- A
LDP session is established and stable.
Why wrong: The hold timer expires, indicating instability.
- B
LDP session is flapping due to hold timer expiration.
The hold timer expires, causing the session to close, which suggests flapping.
- C
LDP session is down because of authentication failure.
Why wrong: No authentication error is shown.
- D
LDP session is down because of a transport address mismatch.
Why wrong: The transport connection is established, so addresses match.
Question 1,387 of 2,152
MPLS LDP Hold Timer Expiration Troubleshooting
This 300-410 practice question tests your understanding of device management. 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.
A network engineer runs the following command to troubleshoot an MPLS LDP issue:
R1# debug mpls ldp transport
LDP: Transport connection to 2.2.2.2:0 via TCP (passive) LDP: Connection from 2.2.2.2:0 to 1.1.1.1:646 LDP: Transport connection to 2.2.2.2:0 via TCP (active) LDP: Connection from 1.1.1.1:646 to 2.2.2.2:0 LDP: Hold timer expired for peer 2.2.2.2:0 LDP: Closing transport connection to 2.2.2.2:0
What does this output indicate?
Quick Answer
The answer is that the LDP session is flapping due to hold timer expiration. This is correct because the debug output shows the transport connection to peer 2.2.2.2 being established via TCP, but then the hold timer expires, forcing the session to close and immediately attempt reconnection. In MPLS LDP, the hold timer dictates how long a router waits for a keepalive message from its peer; if no keepalive is received within that interval, the session is torn down to prevent stale label bindings. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to differentiate between a session that never forms and one that flaps due to intermittent keepalive loss—a common trap is confusing hold timer expiration with a failed TCP transport. Remember the memory tip: "Hold timer hits zero, session goes hero" (meaning it resets and tries again), so always check for network congestion or mismatched hello/hold timers when you see this pattern.
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
✓
LDP session is flapping due to hold timer expiration.
The output shows the LDP hold timer expiring for peer 2.2.2.2, followed by the transport connection being closed. This indicates the LDP session is repeatedly going up and down (flapping) because the hold timer expires before the session can stabilize, often due to network congestion, high CPU, or mismatched hello/hold timers. Option B correctly identifies this flapping behavior caused by hold timer expiration.
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.
- ✗
LDP session is established and stable.
Why it's wrong here
The hold timer expires, indicating instability.
- ✓
LDP session is flapping due to hold timer expiration.
Why this is correct
The hold timer expires, causing the session to close, which suggests flapping.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
LDP session is down because of authentication failure.
Why it's wrong here
No authentication error is shown.
- ✗
LDP session is down because of a transport address mismatch.
Why it's wrong here
The transport connection is established, so addresses match.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between session flapping due to hold timer expiration versus session failure due to authentication or address mismatch, and the trap here is that candidates may see 'transport connection' messages and incorrectly assume the session is up, missing the critical 'Hold timer expired' line.
Trap categories for this question
Command / output trap
No authentication error is shown.
Detailed technical explanation
How to think about this question
LDP uses a hold timer (default 180 seconds) to maintain the session; if no LDP PDUs (including keepalives) are received within that interval, the session is torn down. The debug output shows both passive and active transport connections, indicating the LDP discovery phase succeeded, but the session fails to maintain due to hold timer expiry—often caused by packet loss or delayed keepalives in congested networks. In real-world scenarios, this can occur when MPLS LDP is enabled over a link with high latency or when the router's control plane is overloaded.
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 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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: LDP session is flapping due to hold timer expiration. — The output shows the LDP hold timer expiring for peer 2.2.2.2, followed by the transport connection being closed. This indicates the LDP session is repeatedly going up and down (flapping) because the hold timer expires before the session can stabilize, often due to network congestion, high CPU, or mismatched hello/hold timers. Option B correctly identifies this flapping behavior caused by hold timer expiration.
What should I do if I get this 300-410 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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Last reviewed: Jul 4, 2026
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