The answer is an unstable IGP route to 10.0.0.2, which causes the LDP neighbor flapping seen in the logs. LDP relies on IGP reachability to establish and maintain its neighbor sessions; when the underlying IGP route to the peer’s transport address becomes unstable—flapping between up and down—the LDP session follows suit, repeatedly transitioning between UP and DOWN states. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of LDP dependency on the IGP, often appearing in troubleshooting questions where repeated %LDP-5-NBRCHG messages point to route instability rather than a direct LDP misconfiguration. A common trap is to immediately blame LDP hello or hold timers, but the root cause is almost always a flapping IGP route or a mismatched LDP router ID. Remember the memory tip: “LDP flaps when the IGP takes a nap”—if the IGP route is unstable, LDP will follow.
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 R8:
R8# show logging | include %LDP-5-NBRCHG
*Mar 1 00:01:10.123: %LDP-5-NBRCHG: LDP Neighbor 10.0.0.2:0 (1) is UP
*Mar 1 00:02:20.456: %LDP-5-NBRCHG: LDP Neighbor 10.0.0.2:0 (1) is DOWN
*Mar 1 00:03:30.789: %LDP-5-NBRCHG: LDP Neighbor 10.0.0.2:0 (1) is UP
*Mar 1 00:04:40.012: %LDP-5-NBRCHG: LDP Neighbor 10.0.0.2:0 (1) 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 LDP session is flapping due to an unstable IGP route to 10.0.0.2.
The output shows LDP neighbor 10.0.0.2 flapping between UP and DOWN. This indicates instability in the LDP session, often due to a flapping IGP route (since LDP depends on IGP reachability), or a misconfiguration of LDP parameters such as hello interval or hold time.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 LDP session is flapping due to an unstable IGP route to 10.0.0.2.
Why this is correct
LDP relies on IGP to establish and maintain neighbors; if the IGP route is flapping, LDP will also flap.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Label exhaustion would cause label allocation failures, not neighbor flapping.
✗
The router has a mismatched LDP router ID.
Why it's wrong here
A mismatched router ID would prevent the neighbor from coming up at all, not cause flapping.
✗
The LDP hello interval is set too high, causing slow detection.
Why it's wrong here
A high hello interval would make the session slower to detect changes, but not cause flapping.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Network Logging and Syslog — This question tests Network Logging and Syslog — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The LDP session is flapping due to an unstable IGP route to 10.0.0.2. — The output shows LDP neighbor 10.0.0.2 flapping between UP and DOWN. This indicates instability in the LDP session, often due to a flapping IGP route (since LDP depends on IGP reachability), or a misconfiguration of LDP parameters such as hello interval or hold time.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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?
OSPF neighbours must agree on key parameters.
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