The answer is a hold timer expiry due to delayed keepalives. This is correct because in Junos, the BGP hold timer defaults to 90 seconds, and if the router fails to receive a keepalive or update message within that interval, it assumes the peer is unreachable, resets the session, and transitions the BGP state to Idle or Active. On the JNCIA-Junos exam, this concept tests your understanding of BGP session maintenance and the role of keepalive intervals; a common trap is confusing a hold timer expiry with a TCP reset or configuration mismatch. Remember that the hold timer is three times the keepalive interval by default, so if keepalives are delayed or dropped, the hold timer will expire first. A useful memory tip: “Hold your breath for 90 seconds, but if no keepalive comes, the session is done.”
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
```
user@router> show log messages | match "BGP"
Jan 15 10:23:45 router rpd[1234]: BGP peer 10.0.1.2 (Internal) closed: Hold time expired
Jan 15 10:23:45 router rpd[1234]: BGP peer 10.0.1.2 (Internal) state changed from Established to Idle
```
Refer to the exhibit. What is the most likely cause of the BGP session failure?
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.
```
user@router> show log messages | match "BGP"
Jan 15 10:23:45 router rpd[1234]: BGP peer 10.0.1.2 (Internal) closed: Hold time expired
Jan 15 10:23:45 router rpd[1234]: BGP peer 10.0.1.2 (Internal) state changed from Established to Idle
```
A
Hold timer expired due to delayed keepalives
The log clearly states 'Hold time expired'.
B
The peer is unreachable
Why wrong: Could cause hold time expiry, but the direct reason is hold time expired.
C
BGP configuration mismatch
Why wrong: Not indicated in the log.
D
Route flapping
Why wrong: Does not directly cause hold time expiration.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Hold timer expired due to delayed keepalives
The BGP session failure is most likely due to the hold timer expiring because keepalive messages were not received in time. In JUNOS, the default hold time is 90 seconds, and if a router does not receive a keepalive or update within that interval, it declares the peer dead and resets the session. The exhibit shows the BGP state as 'Idle' or 'Active', which is consistent with a hold timer expiry event.
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.
✓
Hold timer expired due to delayed keepalives
Why this is correct
The log clearly states 'Hold time expired'.
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 peer is unreachable
Why it's wrong here
Could cause hold time expiry, but the direct reason is hold time expired.
✗
BGP configuration mismatch
Why it's wrong here
Not indicated in the log.
✗
Route flapping
Why it's wrong here
Does not directly cause hold time expiration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a BGP session failure is always due to a configuration mismatch or unreachable peer, but the hold timer expiry is a common operational issue caused by delayed keepalives, which is a key concept in BGP session maintenance.
Detailed technical explanation
How to think about this question
The BGP hold timer is negotiated during the OPEN message exchange, with each peer proposing a hold time and the lower value being used. If keepalives are delayed due to network congestion, high CPU load, or a slow peer, the hold timer can expire even if the peer is technically reachable. In JUNOS, you can verify hold timer expiry by checking the 'show bgp summary' output for the 'Holdtime' field and using 'monitor traffic' to inspect keepalive intervals.
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: Hold timer expired due to delayed keepalives — The BGP session failure is most likely due to the hold timer expiring because keepalive messages were not received in time. In JUNOS, the default hold time is 90 seconds, and if a router does not receive a keepalive or update within that interval, it declares the peer dead and resets the session. The exhibit shows the BGP state as 'Idle' or 'Active', which is consistent with a hold timer expiry event.
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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