- A
The reported distance must be less than the feasible distance.
This is the feasibility condition defined by EIGRP.
- B
The metric must be equal to the successor's metric.
Why wrong: Equal metrics are not required; the condition is based on reported distance.
- C
The next-hop router must be directly connected.
Why wrong: The next hop must be reachable, but not necessarily directly connected.
- D
The route must be learned from the same AS.
Why wrong: Routes from different ASes are not considered in EIGRP.
Question 2,029 of 2,152
The Feasible Successor Condition in EIGRP: Reported Distance vs Feasible Distance
This 300-410 practice question tests your understanding of eigrp troubleshooting. 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.
Which of the following is a mandatory condition for a route to be considered a feasible successor in EIGRP?
Quick Answer
The answer is that the reported distance must be less than the feasible distance. This mandatory condition ensures the alternate path is loop-free because the neighbor’s reported distance represents its own cost to the destination, and if that value is lower than the current successor’s feasible distance, the neighbor cannot be using a path that goes back through the local router. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of EIGRP’s Diffusing Update Algorithm (DUAL) and its loop-avoidance mechanism; a common trap is confusing reported distance with feasible distance or thinking the feasible distance itself must change. To remember the feasible successor condition, keep this mnemonic: “RD must be less than FD to keep the path loop-free.”
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
✓
The reported distance must be less than the feasible distance.
In EIGRP, a feasible successor is a backup route that can be used immediately if the successor fails. The mandatory condition for a route to be considered a feasible successor is that its reported distance (RD) must be less than the feasible distance (FD) of the current successor. This ensures the backup route is loop-free, as per the Diffusing Update Algorithm (DUAL).
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 reported distance must be less than the feasible distance.
Why this is correct
This is the feasibility condition defined by EIGRP.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The metric must be equal to the successor's metric.
Why it's wrong here
Equal metrics are not required; the condition is based on reported distance.
- ✗
The next-hop router must be directly connected.
Why it's wrong here
The next hop must be reachable, but not necessarily directly connected.
- ✗
The route must be learned from the same AS.
Why it's wrong here
Routes from different ASes are not considered in EIGRP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a feasible successor must have a metric equal to or better than the successor, but the actual condition is that the reported distance must be strictly less than the feasible distance.
Detailed technical explanation
How to think about this question
The feasible distance (FD) is the best metric to a destination, and the reported distance (RD) is the metric advertised by a neighbor. DUAL uses the RD < FD condition to guarantee loop-free paths without requiring periodic updates. In real-world scenarios, if the successor fails, EIGRP can instantly switch to a feasible successor without recalculating, which is critical for fast convergence in large networks.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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
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FAQ
Questions learners often ask
What does this 300-410 question test?
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The reported distance must be less than the feasible distance. — In EIGRP, a feasible successor is a backup route that can be used immediately if the successor fails. The mandatory condition for a route to be considered a feasible successor is that its reported distance (RD) must be less than the feasible distance (FD) of the current successor. This ensures the backup route is loop-free, as per the Diffusing Update Algorithm (DUAL).
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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