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Question

Difficulty: EasyInterface and Cable Troubleshooting Issues

Match each Cisco IOS interface status or error counter symptom to its corresponding physical or data-link troubleshooting root cause.

  • High number of late collisions recorded on a half-duplex configured interfaceDuplex mismatch between the connected local and remote switch ports
  • High number of CRC / FCS error counters increasing on the interfacePhysical cable corruption, excessive EMI noise, or loose connector
  • Interface state shows 'GigabitEthernet0/1 is up, line protocol is down'Layer 2 encapsulation mismatch or missing keepalive signals
  • Interface state shows 'FastEthernet0/1 is administratively down, line protocol is down'The port is disabled by default or configured with the 'shutdown' command

Answer

Late collisions match duplex mismatch; CRC errors match physical cable corruption or noise; Interface up / line protocol down matches Layer 2 encapsulation mismatch; Interface administratively down matches the interface being disabled with the shutdown command.
Matching interface symptoms correctly pairs late collisions with duplex mismatches, CRC error increments with physical cabling damage or electrical noise, 'up/down' status with Layer 2 framing/encapsulation issues, and 'administratively down' status with the interface shutdown configuration command.

Step-by-Step Solution

1
Examine the Layer 1 physical symptoms and Cisco IOS interface counters.
Differentiate between physical layer errors (CRC, late collisions), interface operational states (up/down), and administrative states (administratively down).
Each Cisco IOS interface statistic isolates specific Layer 1 or Layer 2 network faults.
2
Map each interface symptom to its underlying root cause.
Pair late collisions with duplex mismatch, CRC errors with cable/interference issues, up/down line protocol with encapsulation/keepalive failures, and administratively down with the shutdown command.
Accurate pairing ensures effective troubleshooting of physical and data link layer issues.

Key Concept

Cisco IOS Interface Troubleshooting and Diagnostics
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Topics

Interface and Cable Troubleshooting Issues

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