The answer is an excessively low OSPF hello interval combined with the default dead interval, which causes neighbor flapping when the router is under high CPU load from redistribution. When OSPF redistributes EIGRP routes on a broadcast multi-access link, the router must generate and flood many LSAs, consuming CPU cycles. If the hello interval is set to 10 seconds but the dead interval remains at the default 40 seconds, a brief spike in CPU utilization can cause the router to miss sending or receiving hello packets within the dead timer, triggering a neighbor reset. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF timer interaction with route redistribution overhead—a common trap is to blame the redistribution process itself rather than the timer mismatch. Remember that on broadcast networks, the default dead interval is four times the hello interval; if you lower the hello interval without adjusting the dead interval proportionally, you shrink the tolerance for CPU delays. Memory tip: “Four times the hello, or your neighbor will go.”
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 configures redistribution between OSPF and EIGRP on a multi-access link. After configuration, OSPF neighbors keep flapping. Router R1 config:
interface GigabitEthernet0/0
ip ospf network broadcast
ip ospf hello-interval 10
!
router ospf 1
redistribute eigrp 100 subnets
!
router eigrp 100
redistribute ospf 1 metric 10000 100 255 1 1500
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.1.2 1 FULL/DR 00:00:35 10.1.1.2 GigabitEthernet0/0
192.168.1.3 1 2WAY/DROTHER 00:00:31 10.1.1.3 GigabitEthernet0/0
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The OSPF hello interval is too low, causing neighbor flapping under load from redistribution.
The OSPF network type is broadcast, but the EIGRP redistribution may be causing OSPF LSAs to be flooded with high CPU load, leading to neighbor flapping. Additionally, the hello interval is set to 10 seconds, but the dead interval is not explicitly set, defaulting to 40 seconds. If the router is overloaded, hello packets may be missed. The fix is to increase the dead interval or adjust the network type to point-to-point.
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 OSPF hello interval is too low, causing neighbor flapping under load from redistribution.
Why this is correct
Redistribution increases CPU load, causing hello packets to be delayed and neighbors to time out.
The OSPF network type broadcast requires a DR/BDR election, causing instability.
Why it's wrong here
DR/BDR election is stable; the issue is hello timing.
✗
The redistribute command under OSPF is missing the metric type.
Why it's wrong here
Missing metric type does not cause neighbor flapping.
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.
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 OSPF hello interval is too low, causing neighbor flapping under load from redistribution. — The OSPF network type is broadcast, but the EIGRP redistribution may be causing OSPF LSAs to be flooded with high CPU load, leading to neighbor flapping. Additionally, the hello interval is set to 10 seconds, but the dead interval is not explicitly set, defaulting to 40 seconds. If the router is overloaded, hello packets may be missed. The fix is to increase the dead interval or adjust the network type to point-to-point.
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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