CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
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.
⚠ Common exam trap
Trap: Candidates may focus only on the SFP replacement and forget to remove manual speed/duplex settings, or they may choose an SFP with insufficient distance. Remember that Gigabit Ethernet fiber interfaces should use auto-negotiation, and manual settings are only for troubleshooting or specific legacy scenarios.
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.
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.
- ✗
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 configuration is invalid because the SFP slot is Gigabit Ethernet and the installed SFP is a 1000BASE module; it cannot fall back to 100 Mbps, so the manual speed 100 command is rejected or forces an unsupported mode. Half duplex is also not supported on 1000BASE-X fiber links, which require full duplex at 1 Gbps. Additionally, keeping the existing SFP fails the 2 km link budget (1000BASE-SX only reaches 550 m), so even if the interface came up, the link would not work at the required distance.
- ✗
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?”
Go deeper
Related to this question
Learn chapter
Half-Duplex vs Full-Duplex
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.