The answer is that the router has learned labels for three prefixes from LSR 10.0.0.2. This is correct because the show mpls ldp bindings command displays the Label Information Base (LIB), where each “lib entry” lists a prefix, the local label assigned by the local router, and the remote label learned from a specific LSR. In the output, all three remote bindings originate from LSR 10.0.0.2, confirming label distribution for those prefixes. On the Cisco CCNP ENARSI 300-410 exam, this command tests your understanding of MPLS LDP operation and the distinction between local and remote bindings. A common trap is misinterpreting “imp-null” as a missing label; in reality, it indicates implicit null (label 3), used for Penultimate Hop Popping (PHP) in a BGP-free core. Memory tip: “Local is mine, remote is theirs—imp-null means pop before it shares.”
300-410 MPLS L3VPN Practice Question
This 300-410 practice question tests your understanding of mpls l3vpn. 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 to verify MPLS L3VPN operation:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router has learned labels for three prefixes from LSR 10.0.0.2
The show mpls ldp bindings command displays the Label Information Base (LIB) entries. Each entry shows a prefix, the local label assigned by this router, and the remote label learned from a specific LSR (10.0.0.2). The third entry shows 'imp-null' for the remote label, meaning the neighbor is using implicit null (label 3) for that prefix, typically for BGP-free core or PHP.
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 router has learned labels for three prefixes from LSR 10.0.0.2
Why this is correct
The output shows three LIB entries with remote bindings from 10.0.0.2.
This output does not indicate BGP route reflection.
✗
The router has a label for 10.3.3.0/24 that is implicit null
Why it's wrong here
The local label is 103; the remote label from 10.0.0.2 is imp-null, not the local label.
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.
Trap categories for this question
Command / output trap
No TE-related information is shown.
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 L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The router has learned labels for three prefixes from LSR 10.0.0.2 — The show mpls ldp bindings command displays the Label Information Base (LIB) entries. Each entry shows a prefix, the local label assigned by this router, and the remote label learned from a specific LSR (10.0.0.2). The third entry shows 'imp-null' for the remote label, meaning the neighbor is using implicit null (label 3) for that prefix, typically for BGP-free core or PHP.
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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