- A
Split horizon
Correct. Split horizon prohibits a router from sending an update about a route out the same interface it was learned on, thus preventing the router from learning a route it originally advertised.
- B
Route poisoning
Why wrong: Incorrect. Route poisoning is used to mark a route as unreachable (infinite metric) and advertise it to neighbors, but it does not prevent a router from accepting a self-originated route.
- C
Feasibility condition
Why wrong: Incorrect. The feasibility condition ensures loop-free path selection by comparing reported distance to feasible distance, but it does not directly prevent acceptance of a route that originated from the router itself.
- D
Hold-down timer
Why wrong: Incorrect. Hold-down timers are used in distance-vector protocols to prevent flapping routes from being prematurely accepted, but they do not specifically prevent self-originated route acceptance.
EIGRP Feasibility Condition
This 300-410 practice question tests your understanding of eigrp troubleshooting. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: split Horizon. 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.
Which EIGRP loop prevention mechanism prevents a router from installing a route that was originally learned from itself?
Quick Answer
The answer is the feasibility condition. This EIGRP loop prevention mechanism is correct because it enforces the rule that a router will only accept a route from a neighbor if that neighbor’s reported distance (RD) is strictly less than the router’s own feasible distance (FD) to that destination. By ensuring the neighbor’s path is closer to the destination than the current best path, the feasibility condition guarantees that the route cannot have been learned from the router itself, thus preventing a routing loop. On the Cisco CCNP ENARSI 300-410 exam, this concept often appears in questions about Diffusing Update Algorithm (DUAL) operation, where a common trap is confusing the feasibility condition with the successor or feasible successor selection. Remember that the feasibility condition is a strict inequality—RD must be less than FD, not less than or equal. A simple memory tip: “Reported Distance must be Less than Feasible Distance” or “RD < FD for a Feasible Successor.”
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
Split horizon
Split horizon prevents a router from advertising a route back out the interface from which it was learned, thereby preventing the router from receiving and installing a route that originated from itself. This is the primary loop prevention mechanism that stops self-originated routes from being accepted. The feasibility condition in EIGRP ensures loop-free paths by requiring that the reported distance from a neighbor be less than the feasible distance, but it does not specifically prevent self-originated route acceptance.
Key principle: Split Horizon
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Split horizon
Why this is correct
Correct. Split horizon prohibits a router from sending an update about a route out the same interface it was learned on, thus preventing the router from learning a route it originally advertised.
Related concept
Split Horizon
- ✗
Route poisoning
Why it's wrong here
Incorrect. Route poisoning is used to mark a route as unreachable (infinite metric) and advertise it to neighbors, but it does not prevent a router from accepting a self-originated route.
- ✗
Feasibility condition
Why it's wrong here
Incorrect. The feasibility condition ensures loop-free path selection by comparing reported distance to feasible distance, but it does not directly prevent acceptance of a route that originated from the router itself.
- ✗
Hold-down timer
Why it's wrong here
Incorrect. Hold-down timers are used in distance-vector protocols to prevent flapping routes from being prematurely accepted, but they do not specifically prevent self-originated route acceptance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often confuse the feasibility condition with split horizon. While both prevent loops, split horizon specifically stops a router from installing a route it originated.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Split Horizon
- Feasibility Condition
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Split Horizon
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.
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.
What to study next
Got this wrong? Here's your next step.
Review split Horizon, then practise related 300-410 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 300-410 question test?
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Split Horizon.
What is the correct answer to this question?
The correct answer is: Split horizon — Split horizon prevents a router from advertising a route back out the interface from which it was learned, thereby preventing the router from receiving and installing a route that originated from itself. This is the primary loop prevention mechanism that stops self-originated routes from being accepted. The feasibility condition in EIGRP ensures loop-free paths by requiring that the reported distance from a neighbor be less than the feasible distance, but it does not specifically prevent self-originated route acceptance.
What should I do if I get this 300-410 question wrong?
Review split Horizon, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Split Horizon
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Last reviewed: Jun 18, 2026
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