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220-1201 Practice Question: Connect a new router to a cable modem using an…
A technician needs to connect a new router to a cable modem using an Ethernet cable. The modem has an RJ45 port, and the router has an RJ45 WAN port. Which cable type should be used for this connection?
⚠ Common exam trap
The trap is overthinking auto-MDI/X and selecting crossover, or confusing rollover (console) with straight-through — candidates often mix up cable types when the devices are dissimilar.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Straight-through cable
A straight-through cable is used to connect devices that operate at different layers of the OSI model, such as a router (Layer 3) to a modem (Layer 2/1). The router's WAN port and the modem's RJ45 port are both MDI-X or auto-MDI/X, but the standard practice for connecting a router to a modem is a straight-through cable because they are dissimilar devices. Modern devices often support auto-MDI/X, but the exam expects the traditional rule.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Rollover cable
Why it's wrong here
A rollover cable, also known as a console cable, features a specific pinout where the pins on one end are completely reversed compared to the other end (e.g., pin 1 to 8, pin 2 to 7). This specialized wiring is exclusively designed for out-of-band management, connecting a computer's serial port (or USB-to-serial adapter) to a router or switch's console port for command-line configuration and troubleshooting. It is not designed for, nor capable of, transmitting standard Ethernet data between network devices.
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Crossover cable
Why it's wrong here
A crossover cable is specifically wired to swap the transmit (TX) and receive (RX) pairs between the two connected devices. This unique configuration allows two devices of the same type, such as two computers or two network switches, to communicate directly without an intervening hub or switch that would typically perform the signal crossover internally. Connecting a modem to a router, which are considered different types of devices in this context, typically requires a straight-through cable, as one device's TX should connect directly to the other's RX.
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Straight-through cable
Why this is correct
A straight-through Ethernet cable maintains the same pinout configuration on both ends, meaning pin 1 on one connector connects to pin 1 on the other, pin 2 to pin 2, and so on. This wiring scheme is the standard for connecting devices of different types, where one device's transmit (TX) pins are designed to connect directly to the other device's receive (RX) pins. Therefore, it is the correct choice for linking a modem (Data Communications Equipment) to a router (Data Terminal Equipment) for establishing network connectivity.
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Fiber optic cable
Why it's wrong here
Fiber optic cables transmit data using light pulses through glass or plastic strands, offering high bandwidth and immunity to electromagnetic interference. They utilize specialized connectors such as LC, SC, or ST, and require corresponding optical transceivers on network devices to convert electrical signals to light and vice versa. Standard modems and consumer-grade routers typically feature RJ45 Ethernet ports, which are designed for copper cabling, making fiber optic cables incompatible for a direct connection in this scenario without specialized media converters.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.