- A
The output of 'show mpls forwarding-table' shows 'no label' for a specific prefix.
This indicates that the router has not received a label binding for that prefix from its LDP neighbor, causing packets to be forwarded without MPLS.
- B
The output of 'show mpls ldp neighbor' shows 'state: OPERATIONAL' for all neighbors.
Why wrong: This is a normal, healthy state for LDP neighbors, not a symptom of an issue.
- C
The output of 'debug mpls ldp errors' shows 'Label bindings not received from peer'.
This indicates that the router is not receiving label bindings from an LDP peer, which can cause forwarding failures.
- D
The output of 'show mpls forwarding-table' shows 'Pop tag' for a prefix on a router that is not the egress LSR.
The 'Pop tag' operation should only appear on the penultimate hop router (PHP). If it appears on a non-egress router, it indicates a label distribution problem.
- E
The output of 'show mpls interfaces' shows 'IP' only for an interface configured for MPLS.
Why wrong: If an interface is configured for MPLS, 'show mpls interfaces' should show 'IP' and 'MPLS'. Showing only 'IP' means MPLS is not enabled, which is a configuration issue, but it is not a symptom of a label switching issue per se—it is a missing configuration.
Quick Answer
The correct answer is that a router showing 'Pop tag' in the output of 'show mpls forwarding-table' for a prefix when it is not the egress LSR is a key symptom of an MPLS label switching issue. This occurs because the Penultimate Hop Popping (PHP) operation should only be performed by the router directly upstream of the egress; if a non-egress router is popping the label, it indicates a misconfiguration in the label distribution or forwarding path, often due to an incorrect LDP session or a missing implicit-null label. On the Cisco CCNP ENARSI 300-410 exam, this question tests your ability to differentiate between normal MPLS operations and fault conditions, with common traps including mistaking 'show mpls ldp neighbor' showing 'OPERATIONAL' as a problem or overlooking that 'no label' in the forwarding table signals a missing binding. A reliable memory tip is "Pop only at the penultimate hop"—if you see 'Pop tag' anywhere else, suspect a label switching issue.
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. 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.
Which THREE symptoms indicate a potential MPLS label switching issue on a Cisco router? (Choose THREE.)
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
The output of 'show mpls forwarding-table' shows 'no label' for a specific prefix.
MPLS issues often manifest as incorrect label operations. 'show mpls forwarding-table' showing 'no label' for a route indicates a missing label binding. 'show mpls ldp neighbor' showing 'state: OPERATIONAL' is normal, not a symptom. 'debug mpls ldp errors' showing 'Label bindings not received' indicates a problem. 'show mpls forwarding-table' showing 'Pop tag' for a non-egress router suggests a misconfiguration. 'show mpls interfaces' showing 'IP' only (not MPLS) indicates MPLS is not enabled on the interface.
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 output of 'show mpls forwarding-table' shows 'no label' for a specific prefix.
Why this is correct
This indicates that the router has not received a label binding for that prefix from its LDP neighbor, causing packets to be forwarded without MPLS.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The output of 'show mpls ldp neighbor' shows 'state: OPERATIONAL' for all neighbors.
Why it's wrong here
This is a normal, healthy state for LDP neighbors, not a symptom of an issue.
- ✓
The output of 'debug mpls ldp errors' shows 'Label bindings not received from peer'.
Why this is correct
This indicates that the router is not receiving label bindings from an LDP peer, which can cause forwarding failures.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
The output of 'show mpls forwarding-table' shows 'Pop tag' for a prefix on a router that is not the egress LSR.
Why this is correct
The 'Pop tag' operation should only appear on the penultimate hop router (PHP). If it appears on a non-egress router, it indicates a label distribution problem.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The output of 'show mpls interfaces' shows 'IP' only for an interface configured for MPLS.
Why it's wrong here
If an interface is configured for MPLS, 'show mpls interfaces' should show 'IP' and 'MPLS'. Showing only 'IP' means MPLS is not enabled, which is a configuration issue, but it is not a symptom of a label switching issue per se—it is a missing configuration.
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
If an interface is configured for MPLS, 'show mpls interfaces' should show 'IP' and 'MPLS'. Showing only 'IP' means MPLS is not enabled, which is a configuration issue, but it is not a symptom of a label switching issue per se—it is a missing configuration.
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.
What to study next
Got this wrong? Here's your next step.
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.
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FAQ
Questions learners often ask
What does this 300-410 question test?
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 output of 'show mpls forwarding-table' shows 'no label' for a specific prefix. — MPLS issues often manifest as incorrect label operations. 'show mpls forwarding-table' showing 'no label' for a route indicates a missing label binding. 'show mpls ldp neighbor' showing 'state: OPERATIONAL' is normal, not a symptom. 'debug mpls ldp errors' showing 'Label bindings not received' indicates a problem. 'show mpls forwarding-table' showing 'Pop tag' for a non-egress router suggests a misconfiguration. 'show mpls interfaces' showing 'IP' only (not MPLS) indicates MPLS is not enabled on the interface.
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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Last reviewed: Jun 18, 2026
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