Question 623 of 1,958
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350-401 Practice Question: Is designing an EIGRP network with multiple…
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
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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Last reviewed: Jun 24, 2026
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