- A
The distribute-list is applied outbound, but OSPF distribute-lists only filter routes in the routing table, not LSAs, so the routes are still advertised.
Correct. OSPF distribute-lists outbound do not filter LSAs; they only filter routes from being installed in the routing table. The neighbor will still receive the LSA.
- B
The BFD session is flapping due to a mismatch in the 'bfd interval' command, causing OSPF to withdraw routes.
Why wrong: Incorrect. BFD flapping would cause OSPF to remove routes, but the distribute-list is the configured filter.
- C
The distribute-list references an ACL that denies the network, but OSPF uses type 3 LSAs that are not affected by ACLs.
Why wrong: Incorrect. OSPF distribute-lists can use ACLs, but they still only affect route installation, not LSA flooding.
- D
The 'area range' command is configured on the ABR, summarizing the route, and the distribute-list is filtering the summary.
Why wrong: Incorrect. The 'area range' command creates a summary LSA, which is still an LSA and not filtered by distribute-lists.
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.
An engineer configures BFD on an OSPF link and also applies a distribute-list outbound under the OSPF process. The BFD session is up, but OSPF routes are not being advertised to the neighbor. The engineer verifies that the distribute-list is correctly configured. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The distribute-list is applied outbound, but OSPF distribute-lists only filter routes in the routing table, not LSAs, so the routes are still advertised.
OSPF distribute-lists only filter routes in the routing table, not LSAs. If the distribute-list is filtering the route, OSPF will still advertise the LSA to the neighbor, but the neighbor will not install the route. However, if the distribute-list is applied inbound, it can prevent the route from being installed. The edge case here is that the distribute-list is applied outbound, which has no effect on OSPF LSA flooding. BFD does not interact with distribute-lists.
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.
- ✓
The distribute-list is applied outbound, but OSPF distribute-lists only filter routes in the routing table, not LSAs, so the routes are still advertised.
Why this is correct
Correct. OSPF distribute-lists outbound do not filter LSAs; they only filter routes from being installed in the routing table. The neighbor will still receive the LSA.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The BFD session is flapping due to a mismatch in the 'bfd interval' command, causing OSPF to withdraw routes.
Why it's wrong here
Incorrect. BFD flapping would cause OSPF to remove routes, but the distribute-list is the configured filter.
- ✗
The distribute-list references an ACL that denies the network, but OSPF uses type 3 LSAs that are not affected by ACLs.
- ✗
The 'area range' command is configured on the ABR, summarizing the route, and the distribute-list is filtering the summary.
Why it's wrong here
Incorrect. The 'area range' command creates a summary LSA, which is still an LSA and not filtered by distribute-lists.
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
Incorrect. The 'area range' command creates a summary LSA, which is still an LSA and not filtered by distribute-lists.
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: The distribute-list is applied outbound, but OSPF distribute-lists only filter routes in the routing table, not LSAs, so the routes are still advertised. — OSPF distribute-lists only filter routes in the routing table, not LSAs. If the distribute-list is filtering the route, OSPF will still advertise the LSA to the neighbor, but the neighbor will not install the route. However, if the distribute-list is applied inbound, it can prevent the route from being installed. The edge case here is that the distribute-list is applied outbound, which has no effect on OSPF LSA flooding. BFD does not interact with distribute-lists.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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