The answer is to issue the 'clear lacp statistics' command on the interface to reset LACP negotiation. This is correct because the 'detached' state in LACP indicates that the physical link is operational, but the LACP state machine has failed to complete negotiation, often due to stale protocol information or a mismatch in PDU exchange after a fiber repair. The 'clear lacp statistics' command resets the LACP counters and forces the interface to re-initiate LACP PDUs, allowing it to renegotiate with the peer and rejoin the aggregated Ethernet bundle without impacting active traffic on other member links. On the JNCIA-Junos exam, this scenario tests your understanding of LACP states and recovery procedures, often appearing as a trap where candidates mistakenly check optical diagnostics or bounce the entire bundle. A common memory tip: think of LACP as a handshake that can get stuck—clearing statistics is like resetting the handshake without dropping the other hands already clasped.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
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 service provider has two MX routers (R1 and R2) connected via two separate physical links. Both links are in an aggregated Ethernet bundle (ae0). The ae0 interface is configured with LACP active on both sides. Recently, a fiber cut occurred on one of the member links, and the aggregated interface continued working. However, after the fiber was repaired, the network operator noticed that the restored link is not being re-added to the bundle. 'show lacp interfaces' indicates the link is in a 'detached' state. The operator checks 'show interfaces diagnostics optics' and finds that the optical parameters are normal. Which action should the operator take to restore the link to the bundle without affecting traffic?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Issue the 'clear lacp statistics' command on the interface to reset LACP negotiation on that link
Option C is correct because the 'detached' state in LACP indicates that the link is physically up but LACP negotiation has failed or is stuck. The 'clear lacp statistics' command resets the LACP state machine on the specified interface, forcing it to re-initiate LACP PDUs and renegotiate with the peer. This restores the link to the bundle without disrupting active traffic on other member links.
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.
✗
Reboot the router to clear all LACP states
Why it's wrong here
Rebooting is unnecessary and causes a full outage.
✗
Remove and re-add the member link from the ae0 configuration
Why it's wrong here
This could cause traffic disruption if the link is part of a load-balanced bundle, and requires a commit.
✓
Issue the 'clear lacp statistics' command on the interface to reset LACP negotiation on that link
Why this is correct
Clearing LACP statistics resets the LACP state machine, allowing the link to re-negotiate and join the bundle.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replace the SFP module on the restored link
Why it's wrong here
The optical diagnostics show normal parameters, so the SFP is likely not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a physical layer issue (like a bad SFP) or a configuration change is needed, when in fact the problem is a stuck LACP state machine that can be resolved with a non-disruptive clear command.
Trap categories for this question
Command / output trap
The optical diagnostics show normal parameters, so the SFP is likely not the issue.
Detailed technical explanation
How to think about this question
LACP uses a state machine defined in IEEE 802.3ad, where each link transitions through 'detached', 'waiting', 'attached', and 'collecting/distributing' states. A 'detached' state after a fiber repair often occurs because the LACP timeout expired during the outage and the link's actor/partner state machines are out of sync; 'clear lacp statistics' resets the per-interface LACP counters and state, forcing a fresh exchange of LACPDUs. In real-world scenarios, this command is the standard first step for recovering a link stuck in 'detached' without impacting other bundle members.
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: Issue the 'clear lacp statistics' command on the interface to reset LACP negotiation on that link — Option C is correct because the 'detached' state in LACP indicates that the link is physically up but LACP negotiation has failed or is stuck. The 'clear lacp statistics' command resets the LACP state machine on the specified interface, forcing it to re-initiate LACP PDUs and renegotiate with the peer. This restores the link to the bundle without disrupting active traffic on other member links.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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