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300-410 Practice Question: An engineer configures EIGRP named mode on a…
An engineer configures EIGRP named mode on a router. After a link failure, a route becomes stuck-in-active (SIA). The engineer checks the EIGRP topology and notices that the route has a feasible successor. Which is the most likely explanation?
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 router received a query from a neighbor and must reply, but the reply is delayed because the feasible successor's route is also being queried.
In EIGRP, if a route has a feasible successor, the router will immediately use it without going active. However, if the feasible successor's route is also invalidated (e.g., due to a metric change) or if the query process is triggered by a neighbor that does not have a feasible successor, the router may still go active. A common corner case is when the feasible successor is not used because the route is in a 'stuck-in-active' state due to a query from a neighbor that did not receive a reply, even though the local router has a feasible successor. This can happen if the router receives a query from a neighbor and must reply, but the reply is delayed.
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 router received a query from a neighbor and must reply, but the reply is delayed because the feasible successor's route is also being queried.
Why this is correct
Even with a feasible successor, the router must reply to queries from neighbors. If the reply is delayed (e.g., due to a unidirectional link), the local router may become SIA.
- ✗
The feasible successor is not used because the route is in passive mode, and the router must wait for the active timer to expire.
Why it's wrong here
If a feasible successor exists, the route should remain passive. The active timer is only relevant when going active.
- ✗
The named mode EIGRP does not support feasible successors, so the router must always go active.
Why it's wrong here
Named mode EIGRP fully supports feasible successors, just like classic mode.
- ✗
The feasible successor's metric is higher than the successor's, so it is not considered as a backup.
Why it's wrong here
A feasible successor must meet the feasibility condition (AD < FD). If it does, it is used. Metric comparison is not the issue.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.