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Difficulty: MediumPhysical Interface and Cabling Types

A network administrator needs to perform the initial configuration on a new Cisco Catalyst switch via an out-of-band management session. The administrator connects a laptop terminal emulator directly to the RJ-45 console port of the switch using an RS-232 serial cable adapter. Which cable pinout scheme is required to correctly map the laptop terminal adapter signals to the switch console interface?

  1. A rollover cable pinout where pin 1 on one connector connects to pin 8 on the opposite connector.Answer
  2. B
    A straight-through cable pinout adhering to T568B specifications on both connector ends.
  3. C
    A two-pair crossover cable pinout swapping pin 1 with pin 3 and pin 2 with pin 6.
  4. D
    A four-pair crossover cable pinout swapping pins 1/3, 2/6, 4/7, and 5/8.

Answer

A rollover cable pinout (where pin 1 connects to pin 8, pin 2 to pin 7, etc.) is required to connect a terminal serial interface to a Cisco switch RJ-45 console port.
Cisco RJ-45 console ports require a rollover cable (often called a console cable). In a rollover cable, the pinout on one end is completely inverted relative to the other end—pin 1 maps to pin 8, pin 2 maps to pin 7, pin 3 maps to pin 6, and pin 4 maps to pin 5. When combined with an RS-232 terminal adapter (DB-9 or USB-to-serial), this pin inversion routes the laptop serial transmitter pin to the console receiver pin and vice versa.

Step-by-Step Solution

1
Identify the type of connection being established.
The connection is an out-of-band management terminal connection between a host PC/laptop terminal adapter and an RJ-45 Cisco console port, not an Ethernet network data link.
Console management uses asynchronous RS-232 serial signalling over an RJ-45 physical port interface rather than standard Ethernet framing.
2
Determine the physical pin mapping for Cisco RJ-45 console interfaces.
Cisco console ports use a rollover pinout convention where the wire sequence completely reverses from one RJ-45 connector to the other end (Pin 1 to Pin 8, Pin 2 to Pin 7, Pin 3 to Pin 6, Pin 4 to Pin 5).
This reversal correctly aligns the Transmit Data (TxD), Receive Data (RxD), and Ground signals between the RJ-45 console port and the DB-9 / USB serial adapter attached to the management PC.

Key Concept

Cisco Console Port and Rollover Cable Pinouts
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Topics

Physical Interface and Cabling Types

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