The correct interpretation is that the LDP session with 10.0.0.2 failed due to malformed messages from the neighbor. When debugging LDP errors, the output specifically shows “malformed hello” and “malformed initialization” messages, which indicate that the received packets violate the LDP protocol format or contain unexpected parameters. This is a critical concept for the Cisco CCNP ENARSI 300-410 exam, where you must distinguish between session failures caused by authentication issues, transport problems, or malformed messages. A common trap is to assume the neighbor is unreachable, but the debug clearly shows the packets are received yet rejected due to corruption or misconfiguration—often pointing to a software bug or mismatched LDP parameters on the remote router. For the exam, remember that “malformed” always points to the content of the message itself, not the connectivity. A helpful memory tip: “Malformed means the message is formed wrong, not the neighbor gone.”
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 debug MPLS LDP errors:
R1# debug mpls ldp errors
Output:
*Mar 1 00:01:23.456: LDP: Received malformed hello from 10.0.0.2
*Mar 1 00:01:23.789: LDP: Received malformed initialization from 10.0.0.2
*Mar 1 00:01:24.012: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN
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 with 10.0.0.2 failed due to malformed messages from the neighbor
The debug output shows LDP errors. R1 received malformed hello and initialization messages from neighbor 10.0.0.2, causing the LDP session to go down. This indicates a configuration mismatch or software bug on the neighbor.
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 with 10.0.0.2 failed due to malformed messages from the neighbor
Why this is correct
Malformed messages were received, leading to session teardown.
The errors indicate received malformed messages, not sent.
✗
The LDP session is using incorrect transport address
Why it's wrong here
The error is about malformed messages, not transport address.
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.
MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The LDP session with 10.0.0.2 failed due to malformed messages from the neighbor — The debug output shows LDP errors. R1 received malformed hello and initialization messages from neighbor 10.0.0.2, causing the LDP session to go down. This indicates a configuration mismatch or software bug on the neighbor.
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.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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