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Network Infrastructure and Connectivity →hardTroubleshootingObjective-mapped

Quick Answer

The correct answer is to configure speed 100 and duplex full on G0/0, then no shutdown, and after the link is up, replace the 1000BASE-T SFP with a 1000BASE-LX SFP, then reconfigure the interface with speed auto and duplex auto. This is correct because manually setting speed and duplex on a copper link bypasses auto-negotiation failures, which often occur when one side fails to agree on parameters, leaving the interface in a down state. Once the copper link is stable, the SFP must be swapped to a 1000BASE-LX module for a 5 km fiber run, but the interface must be reconfigured to auto-negotiation because fiber SFPs rely on link pulses rather than forced settings—forcing 100 Mbps on a 1000BASE-LX SFP would prevent the link from coming up entirely. On the CCNA 200-301 v2 exam, this tests your understanding of interface configuration, SFP compatibility, and the critical difference between copper and fiber auto-negotiation. A common trap is assuming the interface automatically adapts to a new SFP, but you must explicitly change the speed and duplex settings. Memory tip: copper needs force, fiber needs auto—swap the SFP, then swap the config.

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
G0/010.0.0.1/30G0/010.0.0.2/301000BASE-LX SMF 5 kmR1R2

You are connected to R1 via the console. R1 and R2 are directly connected via their GigabitEthernet0/0 interfaces. Configure R1's G0/0 for 100 Mbps full-duplex operation. Then, diagnose and fix an auto-negotiation failure that prevents the link from coming up. Finally, replace the existing 1000BASE-T SFP with a 1000BASE-LX SFP to support a new 5 km fiber run. Ensure the link is up and working.

Question 1hardTroubleshooting
Full question →

Exhibit

R1#show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
  Internet address is 10.0.0.1/30
  MTU 1500 bytes, BW 1000 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, 1000Mb/s, media type is 10/100/1000BaseTX
  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
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     0 packets output, 0 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            notconnect   1      auto   auto 10/100/1000BaseTX

R1#show interfaces gigabitEthernet 0/0 | include duplex|speed
  Full-duplex, 1000Mb/s

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

Current configuration : 45 bytes
!
interface GigabitEthernet0/0
 no ip address
 shutdown
end

R1#show interfaces gigabitEthernet 0/0 | include media type
  media type is 10/100/1000BaseTX

R1#show interfaces gigabitEthernet 0/0 transceiver
Diagnostic Monitoring is not supported

R1#show interfaces gigabitEthernet 0/0 | include errors|CRC|collision
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 output errors, 0 collisions, 0 interface resets

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

✓

Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed auto and duplex auto. Finally, verify the link state.

First, set speed to 100 and duplex to full on GigabitEthernet0/0, then issue no shutdown to bring the link up. This manual configuration resolves potential auto-negotiation failures on the copper link. After confirming the link, issue shutdown on the interface before physically swapping the SFP to a 1000BASE-LX module. Then, configure the interface with speed auto and duplex auto (standard for fiber) and no shutdown. Finally, verify the link state. Option A is wrong because the interface does not automatically adjust to the new SFP's capabilities; explicit reconfiguration is required. Option B is wrong because forcing speed 1000 and duplex full is unnecessary and may cause negotiation issues. Option D is wrong because maintaining 100 Mbps on a 1000BASE-LX SFP would prevent the link from operating.

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 speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP; the interface will automatically detect the new SFP and adjust speed/duplex.

    Why it's wrong here

    This is incorrect because after replacing the SFP, the interface must be configured with the appropriate speed and duplex settings (typically auto for fiber) and verified; it does not automatically adjust without configuration.

  • ✗

    Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed 1000 and duplex full to match the new SFP.

    Why it's wrong here

    This is incorrect because 1000BASE-LX SFP operates at 1000 Mbps (1 Gbps) and typically uses auto-negotiation for duplex; forcing speed 1000 and duplex full may cause a mismatch if the remote side is set to auto.

  • ✓

    Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed auto and duplex auto. Finally, verify the link state.

    Why this is correct

    This is correct because after setting the initial speed/duplex to 100/full and bringing the link up, replacing the SFP with a 1000BASE-LX requires configuring the interface for auto-negotiation (speed auto, duplex auto) to ensure proper operation over fiber. Verifying the link state confirms the link is up.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed 100 and duplex full to maintain consistency.

