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220-1201 Practice Question: A user's cable internet goes out completely after…
A user's cable internet goes out completely after a power outage. The modem's power light is on, but the 'online' light is blinking. What is the most likely issue?
⚠ Common exam trap
The CompTIA A+ exam often tests the misconception that a blinking light always indicates a hardware failure or corruption, when in fact it is a standard operational state during reconnection after a power loss.
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
✓
The modem is re-establishing its connection to the ISP.
After a power outage, the modem's power light being on indicates it has power, but the blinking 'online' light shows it has lost its upstream connection to the ISP. Cable modems use DOCSIS (Data Over Cable Service Interface Specification) to establish a link with the Cable Modem Termination System (CMTS). The blinking online light is the standard behavior during the re-initialization and ranging process, which can take several minutes as the modem negotiates frequencies, timing, and power levels with the CMTS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The modem's firmware was corrupted during the outage.
Why it's wrong here
While possible in extreme cases, modern modems store firmware in non-volatile memory (e.g., flash memory) which is not typically affected by sudden power loss. They are designed with robust power loss recovery mechanisms and checksum verification, making firmware corruption during a simple power outage an extremely rare occurrence, especially compared to the common need for re-synchronization. Such corruption would likely render the modem inoperable, not merely cause a blinking online light.
- ✗
The coaxial cable was damaged by the power surge.
Why it's wrong here
Coaxial cable is a passive transmission medium, primarily composed of a copper conductor, dielectric insulator, and shielding. It does not contain active electronic components susceptible to overvoltage or current spikes from a power surge. Power surges typically damage the sensitive active electronic circuits within devices like modems, routers, or computers, not the robust, passive cabling itself, which is designed for signal transmission and is highly resistant to electrical damage.
- ✓
The modem is re-establishing its connection to the ISP.
Why this is correct
Following a power outage, a cable modem must complete a full boot sequence and re-establish communication with the Internet Service Provider's (ISP) cable modem termination system (CMTS). This involves a multi-step process including ranging, acquiring downstream and upstream channels, and obtaining an IP address via DHCP. A blinking "Online" or "Internet" light typically indicates that the modem is actively attempting to synchronize and register with the ISP's network, which is a normal and expected behavior after a power cycle.
- ✗
The router's DHCP server failed.
Why it's wrong here
A router's DHCP server is responsible for assigning local IP addresses to devices *within* the local area network (LAN), such as computers, phones, or other network clients, enabling them to communicate internally. It does not play a role in the cable modem's ability to establish or maintain its external connection to the Internet Service Provider (ISP). A blinking "Online" light on the modem specifically indicates an issue with the modem's external WAN connection, independent of the router's internal LAN functions.
Go deeper
Related to this question
Learn chapter
Internet Connection Types
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
Key term
Cable internet
Cable internet is a type of broadband internet access that uses the same coaxial copper cables as cable television to deliver high-speed data to homes and businesses.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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