The answer is that the redistribute ospf 1 command under OSPF process 2 is missing the subnets keyword. This is the most likely cause because, by default, OSPF redistribution without the subnets keyword only redistributes classful network routes, filtering out any classless subnet routes that do not match the major network boundary. When troubleshooting missing routes in a redistribution scenario between OSPF processes, the subnets keyword is essential to ensure all subnetted prefixes are injected as Type 5 external LSAs into the destination OSPF database. On the Cisco CCNP ENARSI 300-410 exam, this is a classic trap: engineers often configure the redistribute command but forget the subnets keyword, leading to incomplete routing tables that appear to have no external routes. A reliable memory tip is to think "subnets for subnets"—if you want to redistribute any subnet, you must include the subnets keyword, or only the classful network will appear.
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting a route redistribution issue between two OSPF processes. Router R1 runs OSPF process 1 and OSPF process 2, and redistributes routes between them. The engineer notices that routes from OSPF process 1 are not appearing in the OSPF database of process 2, even though the redistribute command is configured. The show ip ospf database command on R1 for process 2 shows no external routes. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The redistribute ospf 1 command under OSPF process 2 is missing the subnets keyword.
When redistributing between OSPF processes, the redistribute command must include the subnets keyword to redistribute classless subnets. Without it, only classful networks are redistributed, which may cause many routes to be missing.
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 redistribute ospf 1 command under OSPF process 2 is missing the subnets keyword.
Why this is correct
Correct: Without subnets, only classful networks are redistributed, causing many missing routes.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
OSPF process 1 has a higher administrative distance than OSPF process 2.
Why it's wrong here
Administrative distance is not relevant when redistributing between processes on the same router.
✗
The redistribute ospf 1 command under OSPF process 2 is missing the match internal keyword.
Why it's wrong here
Redistribution between OSPF processes includes all routes by default; match internal is not applicable here.
✗
OSPF process 2 has a route map applied that is filtering all routes.
Why it's wrong here
While possible, the missing subnets keyword is a more common and likely cause.
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
Keyword trap
While possible, the missing subnets keyword is a more common and likely cause.
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.
Route Redistribution — This question tests Route Redistribution — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The redistribute ospf 1 command under OSPF process 2 is missing the subnets keyword. — When redistributing between OSPF processes, the redistribute command must include the subnets keyword to redistribute classless subnets. Without it, only classful networks are redistributed, which may cause many routes to be missing.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer is troubleshooting a route redistribution issue between RIP and OSPF. Router R1 runs both RIP and OSPF, and redistributes RIP routes into OSPF. The engineer notices that RIP routes are not appearing in the OSPF database on neighboring routers. The show ip ospf database external command on a neighbor shows no external routes from R1. The redistribute rip command is configured under OSPF on R1. What is the most likely cause?
medium
✓ A.The redistribute rip command under OSPF is missing the subnets keyword.
B.RIP has a higher administrative distance than OSPF.
C.The OSPF process on R1 has a distribute-list blocking these routes.
D.The RIP process on R1 is not running.
Why A: When redistributing into OSPF, the subnets keyword is required to redistribute classless subnets. Without it, only classful networks are advertised, which may cause many routes to be missing.
Variation 2. A network engineer is troubleshooting a route redistribution issue between OSPF and BGP. Router R1 runs both OSPF and BGP, and redistributes OSPF routes into BGP. The engineer notices that OSPF external routes are not appearing in the BGP table on R1. The show ip bgp command does not list these prefixes. The redistribute ospf 1 match external command is configured under BGP. What is the most likely cause?
hard
✓ A.The redistribute ospf 1 match external command under BGP is missing the subnets keyword.
B.OSPF has a higher administrative distance than BGP.
C.The OSPF process on R1 has a distribute-list blocking these routes.
D.BGP requires the network command to advertise routes, not redistribution.
Why A: When redistributing OSPF into BGP, the subnets keyword is required to redistribute classless subnets. Without it, only classful networks are redistributed, which may cause many routes to be missing.
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Question Discussion
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