The answer is that R1 will pop the label for 10.0.0.0/8 before forwarding to the next hop. This is correct because the local binding shows "imp-null," which is label 3, also known as implicit null. When an LSR assigns implicit null to a prefix, it instructs the upstream router to pop the MPLS label before sending the packet, effectively performing Penultimate Hop Popping (PHP). In this output, R1 is the penultimate hop for 10.0.0.0/8, so it will remove the label and forward the IP packet to the egress LSR. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of MPLS label operations and the difference between implicit null (label 3) and explicit null (label 0). A common trap is confusing "imp-null" with a missing label—remember that imp-null is an active instruction to pop, not an absence of a label. Memory tip: "Implicit Null = I'm Popping, Hop!"
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. 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 LDP label bindings for a specific prefix:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
R1 will pop the label for 10.0.0.0/8 before forwarding to the next hop
The output shows label bindings for prefix 10.0.0.0/8. R1 has assigned implicit null label (label 3) locally, meaning it will pop the label before forwarding. Neighbor 10.0.0.2 also uses implicit null, while 10.0.0.3 uses label 302.
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.
✓
R1 will pop the label for 10.0.0.0/8 before forwarding to the next hop
Why this is correct
Implicit null (imp-null) means the router will pop the label (PHP - Penultimate Hop Popping).
All neighbors are using implicit null for this prefix
Why it's wrong here
Neighbor 10.0.0.3 is using label 302, not implicit null.
✗
The prefix 10.0.0.0/8 is not in the routing table
Why it's wrong here
The presence of label bindings suggests the prefix is in the routing table.
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: R1 will pop the label for 10.0.0.0/8 before forwarding to the next hop — The output shows label bindings for prefix 10.0.0.0/8. R1 has assigned implicit null label (label 3) locally, meaning it will pop the label before forwarding. Neighbor 10.0.0.2 also uses implicit null, while 10.0.0.3 uses label 302.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer runs the following command to verify MPLS LDP label bindings:
R1# show mpls ldp bindings 192.168.1.0 255.255.255.0
Output:
lib entry: 192.168.1.0/24, rev 8
local binding: label: 101
remote binding: lsr: 10.0.0.2:0, label: 201
remote binding: lsr: 10.0.0.3:0, label: 301
What does this output indicate?
medium
✓ A.The prefix 192.168.1.0/24 has a local label of 101 and two remote labels from LDP neighbors
B.The prefix 192.168.1.0/24 is not reachable via any LDP neighbor
C.Label 101 is the only label assigned to this prefix in the network
D.The LDP session with 10.0.0.2 is down
Why A: The output shows the label bindings for the prefix 192.168.1.0/24 in the Label Information Base (LIB). The local label is 101, and two remote labels (201 from 10.0.0.2, 301 from 10.0.0.3) have been received from LDP neighbors.
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Question Discussion
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