- A
BFD is enabled for OSPF on this interface and will detect failures faster than OSPF's hello/dead timers.
Why wrong: Incorrect because OSPF must be configured to use BFD with 'bfd all-interfaces' or 'bfd interface' under the OSPF process.
- B
BFD is configured on the interface but will not be used by OSPF unless the 'bfd all-interfaces' command is added under router ospf.
Correct. BFD interface configuration alone does not enable BFD for OSPF; the routing protocol must be told to use it.
- C
BFD will only be used if the neighbor also has BFD configured with the same timer values.
Why wrong: While BFD requires both sides to have BFD configured, the primary issue here is that OSPF is not enabled to use BFD.
- D
The BFD configuration is invalid because the interval and min_rx values must be identical on both sides.
Why wrong: BFD timers are negotiated; they do not need to be identical. The router proposes its values and the neighbor may accept or adjust.
Quick Answer
The answer is that BFD will not be used by OSPF unless the `bfd all-interfaces` command is added under the OSPF routing process. This is because BFD configuration on an interface, such as setting the `bfd interval` and timers, only enables the BFD session at the link level; OSPF requires an explicit directive to integrate that session for neighbor failure detection. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that BFD is a two-step configuration—interface-level parameters and protocol-level activation—and a common trap is assuming the interface commands alone are sufficient. Remember that OSPF will ignore BFD until you issue `bfd all-interfaces` or `bfd` under the specific neighbor. A useful memory tip: "Interface enables the engine, OSPF turns on the ignition."
300-410 Bidirectional Forwarding Detection (BFD) Practice Question
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Consider the following partial configuration on a router:
interface GigabitEthernet0/1 ip address 10.1.1.1 255.255.255.252
bfd interval 100 min_rx 100 multiplier 3 !
router ospf 1 network 10.1.1.0 0.0.0.3 area 0
!
What is the effect of this configuration?
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
BFD is configured on the interface but will not be used by OSPF unless the 'bfd all-interfaces' command is added under router ospf.
The BFD configuration is applied under the interface, but OSPF must be explicitly configured to use BFD via the 'bfd all-interfaces' command under the OSPF routing process. Without this, BFD will not be used for OSPF neighbor failure detection.
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.
- ✗
BFD is enabled for OSPF on this interface and will detect failures faster than OSPF's hello/dead timers.
Why it's wrong here
Incorrect because OSPF must be configured to use BFD with 'bfd all-interfaces' or 'bfd interface' under the OSPF process.
- ✓
BFD is configured on the interface but will not be used by OSPF unless the 'bfd all-interfaces' command is added under router ospf.
- ✗
BFD will only be used if the neighbor also has BFD configured with the same timer values.
Why it's wrong here
While BFD requires both sides to have BFD configured, the primary issue here is that OSPF is not enabled to use BFD.
- ✗
The BFD configuration is invalid because the interval and min_rx values must be identical on both sides.
Why it's wrong here
BFD timers are negotiated; they do not need to be identical. The router proposes its values and the neighbor may accept or adjust.
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.
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?
Bidirectional Forwarding Detection (BFD) — This question tests Bidirectional Forwarding Detection (BFD) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: BFD is configured on the interface but will not be used by OSPF unless the 'bfd all-interfaces' command is added under router ospf. — The BFD configuration is applied under the interface, but OSPF must be explicitly configured to use BFD via the 'bfd all-interfaces' command under the OSPF routing process. Without this, BFD will not be used for OSPF neighbor failure detection.
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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