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Network Infrastructure and Connectivity →hardTroubleshootingObjective-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
Gi0/110.0.0.1/302 km fiberR1Remote Switch

You are connected to R1 via console. R1's GigabitEthernet0/1 interface connects to a remote site switch over a 2 km fiber link. The current configuration shows speed and duplex set to 1000 Mbps and full, but the interface is down/down due to an SFP mismatch. Review the exhibit, identify the problem, and correct it so that the interface comes up and communicates at the correct speed and duplex. Additionally, ensure the interface is configured to auto-negotiate properly for future cable replacements.

Question 1hardTroubleshooting
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Exhibit

R1# show interfaces gigabitEthernet 0/1
GigabitEthernet0/1 is down, line protocol is down
  Hardware is GigabitEthernet, address is aabb.cc00.0101 (bia aabb.cc00.0101)
  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)
  Auto-duplex, Auto-speed, media type is SFP
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output never, 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 0/1 transceiver
Diagnostic Monitoring: Not supported

R1# show running-config interface gigabitEthernet 0/1
Building configuration...

Current configuration : 79 bytes
!
interface GigabitEthernet0/1
 no ip address
 shutdown
 speed 1000
 duplex full
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

✓

Replace the SFP with a 1000BASE-LX module, remove the manual speed and duplex settings, and issue the no shutdown command.

The interface was administratively shut down (shutdown command) and had hard-coded speed 1000 and duplex full, which is incompatible with the 2 km fiber link requiring a long-haul SFP (e.g., 1000BASE-LX). The correct fix is to remove the manual speed/duplex settings, enable auto-negotiation (which is default but overridden), and then no shutdown. For a 2 km link, a 1000BASE-LX SFP is required; the existing SFP (likely 1000BASE-SX, max 550 m) caused the link to be down. After replacing with the correct SFP, the interface should come up. Commands: interface Gi0/1, no speed, no duplex, no shutdown.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✓

    Replace the SFP with a 1000BASE-LX module, remove the manual speed and duplex settings, and issue the no shutdown command.

    Why this is correct

    This is correct because the 2 km fiber link requires a long-haul SFP (1000BASE-LX supports up to 5 km), and manual speed/duplex settings prevent proper auto-negotiation. Removing them restores default auto-negotiation, and no shutdown brings the interface up.

    Related concept

    Static NAT maps one inside address to one outside address.

  • ✗

    Replace the SFP with a 1000BASE-SX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.

    Why it's wrong here

    This is incorrect because 1000BASE-SX has a maximum distance of 550 m over multimode fiber, insufficient for a 2 km link. Additionally, manual speed/duplex settings are not recommended for fiber interfaces and can cause issues.

  • ✗

    Keep the existing SFP, change the speed to 100 and duplex to half, and issue the no shutdown command.

    Why it's wrong here

    This is incorrect because the interface is Gigabit Ethernet and does not support 100 Mbps speed; Gigabit Ethernet only operates at 1000 Mbps. Also, half duplex is not used with fiber links.

  • ✗

    Replace the SFP with a 1000BASE-LX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.

    Why it's wrong here

    This is incorrect because although the SFP replacement is correct, keeping manual speed and duplex settings prevents auto-negotiation, which is required for proper operation with future cable replacements. Cisco recommends using auto-negotiation on Gigabit Ethernet fiber interfaces.

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.

✓Replace the SFP with a 1000BASE-LX module, remove the manual speed and duplex settings, and issue the no shutdown command.Correct answer▾

Why this is correct

This is correct because the 2 km fiber link requires a long-haul SFP (1000BASE-LX supports up to 5 km), and manual speed/duplex settings prevent proper auto-negotiation. Removing them restores default auto-negotiation, and no shutdown brings the interface up.

✗Replace the SFP with a 1000BASE-SX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that 1000BASE-SX cannot support 2 km distances; it is limited to 550 m.

Why candidates choose this

Candidates might think any Gigabit SFP works for any distance, or that manual settings are always acceptable.

✗Keep the existing SFP, change the speed to 100 and duplex to half, and issue the no shutdown command.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that Gigabit Ethernet interfaces cannot be set to 100 Mbps; they only support 1000 Mbps or auto-negotiation.

Why candidates choose this

Candidates might confuse speed settings from FastEthernet or think reducing speed can compensate for distance issues.

✗Replace the SFP with a 1000BASE-LX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that manual speed/duplex settings should be removed to allow auto-negotiation; they are not recommended for fiber interfaces.

Why candidates choose this

Candidates might think manual settings are fine since they match the expected speed, but they overlook the auto-negotiation requirement.

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: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

  • Static NAT maps one inside address to one outside address.
  • PAT allows many inside hosts to share one public address using ports.
  • Inside local and inside global describe the private and translated addresses.
  • NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

  • Identify inside and outside interfaces first.
  • Check whether the scenario needs static NAT, dynamic NAT or PAT.
  • Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.

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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 — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: Replace the SFP with a 1000BASE-LX module, remove the manual speed and duplex settings, and issue the no shutdown command. — The interface was administratively shut down (shutdown command) and had hard-coded speed 1000 and duplex full, which is incompatible with the 2 km fiber link requiring a long-haul SFP (e.g., 1000BASE-LX). The correct fix is to remove the manual speed/duplex settings, enable auto-negotiation (which is default but overridden), and then no shutdown. For a 2 km link, a 1000BASE-LX SFP is required; the existing SFP (likely 1000BASE-SX, max 550 m) caused the link to be down. After replacing with the correct SFP, the interface should come up. Commands: interface Gi0/1, no speed, no duplex, no shutdown.

What should I do if I get this 200-301 question wrong?

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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Last reviewed: Jun 6, 2026

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