In Ethernet LANs, which statement best summarizes the correct use of straight-through, crossover, and rolled (rollover) UTP cables?

Introduction / Context:
Understanding different types of Ethernet cabling and their proper applications is a fundamental networking skill. Before auto MDI or MDIX became common, the distinction between straight-through and crossover cables was critical for making correct physical connections. Rolled cables serve an entirely different purpose, primarily for device management.

Given Data / Assumptions:

• We are dealing with RJ45 UTP copper cables in Ethernet networks and for console access.
• Device types include hosts, switches, routers, and console ports.
• We assume some older equipment may not support auto MDI or MDIX, so correct cable choice matters.

Concept / Approach:
In traditional Ethernet wiring, straight-through cables connect devices that use opposite transmit and receive pairs, such as a host network interface card to a switch port or a switch to a router. Crossover cables swap the transmit and receive pairs, making them appropriate for connecting similar devices such as switch to switch, hub to hub, or host to host. Rolled cables reverse all the pins and are used to carry serial console signals between a PC and a network device's console port, not to carry Ethernet frames.

Step-by-Step Solution:
Step 1: Identify that straight-through cables keep pin 1 to pin 1, pin 2 to pin 2, and so on, making them suitable for host to switch and switch to router connections.Step 2: Recognize that crossover cables swap the transmit and receive pairs, connecting pin 1 on one end to pin 3 on the other and pin 2 to pin 6, which is needed when similar devices are connected without an intermediate switch.Step 3: Understand that rolled cables map pin 1 to pin 8, pin 2 to pin 7, and so forth, producing a complete reversal. This wiring is designed for RS-232 style serial console connections, not for Ethernet data.Step 4: Conclude that each cable type has a distinct role: straight-through for most access links, crossover for back-to-back connections of similar devices (if auto MDI or MDIX is not present), and rollover for console management.

Verification / Alternative check:
Network lab manuals and Cisco documentation typically include diagrams that show which cable to use for each device pairing. These diagrams consistently match the summary in option A, differentiating data cables from console rollover cables.

Why Other Options Are Wrong:
Option B incorrectly ties cable type to duplex mode, which is unrelated to the physical wiring of the pairs.Option C mischaracterizes straight-through cables as WAN only and claims rolled cables are obsolete, which is incorrect.Option D is wrong because the internal wiring of straight-through, crossover, and rolled cables differs, and using the wrong type can prevent devices from linking or communicating.

Common Pitfalls:
Students often confuse crossover and rolled cables because both look like standard patch leads. Remembering that rollover cables are primarily for console access and that crossover cables are for similar device data links helps avoid miswiring in the lab.

Final Answer:
The best summary is that Straight-through cables connect different device types such as host to switch or switch to router, crossover cables connect similar device types such as switch to switch or host to host, and rolled cables are used only for console connections, not for Ethernet data links.