- A
The modem's firmware was corrupted during the outage.
Why wrong: Firmware corruption from a power outage is rare; modems are designed to recover from power loss.
- B
The coaxial cable was damaged by the power surge.
Why wrong: Coaxial cable is passive and unlikely to be damaged by a power surge; surge damage typically affects electronics.
- C
The modem is re-establishing its connection to the ISP.
After power loss, the modem must re-sync with the cable headend, which is indicated by a blinking online light.
- D
The router's DHCP server failed.
Why wrong: The blinking online light is a modem issue, not a router issue; DHCP would affect local IP assignment, not the modem's sync status.
Question 917 of 1,020
Troubleshooting Cable Modem Blinking Online Light After Power Outage
This 220-1201 practice question tests your understanding of internet connection types. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The correct answer is that the modem is re-establishing its connection to the ISP. After a power outage, a cable modem loses its synchronization with the provider’s headend, and the blinking online light indicates it is actively scanning for and negotiating a signal lock with the upstream and downstream channels. This process, called ranging and registration, can take several minutes as the modem authenticates and receives a new IP address from the ISP’s DHCP server. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of ISP connectivity fundamentals and the difference between local power status (solid power light) and WAN link state (blinking online light). A common trap is to assume the modem is faulty or that the coax cable is damaged, but the key clue is the power outage itself—if the power light is steady, the modem is receiving electricity and the issue is upstream. Remember the memory tip: “Blinking online after blackout? Give it time to check in.”
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Firmware corruption from a power outage is rare; modems are designed to recover from power loss.
- ✗
The coaxial cable was damaged by the power surge.
Why it's wrong here
Coaxial cable is passive and unlikely to be damaged by a power surge; surge damage typically affects electronics.
- ✓
The modem is re-establishing its connection to the ISP.
Why this is correct
After power loss, the modem must re-sync with the cable headend, which is indicated by a blinking online light.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The router's DHCP server failed.
Why it's wrong here
The blinking online light is a modem issue, not a router issue; DHCP would affect local IP assignment, not the modem's sync status.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
During DOCSIS initialization, the modem scans for downstream channels, synchronizes with the QAM signal, and then performs upstream ranging to adjust transmit power and timing offsets. The blinking 'online' light corresponds to the 'ranging' and 'DHCP' stages of the DOCSIS startup process (T3 and T4 timeouts). In a real-world scenario, if the power outage was brief, the modem may still be in its 'warm start' state and will re-establish the connection faster, but a longer outage forces a full cold-start re-initialization, which can take 2–5 minutes.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Internet Connection Types — This question tests Internet Connection Types — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 220-1201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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