manual speed and duplex settings on R1's GigabitEthernet0/0 with 'no speed' and 'no duplex' to allow auto-negotiation. — The interface was manually configured with 'duplex half' and 'speed 100', which forced the link to 100 Mbps half duplex, causing CRC errors due to duplex mismatch. The correct fix is to remove these manual settings and allow auto-negotiation, or explicitly set both sides to 'speed 1000' and 'duplex full'. Since the remote side (R2) is set to auto (default), the simplest correction is to use 'no duplex' and 'no speed' on R1 to re-enable auto-negotiation. After the commands are applied, the interface should show 'Full-duplex, 1000Mb/s' and CRC errors should stop incrementing.

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.

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Last reviewed: Jun 6, 2026

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