The answer is that R1 has discovered two LDP neighbors via link hellos on two different interfaces. This is correct because the `show mpls ldp discovery detail` command reveals the discovery sources for the Label Distribution Protocol, specifically showing that each neighbor was learned through a directly connected interface rather than through targeted hellos. The output lists GigabitEthernet0/0 and GigabitEthernet0/1 as the discovery sources, each with a peer LDP Id and a hold time of 15 seconds, confirming basic link-level neighbor discovery. On the Cisco CCNP ENARSI 300-410 exam, this command tests your ability to differentiate between link and targeted LDP discovery, a common area where candidates confuse the two. A frequent trap is assuming that any LDP neighbor shown must be from a targeted session, but the presence of an interface name under "Discovery Sources" always indicates a link hello. Remember the memory tip: "If you see an interface, it’s a link hello; if you see a target address, it’s targeted."
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 discovery sources:
R1# show mpls ldp discovery detail
Output:
Local LDP Identifier: 10.0.0.1:0
Discovery Sources:
Interfaces:
GigabitEthernet0/0 (hello interval 5 s, targeted hello interval 10 s)
LDP Id: 10.0.0.2:0, transport address: 10.0.0.2
Hold time: 15 s (local: 15, peer: 15)
GigabitEthernet0/1 (hello interval 5 s, targeted hello interval 10 s)
LDP Id: 10.0.0.3:0, transport address: 10.0.0.3
Hold time: 15 s (local: 15, peer: 15)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
R1 has discovered two LDP neighbors via link hellos on two different interfaces
The output shows LDP discovery sources. R1 has discovered two LDP neighbors via link hellos on interfaces GigabitEthernet0/0 and GigabitEthernet0/1. Both neighbors have a hold time of 15 seconds.
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 has discovered two LDP neighbors via link hellos on two different interfaces
Why this is correct
The output shows two interfaces with LDP neighbors discovered via link hellos.
The discovery sources are interfaces, indicating link hellos, not targeted.
✗
R1 has no LDP neighbors
Why it's wrong here
Two neighbors are listed.
✗
The LDP session with 10.0.0.2 is down
Why it's wrong here
The neighbor is listed in discovery, so the session is likely up.
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 has discovered two LDP neighbors via link hellos on two different interfaces — The output shows LDP discovery sources. R1 has discovered two LDP neighbors via link hellos on interfaces GigabitEthernet0/0 and GigabitEthernet0/1. Both neighbors have a hold time of 15 seconds.
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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