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Difficulty: MediumInterface and Cable Troubleshooting Issues

A network administrator is troubleshooting poor file transfer performance on a switch interface connected to an enterprise application server. The administrator executes the `show interfaces gigabitethernet 0/1` command on the switch and receives the following CLI output:

GigabitEthernet0/1 is up, line protocol is up
Hardware is GigabitEthernet, address is 0007.ec29.2101
Full-duplex, 100Mb/s, media type is 100BaseTX
12458 input errors, 12458 CRC, 0 frame, 0 overrun, 0 ignored
0 output errors, 45211 collisions, 1204 late collision, 0 deferred

Based on this output, what is the most likely cause of the interface errors?

  1. A duplex mismatch between the switch port and the connected server interfaceAnswer
  2. B
    An incorrect Ethernet cable pinout type connecting the switch to the server
  3. C
    A native VLAN configuration mismatch between the switch and the connected host
  4. D
    A misinterpretation of remote neighbor TLV statistics received from Layer 2 discovery protocols

Answer

A duplex mismatch between the switch port and the connected server interface
A duplex mismatch occurs when one end of an Ethernet segment is configured for full-duplex while the opposite end operates in half-duplex mode. Because full-duplex mode disables CSMA/CD collision detection, the full-duplex side transmits data whenever ready. The half-duplex side, which is actively listening for carrier sense, experiences collisions and late collisions during its transmissions. The full-duplex side receives colliding signals mid-transmission, registering them as input CRC errors.

Step-by-Step Solution

1
Analyze the interface status and line protocol state.
The link status is 'up/up', proving Layer 1 signaling and Layer 2 framing are established.
Eliminates total physical disconnection or wrong pinout issues that prevent link activation.
2
Examine the duplex settings and error counters in the CLI output.
The interface reports 'Full-duplex' along with non-zero 'collisions', 'late collision', and 'CRC' errors.
In true full-duplex operation, collisions should never occur because transmit and receive pathways are independent.
3
Correlate late collisions and CRC errors to physical layer operations.
Late collisions occur when the remote half-duplex side detects a collision after the slot time because the local full-duplex side transmits without checking CSMA/CD carrier sense.
This symptom pattern unequivocally points to a duplex mismatch between the two connected devices.

Key Concept

Duplex Mismatch Symptoms and Error Counters
Estimated Time:1m 30s
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Topics

Interface and Cable Troubleshooting Issues

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