The answer is that the redistribute eigrp command under OSPF is missing the subnets keyword. When redistributing routes into OSPF, the subnets keyword is required to advertise classless subnets; without it, OSPF only redistributes classful network routes, and for any route that is not directly connected to the redistributing router, the next-hop is set to 0.0.0.0, meaning the router considers itself the next hop, which breaks proper forwarding. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF redistribution behavior and the critical role of the subnets keyword—a common trap is assuming the route is missing from the routing table entirely. A reliable memory tip is: "No subnets, no subnet mask; next-hop zero, traffic won't pass."
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 EIGRP and OSPF. Routers R1 (EIGRP) and R2 (OSPF) are redistributing routes. The engineer notices that some EIGRP routes are appearing in the OSPF database on R2, but traffic to those destinations is not being forwarded correctly. The show ip route command on R2 shows the redistributed routes with a next-hop of 0.0.0.0. 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 eigrp command under OSPF is missing the subnets keyword.
When redistributing into OSPF, if the redistributed routes are not directly connected to the redistributing router, the next-hop may be set to 0.0.0.0 (self) if the subnets keyword is missing or if the route is not in the routing table. However, a common cause is that the redistribute command is missing the subnets keyword, causing classful behavior.
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 eigrp command under OSPF is missing the subnets keyword.
Why this is correct
Correct: Without subnets, the next-hop may be set to 0.0.0.0 for classless routes.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The EIGRP routes are not in the routing table on R2.
Why it's wrong here
If they were not in the routing table, they would not be redistributed.
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 eigrp command under OSPF is missing the subnets keyword. — When redistributing into OSPF, if the redistributed routes are not directly connected to the redistributing router, the next-hop may be set to 0.0.0.0 (self) if the subnets keyword is missing or if the route is not in the routing table. However, a common cause is that the redistribute command is missing the subnets keyword, causing classful behavior.
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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