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Difficulty: MediumInterface and Cable Troubleshooting Issues

A network administrator is troubleshooting poor throughput on a switch port connected to a server. Running the show interfaces command reveals a rapidly incrementing counter for cyclic redundancy check (CRC) errors alongside late collisions. Which TWO issues are the most likely root causes of these interface statistics? (Select two.)

  1. A duplex mismatch between the switch port and the connected server interface.Answer
  2. Physical layer noise or damage on the copper Ethernet cable connection.Answer
  3. C
    A native VLAN mismatch configured on the trunk link between the switch and the host.
  4. D
    An incorrect Ethernet pinout selection preventing link status initialization.

Answer

The most likely root causes are a duplex mismatch between the switch port and the connected device, and physical layer noise or damage on the Ethernet cable connection.
Late collisions typically indicate a duplex mismatch where one end operates in full-duplex mode while the other operates in half-duplex mode. CRC errors indicate corrupted frames resulting from electrical interference, loose connectors, bad cable shielding, or damaged media.

Step-by-Step Solution

1
Analyze the reported interface error counters (CRC errors and late collisions).
Identify that late collisions occur when collisions are detected after the first 64 bytes of a frame have been transmitted, while CRC errors indicate frame corruption during transit.
Understanding what layer these counters operate on isolates the issue to Layer 1 (physical) and Layer 2 (data link speed/duplex negotiation).
2
Evaluate potential causes for late collisions.
A duplex mismatch (one side set to full-duplex and the other to half-duplex) causes the half-duplex side to transmit while receiving data, generating late collisions.
Late collisions are classic symptoms of duplex mismatches or excessive cable lengths exceeding maximum Ethernet distance standards.
3
Evaluate potential causes for CRC (Cyclic Redundancy Check) errors.
CRC errors occur when the checksum computed by the receiving interface does not match the checksum frame check sequence (FCS) sent by the transmitter, typical of faulty cabling or bad connectors.
Physical medium flaws cause electrical noise and flipped bits during frame transmission.

Key Concept

Interface Error Statistics & Duplex Mismatches
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Topics

Interface and Cable Troubleshooting Issues

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