Quick Answer
The answer is that BFD is enabled for LDP, allowing faster LDP session failure detection. This is correct because the output from the show mpls ldp neighbor detail command explicitly includes the line “BFD enabled, BFD state: UP,” confirming that Bidirectional Forwarding Detection is actively monitoring the MPLS LDP session between 10.6.6.1 and 10.6.6.2. BFD provides sub-second failure detection, which is far quicker than the default LDP hello hold timer, enabling rapid convergence in MPLS networks. On the Cisco CCNP ENARSI 300-410 exam, this verification scenario tests your ability to interpret LDP neighbor details and understand how BFD integrates with LDP to improve network resilience. A common trap is confusing the BFD state with the LDP session state—here, the LDP session is “Oper” (operational), but the BFD state being “UP” is the key indicator that fast failure detection is active. Memory tip: “BFD UP means fast drop—LDP won’t wait for the hello clock to stop.”
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). 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 BFD with MPLS LDP:
R1# show mpls ldp neighbor 10.6.6.2 detail
Peer LDP Ident: 10.6.6.2:0, Local LDP Ident: 10.6.6.1:0 TCP connection: 10.6.6.2.646 - 10.6.6.1.53456 State: Oper; Msgs sent/rcvd: 100/100; Downstream Up time: 00:10:00 LDP discovery sources: GigabitEthernet0/2, hello interval: 5 s, hello hold: 15 s Addresses bound to peer LDP ident:
10.6.6.2 10.7.7.2
BFD enabled, BFD state: UP
What does this output indicate?
BFD is enabled for LDP, allowing faster LDP session failure detection.
BFD is enabled and UP, enabling sub-second detection for LDP.
BFD is disabled for this LDP session.
Why wrong: The output clearly states 'BFD enabled'.
LDP is using BFD only for IPv6.
Why wrong: No IPv6 is mentioned; this is an IPv4 LDP session.
BFD state is DOWN, so LDP uses its own hello timers.
Why wrong: BFD state is UP.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
BFD is enabled for LDP, allowing faster LDP session failure detection.
The output shows that BFD is enabled for the LDP session and the BFD state is UP, providing fast failure detection for MPLS LDP neighbor.
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.
BFD is enabled for LDP, allowing faster LDP session failure detection.
Why this is correct
BFD is enabled and UP, enabling sub-second detection for LDP.
Related concept
OSPF neighbours must agree on key parameters.
BFD is disabled for this LDP session.
Why it's wrong here
The output clearly states 'BFD enabled'.
LDP is using BFD only for IPv6.
Why it's wrong here
No IPv6 is mentioned; this is an IPv4 LDP session.
BFD state is DOWN, so LDP uses its own hello timers.
Why it's wrong here
BFD state is UP.
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
The output clearly states 'BFD enabled'.
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 300-410 OSPF questions on adjacency and route selection.
Bidirectional Forwarding Detection (BFD) — study guide chapter
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FAQ
Bidirectional Forwarding Detection (BFD) — This question tests Bidirectional Forwarding Detection (BFD) — OSPF neighbours must agree on key parameters..
The correct answer is: BFD is enabled for LDP, allowing faster LDP session failure detection. — The output shows that BFD is enabled for the LDP session and the BFD state is UP, providing fast failure detection for MPLS LDP neighbor.
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.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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