The answer is an unstable IPsec SA causing DMVPN NHRP peer flapping. This is correct because the repeated UP/DOWN transitions of peer 10.0.0.1 on Tunnel0, as shown in the logging output, directly indicate that the underlying IPsec security association is failing and being renegotiated, which in turn destabilizes the NHRP adjacency. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to differentiate between NHRP-specific issues and IPsec-related instability; a common trap is to immediately blame NHRP hold-time or routing problems, but the rapid, cyclical pattern of adjacency changes points squarely to IPsec SA expiration or misconfiguration. Remember that DMVPN relies on mGRE and NHRP, but the tunnel’s stability ultimately depends on a healthy IPsec SA—if the SA drops, NHRP follows. Memory tip: “SA down, NHRP frown” — when the IPsec SA flaps, the NHRP peer will flap right along with it.
300-410 Network Logging and Syslog Practice Question
This 300-410 practice question tests your understanding of network logging and syslog. 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 network engineer runs the following command on Router R9:
R9# show logging | include %DMVPN-5-ADJCHG
*Mar 1 00:01:05.123: %DMVPN-5-ADJCHG: NHRP: Peer 10.0.0.1 on Tunnel0 is UP
*Mar 1 00:02:10.456: %DMVPN-5-ADJCHG: NHRP: Peer 10.0.0.1 on Tunnel0 is DOWN
*Mar 1 00:03:15.789: %DMVPN-5-ADJCHG: NHRP: Peer 10.0.0.1 on Tunnel0 is UP
*Mar 1 00:04:20.012: %DMVPN-5-ADJCHG: NHRP: Peer 10.0.0.1 on Tunnel0 is DOWN
Based on this output, what is the most likely problem?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DMVPN tunnel is flapping due to an unstable IPsec SA.
The output shows NHRP peer flapping on Tunnel0, indicating that the DMVPN tunnel is unstable. This is often due to a flaking physical interface, IPsec SA expiration, or routing issues. The peer 10.0.0.1 is going up and down repeatedly.
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.
✓
The DMVPN tunnel is flapping due to an unstable IPsec SA.
Why this is correct
DMVPN uses IPsec for encryption; if the IPsec SA is not established or is flapping, the NHRP peer will go up and down.
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 NHRP hold time is set too high.
Why it's wrong here
A high hold time would make the peer take longer to go down, but the pattern shows quick flapping.
✗
The router has a mismatched DMVPN phase configuration.
Why it's wrong here
Mismatched phases would prevent the peer from coming up at all.
✗
The tunnel interface is administratively down.
Why it's wrong here
If the tunnel were administratively down, no peers would come up.
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
A high hold time would make the peer take longer to go down, but the pattern shows quick flapping.
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 300-410 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 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.
Network Logging and Syslog — This question tests Network Logging and Syslog — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The DMVPN tunnel is flapping due to an unstable IPsec SA. — The output shows NHRP peer flapping on Tunnel0, indicating that the DMVPN tunnel is unstable. This is often due to a flaking physical interface, IPsec SA expiration, or routing issues. The peer 10.0.0.1 is going up and down repeatedly.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 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.
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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