- A
EIGRP is using passive interfaces on the core routers, preventing rapid updates.
Why wrong: Incorrect. Passive interfaces prevent EIGRP from forming adjacencies, but if they are passive, no convergence would occur. The scenario implies adjacencies exist.
- B
The failed link was the only feasible successor for the affected routes, causing EIGRP to go into active state and query neighbors.
Correct. When the only feasible successor fails, EIGRP transitions to active state and sends queries to all neighbors. The time to receive all replies can exceed 15 seconds, especially in large networks.
- C
EIGRP hold timers are set to 180 seconds by default, causing slow detection.
Why wrong: Incorrect. Default hold timers are 15 seconds on LAN interfaces, not 180 seconds. The slow convergence is not due to timer defaults.
- D
The engineer configured 'eigrp stub' on the core routers, which prevents query propagation.
Why wrong: Incorrect. Stub routers do not propagate queries, which can speed convergence. This would not cause slow convergence.
Quick Answer
The answer is that the failed link was the only feasible successor for the affected routes, forcing EIGRP into the active state query process. When a route loses its last feasible successor, EIGRP cannot perform a local recomputation using the Diffusing Update Algorithm (DUAL) and must instead transition to the active state, sending query packets to all neighbors. In a fully meshed core, this query/reply process must wait for every neighbor to respond, and with default timers, the cumulative delay easily exceeds 15 seconds—especially if any neighbor is slow to reply. On the ENCOR 350-401 exam, this scenario tests your understanding of DUAL’s finite state machine and the distinction between passive and active states; a common trap is assuming that multiple equal-cost paths automatically prevent convergence delays, but without a feasible successor, the route still goes active. Memory tip: “No FS, no local fix—DUAL goes active, and queries stick.”
CCNP EIGRP Practice Question
This 350-401 practice question tests your understanding of eigrp. 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.
A network engineer is designing an EIGRP network with multiple routers. The network has a core layer where all routers are fully meshed. The engineer wants to ensure that if a link fails, EIGRP converges quickly without relying on route redistribution or static routes. The engineer configures EIGRP with default timers. However, during a failure simulation, convergence takes over 15 seconds. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 failed link was the only feasible successor for the affected routes, causing EIGRP to go into active state and query neighbors.
When the only feasible successor (FS) for a route fails, EIGRP cannot perform a local recomputation and must transition the route to the active state. It then sends query packets to all neighbors to find an alternative path, which introduces significant delay due to the need to wait for replies from every neighbor in a fully meshed core. With default timers, this query/reply process can easily exceed 15 seconds, especially if any neighbor is slow to respond.
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.
- ✗
EIGRP is using passive interfaces on the core routers, preventing rapid updates.
Why it's wrong here
Incorrect. Passive interfaces prevent EIGRP from forming adjacencies, but if they are passive, no convergence would occur. The scenario implies adjacencies exist.
- ✓
The failed link was the only feasible successor for the affected routes, causing EIGRP to go into active state and query neighbors.
Why this is correct
Correct. When the only feasible successor fails, EIGRP transitions to active state and sends queries to all neighbors. The time to receive all replies can exceed 15 seconds, especially in large networks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
EIGRP hold timers are set to 180 seconds by default, causing slow detection.
Why it's wrong here
Incorrect. Default hold timers are 15 seconds on LAN interfaces, not 180 seconds. The slow convergence is not due to timer defaults.
- ✗
The engineer configured 'eigrp stub' on the core routers, which prevents query propagation.
Why it's wrong here
Incorrect. Stub routers do not propagate queries, which can speed convergence. This would not cause slow convergence.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that EIGRP convergence is always fast due to its DUAL algorithm, but the trap here is that without a feasible successor, the active query process can cause significant delays, especially in a fully meshed network.
Trap categories for this question
Scenario analysis trap
Incorrect. Passive interfaces prevent EIGRP from forming adjacencies, but if they are passive, no convergence would occur. The scenario implies adjacencies exist.
Detailed technical explanation
How to think about this question
EIGRP uses the Diffusing Update Algorithm (DUAL) to maintain loop-free paths. A feasible successor is a backup route that meets the feasibility condition (reported distance < feasible distance). When the successor fails and no FS exists, the route goes active, and the router sends queries to all neighbors. In a fully meshed core, each router must reply, and if any reply is delayed (e.g., due to a slow link or router), the convergence time increases dramatically. This is why EIGRP can be slow in large, fully meshed topologies without tuning timers or using techniques like stub routing or summarization.
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 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.
What to study next
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FAQ
Questions learners often ask
What does this 350-401 question test?
EIGRP — This question tests EIGRP — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The failed link was the only feasible successor for the affected routes, causing EIGRP to go into active state and query neighbors. — When the only feasible successor (FS) for a route fails, EIGRP cannot perform a local recomputation and must transition the route to the active state. It then sends query packets to all neighbors to find an alternative path, which introduces significant delay due to the need to wait for replies from every neighbor in a fully meshed core. With default timers, this query/reply process can easily exceed 15 seconds, especially if any neighbor is slow to respond.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 24, 2026
This 350-401 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 350-401 exam.
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