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Difficulty: HardPhysical Interface and Cabling Types

A network administrator is interconnecting two legacy Cisco routers directly using their GigabitEthernet0/0 interfaces (both configured as MDI ports) in a high-security environment where Auto-MDIX is manually disabled. The administrator needs to build a custom RJ-45 copper patch cable to achieve a functional 1000BASE-T connection between the devices. If the first end of the cable is terminated using the standard T568B pinout, which pin wiring scheme must be applied to the second end to guarantee full Gigabit Ethernet Layer 1 operation?

  1. Pins 1 and 2 crossed with pins 3 and 6, and pins 4 and 5 crossed with pins 7 and 8Answer
  2. B
    Pins 1 and 2 crossed with pins 3 and 6, while pins 4, 5, 7, and 8 remain wired straight through
  3. C
    Pins 1 and 2 crossed with pins 4 and 5, and pins 3 and 6 crossed with pins 7 and 8
  4. D
    Pins 1, 2, 3, 4, 5, 6, 7, and 8 wired straight through in identical pin-to-pin order on both ends

Answer

Pins 1 and 2 crossed with pins 3 and 6, and pins 4 and 5 crossed with pins 7 and 8
For Gigabit Ethernet (1000BASE-T) links between two MDI devices (such as routers) where Auto-MDIX is turned off, a full 4-pair crossover cable is required. This configuration crosses Pair 1 (pins 1 and 2) with Pair 2 (pins 3 and 6), as well as Pair 3 (pins 4 and 5) with Pair 4 (pins 7 and 8).

Step-by-Step Solution

1
Identify the device roles and interface pinout mode (MDI vs MDI-X).
Both router GigabitEthernet interfaces act as MDI (Medium Dependent Interface) ports.
Like devices (router to router, switch to switch) require pin crossover on the cable when connected directly without Auto-MDIX.
2
Determine the physical medium transmission standard requirements (1000BASE-T).
1000BASE-T operates over Category 5e/6 UTP using all four pairs (8 wires) simultaneously for full-duplex transmission (BI_DA, BI_DB, BI_DC, BI_DD).
Unlike 10BASE-T/100BASE-TX which only utilize pairs 1-2 and 3-6, 1000BASE-T requires all four pairs to be properly paired and crossed.
3
Map the crossover pinout required for 1000BASE-T operation.
Pair 1 (pins 1, 2) swaps with Pair 2 (pins 3, 6), and Pair 3 (pins 4, 5) swaps with Pair 4 (pins 7, 8).
This guarantees that transmit and receive signals across all four bi-directional channels align correctly between the two MDI interfaces.

Key Concept

1000BASE-T Crossover Cabling Pinouts and MDI/MDI-X Interconnection
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Topics

Physical Interface and Cabling Types

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