The answer is 250 ms, calculated as the multiplier of 5 multiplied by the negotiated timer of 50 ms. This is correct because BFD failure detection time is computed by taking the negotiated interval—which is the greater of the configured *bfd interval* and *min_rx* values—and multiplying it by the multiplier; here both values are 50 ms, so the detection time is 5 × 50 ms = 250 ms. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how BFD timers are negotiated and applied, often appearing in questions that mix interface-level and routing-protocol-level BFD commands. A common trap is forgetting that the multiplier applies to the *maximum* of the two timer values, not just the transmit interval. Remember the formula: Detection Time = Multiplier × max(interval, min_rx).
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.
Examine the following configuration:
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
bfd interval 50 min_rx 50 multiplier 5
!
router eigrp TEST
network 192.168.1.0
bfd interface GigabitEthernet0/0
!
Which statement is true about BFD operation on this interface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
BFD will detect a failure in 250 ms (5 x 50 ms).
The 'bfd interface' command under EIGRP enables BFD for that specific interface. The BFD session will negotiate timers; the multiplier of 5 means the session will declare a neighbor down after 5 * max(min_rx, negotiated interval) = 5 * 50 = 250 ms of missed packets.
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 will detect a failure in 250 ms (5 x 50 ms).
Why this is correct
Correct. The detection time is multiplier * the negotiated interval, which in this case is 5 * 50 ms = 250 ms.
BFD will detect a failure in 50 ms because the interval is set to 50 ms.
Why it's wrong here
The detection time is multiplier * interval, not just the interval itself.
✗
BFD is enabled but only for EIGRP; it will not affect any other routing protocol.
Why it's wrong here
While this is true, it does not address the detection time calculation.
✗
The configuration is missing 'bfd all-interfaces' under EIGRP, so BFD will not work.
Why it's wrong here
The 'bfd interface' command is sufficient to enable BFD on a specific interface; 'bfd all-interfaces' is an alternative.
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
The 'bfd interface' command is sufficient to enable BFD on a specific interface; 'bfd all-interfaces' is an alternative.
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.
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 will detect a failure in 250 ms (5 x 50 ms). — The 'bfd interface' command under EIGRP enables BFD for that specific interface. The BFD session will negotiate timers; the multiplier of 5 means the session will declare a neighbor down after 5 * max(min_rx, negotiated interval) = 5 * 50 = 250 ms of missed packets.
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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