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300-410 Practice Question: An engineer is troubleshooting a route…
An engineer is troubleshooting a route redistribution issue between EIGRP and OSPF. Which TWO actions will prevent routing loops in a mutual redistribution scenario? (Choose TWO.)
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
✓
Configure a higher administrative distance for routes learned via redistribution (e.g., distance 200 for OSPF external routes) to prefer the original protocol's routes.
To prevent routing loops during mutual redistribution, you must ensure that routes redistributed from one protocol are not re-injected back into the source protocol. Common methods include setting administrative distance values (e.g., using 'distance' command) or using route tagging with distribute lists or route maps to filter. Simply increasing the metric for redistributed routes does not prevent loops, and disabling auto-summary is unrelated to loop prevention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure a higher administrative distance for routes learned via redistribution (e.g., distance 200 for OSPF external routes) to prefer the original protocol's routes.
Why this is correct
Correct. By increasing the administrative distance for redistributed routes, you ensure that the original protocol's routes (with lower AD) are preferred, reducing the chance of a loop where a redistributed route is preferred over the original.
- ✗
Use the 'default-metric' command to set a consistent seed metric for redistributed routes, ensuring all routes have the same metric.
Why it's wrong here
Incorrect. Setting a consistent metric helps with route selection but does not prevent loops. Loops occur when routes are re-redistributed, not due to metric inconsistency.
- ✓
Apply route tags to redistributed routes and use distribute lists or route maps to prevent re-redistribution of tagged routes back into the original protocol.
Why this is correct
Correct. Tagging routes allows you to identify routes that were originally from one protocol and filter them when redistributing back, preventing loops.
- ✗
Enable 'auto-summary' on both routing protocols to summarize routes at classful boundaries, reducing the number of routes and loop potential.
Why it's wrong here
Incorrect. Auto-summary can actually cause suboptimal routing and does not prevent loops. It is not a loop prevention mechanism.
- ✗
Configure 'passive-interface' on all interfaces where redistribution is performed to prevent routing updates from being sent.
Why it's wrong here
Incorrect. Passive-interface prevents routing updates from being sent out an interface, but it does not prevent redistribution loops. It is used for other purposes like suppressing unnecessary updates.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
OSPF Neighbor Adjacency and Basics
Key term
Route Redistribution Between Protocols
Route redistribution between protocols is the process of taking routes learned from one routing protocol and injecting them into another routing protocol so that networks using different protocols can communicate.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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