The answer is that BFD multihop sessions require explicit configuration of source and destination IP addresses, use UDP port 4784, and operate over multiple routed hops. This is correct because unlike single-hop BFD, which runs on directly connected neighbors using UDP port 3784 and automatically derives peer addresses, multihop BFD is designed for non-adjacent routers and must have both endpoints manually specified to establish the session. On the Cisco CCNP ENARSI 300-410 exam, this topic tests your understanding of BFD deployment scenarios, often appearing in a multiple-choice question where common traps include assuming multihop sessions require the same subnet or that they use the same port as single-hop sessions. A key memory tip is to associate the number 4 with multihop: port 4784 for multiple hops, while single-hop uses 3784.
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.
Which THREE statements about BFD multihop sessions are true? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Multihop BFD is used when the neighbors are not directly connected.
BFD multihop sessions are used when the two routers are not directly connected, requiring multiple hops. They use a different destination UDP port (4784) compared to single-hop sessions (3784). Additionally, multihop sessions require explicit configuration of the BFD source and destination IP addresses. The other statements are false because multihop sessions do not require the same subnet, and they can operate over any routed path.
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.
✓
Multihop BFD is used when the neighbors are not directly connected.
Why this is correct
Multihop BFD supports sessions between routers separated by multiple Layer 3 hops.
Multihop BFD requires both routers to be in the same subnet.
Why it's wrong here
Multihop sessions can span different subnets; they are not limited to directly connected subnets.
✗
Multihop BFD can only be used with BGP.
Why it's wrong here
Multihop BFD can be used with various routing protocols, including OSPF, EIGRP, and static routes.
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.
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: Multihop BFD is used when the neighbors are not directly connected. — BFD multihop sessions are used when the two routers are not directly connected, requiring multiple hops. They use a different destination UDP port (4784) compared to single-hop sessions (3784). Additionally, multihop sessions require explicit configuration of the BFD source and destination IP addresses. The other statements are false because multihop sessions do not require the same subnet, and they can operate over any routed path.
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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Question Discussion
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