- A
show interfaces diagnostics optics
Why wrong: This command is specific to optical interfaces and shows optical parameters like laser bias, temperature, etc. It does not show detailed error counters.
- B
show interfaces detail
Why wrong: 'show interfaces detail' also shows some error counters, but not as extensive as 'show interfaces extensive'. The extensive output includes more granular error types.
- C
show interfaces extensive
'show interfaces extensive' provides detailed statistics per interface, including input errors such as CRC, framing, runts, and output errors. It is the best command for hardware error analysis.
- D
show log messages
Why wrong: 'show log messages' displays system log entries. While interface errors may appear in logs, it does not provide structured, per-interface error counters.
Quick Answer
The answer is the 'show interfaces extensive' command, because it provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command drills down into the physical layer statistics, exposing per-interface input and output errors that reveal whether faulty cabling, transceivers, or line cards are causing data corruption. On the JNCIA-Junos exam, you will be tested on distinguishing this command from less detailed options like 'show interfaces terse' or 'show interfaces detail', which omit the granular hardware error breakdown. A common trap is assuming 'show interfaces' alone suffices, but it lacks the specific counters for frame, runts, giants, and CRC errors needed for hardware troubleshooting. Remember the mnemonic: “Extensive equals exhaustive errors” — when you suspect hardware, go extensive to catch every CRC and runt.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. 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 network engineer suspects a hardware issue on an interface. Which command provides the most detailed hardware error counters, including CRC errors, framing errors, and runts?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"which command"Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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
show interfaces extensive
The 'show interfaces extensive' command provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command displays per-interface statistics at the physical layer, such as input errors, output errors, and specific error types like frame, runts, giants, and CRC errors, which are essential for diagnosing hardware issues.
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.
- ✗
show interfaces diagnostics optics
Why it's wrong here
This command is specific to optical interfaces and shows optical parameters like laser bias, temperature, etc. It does not show detailed error counters.
- ✗
show interfaces detail
Why it's wrong here
'show interfaces detail' also shows some error counters, but not as extensive as 'show interfaces extensive'. The extensive output includes more granular error types.
- ✓
show interfaces extensive
Why this is correct
'show interfaces extensive' provides detailed statistics per interface, including input errors such as CRC, framing, runts, and output errors. It is the best command for hardware error analysis.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
show log messages
Why it's wrong here
'show log messages' displays system log entries. While interface errors may appear in logs, it does not provide structured, per-interface error counters.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'show interfaces detail' with 'show interfaces extensive', assuming 'detail' provides the most granular error counters, but only 'extensive' includes the full hardware error breakdown required for hardware fault diagnosis.
Trap categories for this question
Command / output trap
This command is specific to optical interfaces and shows optical parameters like laser bias, temperature, etc. It does not show detailed error counters.
Detailed technical explanation
How to think about this question
The 'show interfaces extensive' command in Junos outputs a comprehensive set of counters at the physical and link layers, including the 'Input errors' field which breaks down into CRC errors, framing errors, runts, giants, and other physical-layer anomalies. These counters are directly read from the hardware (e.g., ASIC or FPGA) and are critical for isolating faulty cables, SFPs, or interface hardware. In real-world scenarios, a high count of CRC errors with no framing errors often points to a bad cable or SFP, while framing errors may indicate clocking or line code violations.
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 JNCIA-JUNOS 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.
- →
Operational Monitoring and Maintenance — study guide chapter
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: show interfaces extensive — The 'show interfaces extensive' command provides the most detailed hardware error counters for a Junos interface, including CRC errors, framing errors, and runts. This command displays per-interface statistics at the physical layer, such as input errors, output errors, and specific error types like frame, runts, giants, and CRC errors, which are essential for diagnosing hardware issues.
What should I do if I get this JNCIA-JUNOS 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: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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