The correct answer is that mutual redistribution without route filtering can cause routing loops or suboptimal routing. This occurs because when two routing protocols—here, EIGRP and OSPF—redistribute routes into each other without any filtering mechanism, a route learned from one protocol can be re-injected back into its source protocol, creating a feedback loop that destabilizes the routing table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of redistribution pitfalls, often appearing as a configuration-based multiple-choice question where the trap is assuming that simply enabling redistribution is sufficient. The key technical concept is that without route-maps, distribute-lists, or administrative distance adjustments, routers have no way to distinguish between internal and redistributed routes, leading to potential loops. A practical memory tip is "filter or flop"—always apply a filter when redistributing bidirectionally to prevent the routing table from flipping between paths.
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.
Consider the following configuration on Router R4:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Mutual redistribution without route filtering can cause routing loops or suboptimal routing.
Mutual redistribution without route filtering or administrative distance adjustments can cause routing loops or suboptimal routing. The configuration does not include any route-maps or distribute-lists to control which routes are redistributed, which is a common pitfall.
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 configuration is correct and will work without issues.
Why it's wrong here
Mutual redistribution without filtering can lead to loops.
✗
The 'metric-type 1' in OSPF redistribution may cause EIGRP routes to be preferred over OSPF routes.
Why it's wrong here
The metric type does not directly cause preference issues; it's the lack of filtering that is problematic.
✓
Mutual redistribution without route filtering can cause routing loops or suboptimal routing.
Why this is correct
Without filtering, routes can be redistributed back and forth, causing loops.
The EIGRP metric values are invalid because load must be between 1 and 255.
Why it's wrong here
The load value of 1 is valid (range 1-255).
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: Mutual redistribution without route filtering can cause routing loops or suboptimal routing. — Mutual redistribution without route filtering or administrative distance adjustments can cause routing loops or suboptimal routing. The configuration does not include any route-maps or distribute-lists to control which routes are redistributed, which is a common pitfall.
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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