Quick Answer
The answer is the **show mpls forwarding-table** command, which must be checked on the P routers to verify the LSP path when the ingress PE has the label binding but no LSP is established. This command displays the actual label forwarding entries (the LFIB) on each intermediate router, allowing you to trace the label-switched path hop-by-hop and identify missing or incorrect label assignments that break the LSP. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this question tests your ability to isolate MPLS forwarding failures rather than control-plane issues—a common trap is to check LDP neighbors (show mpls ldp neighbor) or MPLS interfaces (show mpls interfaces), but those only verify peering and interface status, not the actual data-plane forwarding entries. Remember: the forwarding-table is the data-plane truth; if the label swap or pop is missing there, the LSP is broken regardless of LDP state. Memory tip: **F**orwarding-table = **F**ind the **F**ailure—it shows you exactly where the packet stops being label-switched.
This 350-501 practice question tests your understanding of networking. 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.
An engineer is troubleshooting MPLS LSP connectivity. The ingress PE router has the label binding for the FEC 10.1.1.0/24, but no LSP is established. Which command should be checked on the P routers to verify the LSP path?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
show mpls interface
Why wrong: Shows interfaces enabled for MPLS, not forwarding entries.
show mpls ldp neighbor
Why wrong: Shows LDP neighbors, not forwarding details.
show mpls forwarding-table
Displays MPLS forwarding entries, revealing label path issues.
show ip route 10.1.1.0
Why wrong: Shows IP routing table, not MPLS forwarding.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
show mpls forwarding-table
Option B is correct because 'show mpls forwarding-table' displays the label forwarding entries and can identify missing or incorrect label assignments along the path. Option A is not specific to MPLS forwarding; option C shows LDP neighbors only; option D shows MPLS interfaces but not forwarding details.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
show mpls interface
Why it's wrong here
Shows interfaces enabled for MPLS, not forwarding entries.
show mpls ldp neighbor
Why it's wrong here
Shows LDP neighbors, not forwarding details.
show mpls forwarding-table
Why this is correct
Displays MPLS forwarding entries, revealing label path issues.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
show ip route 10.1.1.0
Why it's wrong here
Shows IP routing table, not MPLS forwarding.
Common exam traps
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
Shows interfaces enabled for MPLS, not forwarding entries.
Detailed technical explanation
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.
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
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
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 350-501 OSPF questions on adjacency and route selection.
Networking — study guide chapter
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Networking practice questions
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Cisco SPCOR / CCNP Service Provider Core 350-501 study guide
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FAQ
Networking — This question tests Networking — OSPF neighbours must agree on key parameters..
The correct answer is: show mpls forwarding-table — Option B is correct because 'show mpls forwarding-table' displays the label forwarding entries and can identify missing or incorrect label assignments along the path. Option A is not specific to MPLS forwarding; option C shows LDP neighbors only; option D shows MPLS interfaces but not forwarding details.
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 350-501 OSPF questions on adjacency and route selection.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 24, 2026
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