Question 194 of 514

Operational Monitoring and Maintenance →hardMultiple ChoiceObjective-mapped

SNMP Interface Flapping Detection

This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 company runs Juniper MX routers in a data center. They have a monitoring server that polls SNMP every 5 minutes. Recently, the monitoring server reported that interface ge-0/0/1 on router R1 has been down for 3 hours, but the network operations center says that no alarms were triggered and the link appears up from their end. The administrator logs into R1 and runs 'show interfaces ge-0/0/1' and sees that the interface is up with no errors, but the output shows 'Last flapped: 3 hours ago', which matches the monitoring downtime. Further investigation reveals that the interface has been administratively disabled and re-enabled at that time by an automated script that was later rolled back. The monitoring server uses ifAdminStatus and ifOperStatus OIDs. Which action would most reliably prevent this false positive in the future?

A
Use 'show interfaces extensive' to confirm interface status.
Why wrong: Using 'show interfaces extensive' is a manual verification step, not an automated monitoring solution. It does not prevent false positives in the automated SNMP-based monitoring system.
B
Change the SNMP polling interval to 1 minute.
Why wrong: Changing the SNMP polling interval to 1 minute would increase the frequency of checks but still cannot distinguish between a true link failure and an administrative state change. It does not address the root cause.
C
Monitor ifLastChange OID along with ifOperStatus to detect administrative flapping.
Monitoring the ifLastChange OID along with ifOperStatus allows the monitoring system to detect the timestamp of the last state change. If the ifLastChange time matches the ifAdminStatus change time, the monitoring system can identify that the interface was administratively disabled/enabled, preventing a false positive alert.
D
Disable the automated script that caused the administrative disable.
Why wrong: Disabling the automated script that caused the administrative disable is a temporary fix. It does not improve the monitoring system's ability to handle future administrative changes, which may occur from other sources.

Full breakdown with real-world context →

Quick Answer

The answer is to monitor the ifLastChange OID alongside ifOperStatus for reliable SNMP interface flapping detection. This is correct because ifLastChange provides the exact timestamp of the last state transition, allowing the monitoring system to cross-reference a down event with a recent change in ifAdminStatus, thereby distinguishing an administrative flap from a true link failure. On the JNCIA-Junos exam, this scenario tests your understanding of SNMP OID behavior and common monitoring pitfalls, often appearing as a trap where candidates mistakenly focus on polling frequency or manual checks. The key insight is that ifAdminStatus changes—like a script disabling and re-enabling the interface—will reset ifLastChange without reflecting a physical problem. A useful memory tip: think of ifLastChange as the “flap timestamp” that reveals whether the interface was intentionally toggled, not just broken.

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

✓

Monitor ifLastChange OID along with ifOperStatus to detect administrative flapping.

Option C is correct because ifLastChange provides the timestamp of the last state change. By cross-referencing ifLastChange with ifOperStatus, the monitoring system can detect that the 'down' event was administrative (ifAdminStatus changed) rather than a true link failure. Option A (using 'show interfaces extensive') is a manual command, not an automated monitoring solution. Option B (changing polling interval) does not distinguish between administrative and link failures. Option D (disabling the automated script) is a temporary workaround, not a robust monitoring improvement.

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.

✗
Use 'show interfaces extensive' to confirm interface status.
Why it's wrong here
Using 'show interfaces extensive' is a manual verification step, not an automated monitoring solution. It does not prevent false positives in the automated SNMP-based monitoring system.
✗
Change the SNMP polling interval to 1 minute.
Why it's wrong here
Changing the SNMP polling interval to 1 minute would increase the frequency of checks but still cannot distinguish between a true link failure and an administrative state change. It does not address the root cause.
✓
Monitor ifLastChange OID along with ifOperStatus to detect administrative flapping.
Why this is correct
Monitoring the ifLastChange OID along with ifOperStatus allows the monitoring system to detect the timestamp of the last state change. If the ifLastChange time matches the ifAdminStatus change time, the monitoring system can identify that the interface was administratively disabled/enabled, preventing a false positive alert.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable the automated script that caused the administrative disable.
Why it's wrong here
Disabling the automated script that caused the administrative disable is a temporary fix. It does not improve the monitoring system's ability to handle future administrative changes, which may occur from other sources.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Trap categories for this question

Command / output trap
Using 'show interfaces extensive' is a manual verification step, not an automated monitoring solution. It does not prevent false positives in the automated SNMP-based monitoring system.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 JNCIA-JUNOS exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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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: Monitor ifLastChange OID along with ifOperStatus to detect administrative flapping. — Option C is correct because ifLastChange provides the timestamp of the last state change. By cross-referencing ifLastChange with ifOperStatus, the monitoring system can detect that the 'down' event was administrative (ifAdminStatus changed) rather than a true link failure. Option A (using 'show interfaces extensive') is a manual command, not an automated monitoring solution. Option B (changing polling interval) does not distinguish between administrative and link failures. Option D (disabling the automated script) is a temporary workaround, not a robust monitoring improvement.

What should I do if I get this JNCIA-JUNOS question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks 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 JNCIA-JUNOS exam.