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Difficulty: MediumPhysical Interface and Cabling Types

A network technician needs to connect a workstation's Ethernet network interface card directly to a Cisco router's GigabitEthernet interface for initial device staging without using an intermediate switch. Auto-MDIX has been manually disabled on the router interface. Which cable type is required to successfully establish Layer 1 link integrity between these two devices?

  1. A crossover cable with all four wire pairs transposed between opposing connectorsAnswer
  2. B
    A standard straight-through cable, because workstations and router interfaces naturally use opposing MDI and MDI-X pinouts
  3. C
    A rollover cable terminated with RJ-45 connectors on both ends
  4. D
    A crossover cable with only pin pairs 1/2 and 3/6 transposed

Answer

A crossover cable with all four wire pairs transposed between opposing connectors
The correct option is the choice describing a crossover cable with all four wire pairs transposed. Ethernet interfaces on end-user PCs and routers both use standard MDI pinouts. When connecting two MDI devices directly without an intervening switch (MDI-X) and with Auto-MDIX disabled, the physical transmit conductors of one device must connect to the receive conductors of the other. Furthermore, 1000BASE-T GigabitEthernet utilizes all four wire pairs for data, requiring all four pairs to be crossed over.

Step-by-Step Solution

1
Identify the pinout role (MDI vs MDI-X) of each connected device
Both the host workstation NIC and the Cisco router interface are classified as MDI (Media Dependent Interface) devices.
MDI devices transmit data on specific pins and receive on others. Like devices (MDI-to-MDI or MDIX-to-MDIX) transmit on the same pins.
2
Determine the required cable configuration based on Auto-MDIX state
Because Auto-MDIX is disabled, a crossover cable must be used to swap the transmit and receive line pairs.
Without Auto-MDIX automatically remapping signals in hardware, a straight-through cable results in transmit signals connecting directly to transmit signals on the opposite end.
3
Account for the interface speed specification (GigabitEthernet / 1000BASE-T)
All four wire pairs (1/2, 3/6, 4/5, 7/8) must be transposed.
Unlike 10/100 Mbps Ethernet which uses two pairs, 1000BASE-T operates over all four copper pairs simultaneously.

Key Concept

MDI/MDI-X pinouts and 1000BASE-T crossover requirements
Estimated Time:1m 0s
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Topics

Physical Interface and Cabling Types

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