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An IT technician is troubleshooting a newly installed network drop in an industrial facility. A workstation connected to a Gigabit Ethernet switch experiences severe packet loss and fails to reach expected throughput. Testing the cable run with a wiremap tester reveals that the wall outlet end is wired to the T568B standard, while the patch panel end is wired to the T568A standard. The switch port LED displays a solid link at 100 Mbps, but the switch port log reports excessive Frame Check Sequence (FCS) errors and late collisions during transmission. Which of the following best describes the root cause of this issue and the appropriate corrective action?

  1. The mismatch between T568A and T568B creates an Ethernet crossover pinout that prevents full 1000BASE-T auto-negotiation and causes signal cross-talk; re-terminate the patch panel end to T568B to create a uniform straight-through cable.Answer
  2. B
    Workstation-to-switch connections strictly require T568A crossover wiring; re-terminate the wall outlet end to T568A so both cable ends use crossover configuration.
  3. C
    The Layer 2 switch port lacks Layer 3 routing configuration to resolve speed mismatches across separate IP subnets; reconfigure the switch interface routing table.
  4. D
    The active 100 Mbps link light confirms full physical layer functionality, indicating the FCS errors stem from DNS daemon failures; clear the local client DNS resolver cache.

Answer

Re-terminating the patch panel end to match T568B resolves the pinout mismatch, restores a proper straight-through pin configuration across all four wire pairs, eliminates FCS errors, and allows the link to auto-negotiate at 1000BASE-T Gigabit speed.
Standard Ethernet patch and horizontal cable runs between host workstations and network switches require straight-through wiring, where both ends use the identical wiring standard (either T568A on both ends or T568B on both ends). Terminating T568A on one end and T568B on the other produces a crossover cable. In Gigabit Ethernet (1000BASE-T), all four pairs are used simultaneously. An improper pinout creates split pairs and crosstalk, leading to Frame Check Sequence (FCS) errors and preventing full-duplex Gigabit auto-negotiation. Re-terminating the patch panel end to T568B ensures a matching straight-through configuration.

Step-by-Step Solution

1
Analyze the wiremap tester output and wiring standards.
Identified that one end is wired as T568B and the opposing end as T568A.
Mixing T568A and T568B on opposite ends of a single cable run creates a crossover cable pinout (pins 1 & 2 swapped with pins 3 & 6).
2
Evaluate the symptom of 100 Mbps link speed with high FCS errors on a Gigabit link.
Determined that the crossover configuration and split pairs prevent 1000BASE-T auto-negotiation across all four cable pairs.
Gigabit Ethernet (1000BASE-T) relies on high-frequency bidirectional signaling on all 4 pairs; improper pair alignment causes severe NEXT (near-end crosstalk) and frame corruption.
3
Select the proper physical Layer 1 remediation step.
Re-terminate one end so both ends follow the same wiring standard (T568B to T568B).
Creating a uniform straight-through cable restores proper pair geometry and full 1000 Mbps auto-negotiation.

Key Concept

Ethernet Cable Termination Standards (T568A vs T568B) and Physical Layer Troubleshooting
Estimated Time:2m 0s
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