CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
You are connected to R1. The network administrator reports that hosts on VLAN 10 cannot communicate with the server attached to R2's GigabitEthernet0/1 interface. Troubleshoot and resolve the issue. Identify the root cause and apply the necessary fix on R1.
⚠ Common exam trap
The exam trap is that candidates often focus on speed mismatches or clearing counters, but the real issue is duplex mismatch. Remember that on GigabitEthernet interfaces, auto-negotiation is the default and recommended setting; static duplex/speed settings can cause mismatches and errors.
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 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.
The issue is a duplex mismatch on GigabitEthernet0/0. R1 is configured with 'duplex full' and 'speed 1000', but the connected switch port is likely set to auto-negotiate or is set to half-duplex. This causes high input errors (1500) and degraded performance. The fix is to set R1's G0/0 to auto-negotiate both speed and duplex, matching the switch's configuration. Enter interface configuration mode for G0/0, issue 'no duplex' and 'no speed' to revert to auto, then clear the interface counters with 'clear counters gigabitethernet0/0'.
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 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.
Why this is correct
This is correct because the issue is a duplex mismatch on GigabitEthernet0/0. R1 is statically set to full duplex and 1000 Mbps, but the connected switch port likely uses auto-negotiation or half-duplex, causing input errors. Reverting to auto-negotiation with 'no duplex' and 'no speed' allows both sides to negotiate the best settings, resolving the mismatch.
- ✗
Change the duplex setting on GigabitEthernet0/0 to half-duplex using 'duplex half'.
Why it's wrong here
This is incorrect because forcing half-duplex on R1's GigabitEthernet0/0 would likely cause a mismatch if the switch is set to full duplex or auto-negotiation, worsening the problem. The correct approach is to enable auto-negotiation on both sides.
- ✗
Apply 'speed 100' and 'duplex full' on GigabitEthernet0/0 to match a common switch configuration.
Why it's wrong here
This is incorrect because the interface is GigabitEthernet, which typically requires 1000 Mbps. Forcing 100 Mbps and full duplex may not be supported or could cause a speed mismatch. Additionally, the root cause is duplex mismatch, not speed.
- ✗
Clear the interface counters on GigabitEthernet0/0 with 'clear counters gigabitethernet0/0' without changing any configuration.
Why it's wrong here
Clearing counters on GigabitEthernet0/0 is purely a statistical reset operation; it zeroes the input errors, CRC, and runt counters but does not modify any interface setting such as duplex or speed. Because the underlying duplex mismatch remains unaddressed, the interface will immediately and continuously re-accumulate input errors and late collisions, so the symptom persists. This command is useful for post-fix verification, not for troubleshooting the root cause, and it does not trigger any link renegotiation or physical-layer reconfiguration.
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 'no duplex' and 'no speed' under interface GigabitEthernet0/0 to enable auto-negotiation.Correct answer▾
Why this is correct
This is correct because the issue is a duplex mismatch on GigabitEthernet0/0. R1 is statically set to full duplex and 1000 Mbps, but the connected switch port likely uses auto-negotiation or half-duplex, causing input errors. Reverting to auto-negotiation with 'no duplex' and 'no speed' allows both sides to negotiate the best settings, resolving the mismatch.
✗Change the duplex setting on GigabitEthernet0/0 to half-duplex using 'duplex half'.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that manually setting half-duplex does not resolve a mismatch; it may create a new mismatch or degrade performance further.
Why candidates choose this
Candidates might think that since the switch is half-duplex, setting the router to half-duplex will match, but they overlook that the switch may be auto-negotiating or that the router's current full-duplex setting is the problem.
✗Apply 'speed 100' and 'duplex full' on GigabitEthernet0/0 to match a common switch configuration.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that GigabitEthernet interfaces usually operate at 1000 Mbps; setting speed to 100 may cause the interface to not come up or to underperform.
Why candidates choose this
Candidates might think that lowering the speed to 100 Mbps and setting full duplex is a safe fallback, but this ignores the interface's capabilities and the actual issue of duplex mismatch.
✗Clear the interface counters on GigabitEthernet0/0 with 'clear counters gigabitethernet0/0' without changing any configuration.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that clearing counters is a diagnostic step, not a fix. The root cause (duplex mismatch) remains unaddressed.
Why candidates choose this
Candidates might think that clearing counters resolves the issue because it temporarily removes the error count, but they fail to recognize that the problem persists.
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?”
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Related to this question
Learn chapter
Network Topology Types
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
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.