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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. 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
G0/0192.0.2.1/30G0/0192.0.2.2/30linkR1R2

You are troubleshooting connectivity between R1 and R2. The link is up but users report intermittent packet loss. Examine the provided show interface output on R1, identify the root cause, and apply the necessary fix to restore normal operation.

Question 1hardTroubleshooting
Full question →

Exhibit

R1# show interfaces GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
  Hardware is ISR4331-2x1GE, address is aabb.cc00.0100 (bia aabb.cc00.0100)
  Internet address is 192.0.2.1/30
  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)
  Full-duplex, 1000Mb/s, link type is auto, media type is RJ45
  output flow-control is unsupported, input 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 12000 bits/sec, 12 packets/sec
  5 minute output rate 8000 bits/sec, 8 packets/sec
     12034 packets input, 1234567 bytes, 0 no buffer
     Received 12034 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     150 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     45678 packets output, 4567890 bytes, 0 underruns
     0 output errors, 0 collisions, 2 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#

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 'duplex auto' and 'speed auto' on interface G0/0 of R1.

The interface shows 'input errors' (150) but zero CRC and zero frame errors. This combination, along with 'Full-duplex, 1000Mb/s' and the link being up/up, indicates the interface is manually set to full-duplex while the connected device (R2) is likely operating at half-duplex (duplex mismatch). Although CRC errors are zero, input errors can still occur due to collisions on a mismatched duplex link. The fix is to set the interface to auto-negotiate duplex and speed, or to manually set both sides to the same duplex setting. The recommended command is 'duplex auto' and 'speed auto' on both ends. In this scenario, we will configure R1's G0/0 for auto-negotiation.

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.

  • ✓

    Configure 'duplex auto' and 'speed auto' on interface G0/0 of R1.

    Why this is correct

    This is correct because the symptoms (input errors with zero CRC/frame errors, full-duplex manually set) indicate a duplex mismatch. Enabling auto-negotiation on both ends allows the devices to agree on duplex and speed, resolving the mismatch and eliminating collisions that cause input errors.

    Related concept

    Static NAT maps one inside address to one outside address.

  • ✗

    Replace the faulty cable between R1 and R2.

    Why it's wrong here

    This is incorrect because the interface is up/up and there are no CRC or frame errors, which would typically indicate a physical layer issue like a faulty cable. The input errors without CRC suggest a duplex mismatch, not a cabling problem.

  • ✗

    Increase the MTU size on interface G0/0 of R1.

    Why it's wrong here

    This is incorrect because increasing MTU would not resolve duplex mismatch issues. MTU affects the maximum packet size, and changing it could cause fragmentation problems or mismatches with the neighbor, worsening connectivity.

  • ✗

    Disable CDP on interface G0/0 of R1.

    Why it's wrong here

    This is incorrect because CDP (Cisco Discovery Protocol) is a Layer 2 protocol used for neighbor discovery and does not affect duplex or speed settings. Disabling CDP would not fix the duplex mismatch causing input errors.

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 'duplex auto' and 'speed auto' on interface G0/0 of R1.Correct answer▾

Why this is correct

This is correct because the symptoms (input errors with zero CRC/frame errors, full-duplex manually set) indicate a duplex mismatch. Enabling auto-negotiation on both ends allows the devices to agree on duplex and speed, resolving the mismatch and eliminating collisions that cause input errors.

✗Replace the faulty cable between R1 and R2.Wrong answer — click to see why▾

Why this is wrong here

A faulty cable would likely cause CRC errors, frame errors, or interface resets, not just input errors with zero CRC.

Why candidates choose this

Candidates often assume packet loss is due to a bad cable, especially when the link is up but experiencing errors.

✗Increase the MTU size on interface G0/0 of R1.Wrong answer — click to see why▾

Why this is wrong here

MTU size does not affect duplex negotiation or collisions; it is unrelated to the input errors caused by duplex mismatch.

Why candidates choose this

Candidates might think larger MTU reduces overhead or errors, but it does not address the root cause.

✗Disable CDP on interface G0/0 of R1.Wrong answer — click to see why▾

Why this is wrong here

CDP has no impact on duplex negotiation or error counters; it is unrelated to the problem.

Why candidates choose this

Candidates might confuse CDP with other protocols that affect interface behavior, or think disabling CDP reduces overhead and errors.

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: Configure 'duplex auto' and 'speed auto' on interface G0/0 of R1. — The interface shows 'input errors' (150) but zero CRC and zero frame errors. This combination, along with 'Full-duplex, 1000Mb/s' and the link being up/up, indicates the interface is manually set to full-duplex while the connected device (R2) is likely operating at half-duplex (duplex mismatch). Although CRC errors are zero, input errors can still occur due to collisions on a mismatched duplex link. The fix is to set the interface to auto-negotiate duplex and speed, or to manually set both sides to the same duplex setting. The recommended command is 'duplex auto' and 'speed auto' on both ends. In this scenario, we will configure R1's G0/0 for auto-negotiation.

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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