300-410 Layer 3 Technologies Practice Question
A network engineer is configuring route redistribution between EIGRP and OSPF on a Cisco IOS-XE router. The engineer wants to prevent routing loops and ensure that only specific EIGRP routes are redistributed into OSPF. Which combination of tools should the engineer use?
⚠ Common exam trap
The trap here is thinking that a distribute-list alone can prevent loops during mutual redistribution, when route tagging is required to identify and block redistributed routes from re-entering the original protocol.
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
✓
Use a route map with a prefix list to match specific routes, and set a tag on redistributed routes to prevent them from being redistributed back into EIGRP.
To control redistribution and prevent loops, a route map with a prefix list filters which EIGRP routes enter OSPF, while route tagging marks those routes so EIGRP can deny them if they are redistributed back. This combination is the most precise and scalable method. The other options either do not filter properly, break connectivity, or rely on mechanisms that do not prevent loops during mutual redistribution.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use a route map with a prefix list to match specific routes, and set a tag on redistributed routes to prevent them from being redistributed back into EIGRP.
Why this is correct
A route map with a prefix list provides granular control over which EIGRP routes are redistributed into OSPF. Setting a tag on those routes allows EIGRP to deny routes with that tag when redistributing back, preventing loops. This is a standard best practice for mutual redistribution, ensuring only intended routes are advertised and loop prevention is enforced.
- ✗
Configure OSPF as a stub area to prevent external routes from being injected, and redistribute only connected routes into EIGRP.
Why it's wrong here
Configuring OSPF as a stub area prevents external LSAs from entering the area, but it does not control redistribution from EIGRP into OSPF. In fact, a stub area cannot import external routes, so redistributed EIGRP routes would be blocked. This does not meet the requirement to redistribute specific EIGRP routes into OSPF and would break connectivity.
- ✗
Use a distribute-list on the OSPF process to filter routes, and rely on OSPF's built-in loop prevention mechanisms.
Why it's wrong here
A distribute-list can filter routes, but it is applied to routing updates and does not automatically prevent loops during mutual redistribution. OSPF does not have inherent loop prevention for redistributed routes; it relies on external route tags or administrative distance. Without tagging, routes could be redistributed back and cause suboptimal routing or loops.
- ✗
Set the administrative distance of EIGRP to a lower value than OSPF, and use passive interfaces to control updates.
Why it's wrong here
Administrative distance affects route selection when the same prefix is learned from multiple sources, but it does not filter which routes are redistributed. Passive interfaces prevent routing updates on an interface but do not control redistribution. This approach does not provide the granular filtering or loop prevention needed for mutual redistribution.
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
ACL-Based Traffic Filtering and Policy-Based Routing
Key term
Policy Based Routing
Policy Based Routing (PBR) is a technology that allows network traffic to be forwarded based on user-defined policies rather than just the destination IP address in the routing table.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.