    Why it's wrong here

    This is incorrect because the 1000BASE-LX SFP operates at 1000 Mbps, not 100 Mbps; configuring speed 100 would cause a speed mismatch and the link would not come up.

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 speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed auto and duplex auto. Finally, verify the link state.Correct answer▾

Why this is correct

This is correct because after setting the initial speed/duplex to 100/full and bringing the link up, replacing the SFP with a 1000BASE-LX requires configuring the interface for auto-negotiation (speed auto, duplex auto) to ensure proper operation over fiber. Verifying the link state confirms the link is up.

✗Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP; the interface will automatically detect the new SFP and adjust speed/duplex.Wrong answer — click to see why▾

Why this is wrong here

The interface does not automatically adjust speed/duplex when an SFP is replaced; you must configure the interface accordingly (e.g., speed auto, duplex auto) and ensure the link is up.

Why candidates choose this

Candidates may think that SFP modules are hot-swappable and the interface auto-negotiates without manual intervention, but in many cases, especially when changing from copper to fiber, configuration is required.

✗Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed 1000 and duplex full to match the new SFP.Wrong answer — click to see why▾

Why this is wrong here

Forcing speed and duplex on a fiber link can lead to auto-negotiation failure; the correct practice is to use auto-negotiation (speed auto, duplex auto) for fiber SFPs.

Why candidates choose this

Candidates may assume that since the SFP is 1000BASE, they should manually set speed to 1000 and duplex to full, but this can cause issues if the remote side is set to auto.

✗Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed 100 and duplex full to maintain consistency.Wrong answer — click to see why▾

Why this is wrong here

The SFP type determines the supported speed; 1000BASE-LX is gigabit Ethernet, so the interface must be configured for 1000 Mbps (or auto) to match.

Why candidates choose this

Candidates might think that since the initial configuration used speed 100, they should keep it the same, but the new SFP requires a different speed setting.

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.

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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: Configure speed 100 and duplex full on G0/0, then no shutdown. After the link is up, remove the 1000BASE-T SFP and insert the 1000BASE-LX SFP, then configure the interface with speed auto and duplex auto. Finally, verify the link state. — First, set speed to 100 and duplex to full on GigabitEthernet0/0, then issue no shutdown to bring the link up. This manual configuration resolves potential auto-negotiation failures on the copper link. After confirming the link, issue shutdown on the interface before physically swapping the SFP to a 1000BASE-LX module. Then, configure the interface with speed auto and duplex auto (standard for fiber) and no shutdown. Finally, verify the link state. Option A is wrong because the interface does not automatically adjust to the new SFP's capabilities; explicit reconfiguration is required. Option B is wrong because forcing speed 1000 and duplex full is unnecessary and may cause negotiation issues. Option D is wrong because maintaining 100 Mbps on a 1000BASE-LX SFP would prevent the link from operating.

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 →

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Same concept, more angles

1 more ways this is tested on 200-301

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. You are connected to R1. Configure the G0/0 interface to match the speed (100 Mbps) and duplex (full) of the connected switch port, then diagnose and fix an auto-negotiation failure that has caused excessive CRC errors. Finally, select and replace the SFP module on G0/0 with one that supports a 5 km fiber link, using the correct cable type.

hard
  • ✓ A.Set speed 100, duplex full; replace SFP with 1000BASE-LX; use single-mode fiber (SMF).
  • B.Set speed 100, duplex half; replace SFP with 1000BASE-SX; use multimode fiber (MMF).
  • C.Set speed 1000, duplex full; replace SFP with 1000BASE-LX; use single-mode fiber (SMF).
  • D.Set no speed, no duplex (auto); replace SFP with 1000BASE-LX; use single-mode fiber (SMF).

Why A: The interface is up but line protocol is down, indicating a layer 1 issue. The switch port is manually set to 100 Mbps/full duplex, but R1 is using auto-negotiation, causing a mismatch. First, set the speed to 100 and duplex to full on G0/0. The CRC errors may appear later if cabling is faulty; for a 5 km fiber link, you need a 1000BASE-LX SFP (single-mode) and single-mode fiber (SMF). Verify the SFP is recognized and the link comes up.

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Last reviewed: Jun 6, 2026

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