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.
Exhibit
Refer to the exhibit.
Oct 10 10:00:00 router mgd[1234]: UI_COMMIT: User 'admin' requested commit
Oct 10 10:00:05 router mgd[1234]: UI_COMMIT_PROGRESS: Commit operation in progress
Oct 10 10:00:10 router mib2d[5678]: SNMP_TRAP_LINK_DOWN: ifIndex 5, ifDescr ge-0/0/1
Oct 10 10:00:11 router mib2d[5678]: SNMP_TRAP_LINK_UP: ifIndex 5, ifDescr ge-0/0/1
Oct 10 10:00:15 router kernel: interface ge-0/0/1 link up
Oct 10 10:00:20 router kernel: interface ge-0/0/1 link down
Oct 10 10:00:25 router kernel: interface ge-0/0/1 link up
Sep 20 09:00:00 router mgd[1234]: UI_COMMIT: User 'config' requested commit
Refer to the exhibit. Based on the log output, what is the most likely issue with interface ge-0/0/1?
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.
Refer to the exhibit.
Oct 10 10:00:00 router mgd[1234]: UI_COMMIT: User 'admin' requested commit
Oct 10 10:00:05 router mgd[1234]: UI_COMMIT_PROGRESS: Commit operation in progress
Oct 10 10:00:10 router mib2d[5678]: SNMP_TRAP_LINK_DOWN: ifIndex 5, ifDescr ge-0/0/1
Oct 10 10:00:11 router mib2d[5678]: SNMP_TRAP_LINK_UP: ifIndex 5, ifDescr ge-0/0/1
Oct 10 10:00:15 router kernel: interface ge-0/0/1 link up
Oct 10 10:00:20 router kernel: interface ge-0/0/1 link down
Oct 10 10:00:25 router kernel: interface ge-0/0/1 link up
Sep 20 09:00:00 router mgd[1234]: UI_COMMIT: User 'config' requested commit
A
Interface is experiencing flapping
Repeated up/down events indicate flapping.
B
Interface is up and stable
Why wrong: Logs show instability.
C
Interface is administratively down
Why wrong: No evidence of admin down; link state changes imply physical issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Interface is experiencing flapping
The log output shows repeated 'link UP' and 'link DOWN' events for interface ge-0/0/1 within a short time window, which is the classic symptom of interface flapping. Flapping typically occurs due to physical layer issues such as faulty cables, damaged transceivers, or marginal signal integrity, causing the interface to continuously transition between up and down states.
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.
✓
Interface is experiencing flapping
Why this is correct
Repeated up/down events indicate flapping.
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.
✗
Interface is up and stable
Why it's wrong here
Logs show instability.
✗
Interface is administratively down
Why it's wrong here
No evidence of admin down; link state changes imply physical issue.
✗
Interface is configured incorrectly
Why it's wrong here
No configuration errors in logs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume any interface issue is configuration-related (Option D) or that a single 'link UP' message means the interface is stable (Option B), but the repeated pattern of alternating UP/DOWN events is the definitive indicator of flapping.
Trap categories for this question
Command / output trap
Logs show instability.
Detailed technical explanation
How to think about this question
Interface flapping is often detected by the Junos OS kernel, which logs each link state transition via the 'ifd' (interface device) process. The 'show log messages' output reveals the exact timestamps of these transitions; a high frequency (e.g., multiple events per minute) indicates a physical layer fault. In real-world scenarios, flapping can also be caused by auto-negotiation mismatches or faulty SFP modules, and the 'show interfaces diagnostics' command can help isolate the issue by checking optical power levels or error counters.
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 — 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: Interface is experiencing flapping — The log output shows repeated 'link UP' and 'link DOWN' events for interface ge-0/0/1 within a short time window, which is the classic symptom of interface flapping. Flapping typically occurs due to physical layer issues such as faulty cables, damaged transceivers, or marginal signal integrity, causing the interface to continuously transition between up and down states.
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: "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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Question Discussion
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